Manual of Neuro-ophthalmology
Manual of Neuro-ophthalmology
Amar Agarwal MS FRCS FRCOphth Athiya Agarwal MD DO Dr Agarwal’s Group of Eye Hospitals and Eye Research Centre 19, Cathedral Road, Chennai - 600 086, India
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[email protected] Manual of Neuro-ophthalmology © 2008, Jaypee Brothers Medical Publishers All rights reserved. No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the authors and the publisher. This book has been published in good faith that the material provided by authors is original. Every effort is made to ensure accuracy of material, but the publisher, printer and authors will not be held responsible for any inadvertent error(s). In case of any dispute, all legal matters are to be settled under Delhi jurisdiction only.
First Edition: 2009 ISBN 978-81-8448-411-3 Typeset at JPBMP typesetting unit Printed at Ajanta
This book is dedicated to a lovely couple
Marguerite Mcdonald and Stephen Klyce
Contributors Amar Agarwal MS FRCS FRCOPHTH Dr. Agarwal’s Group of Eye Hospitals and Eye Research Centre 19, Cathedral Road Chennai-600 086, India
[email protected] Athiya Agarwal MD DO Dr. Agarwal’s Group of Eye Hospitals and Eye Research Centre 19, Cathedral Road Chennai-600 086, India
[email protected] Garrett Smith MD Moran Eye Center Salt Nake City, UTAH USA Jeyalakshmi Govindan DO DNB Consultant Ophthalmologist Dr. Agarwal’s Eye Hospital 19, Cathedral Road Chennai, India Nick Mamalis MD Moran Eye Center Salt Nake City, UTAH USA P Ramesh MBBS DMRD DNB MNAMS FRCR Director, Liberty Scans Chennai, India Priya Narang MS Narang Eye Hospital Ahmedabad, Gujarat, India
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Manual of Neuro-ophthalmology
Reena M Choudhry MD DO DNB FRCS Icare Eye Hospital and Postgraduate Institute Noida, Uttar Pradesh India Sameer Narang MS Narang Eye Hospital Ahmedabad, Gujarat India Saurabh Choudhry MD DO DNB Icare Eye Hospital and Postgraduate Institute Noida, Uttar Pradesh India S Soundari DO DNB FRCS Consultant Ophthalmologist Dr. Agarwal’s Eye Hospital 19, Cathedral Road Chennai India
Foreword Neuro-ophthalmology is a complex subspecialty which requires keen skills of clinical observation, attention to detail, and intricate thought processes in order to formulate the appropriate diagnostic and therapeutic plan for the patient. What makes the field even more challenging is our limited knowledge of the intricate neurological pathways between the eye and the brain; many of which are still being discovered, as long as our understanding is evolving. To concisely and accurately explain the basics of neuroophthalmology is a difficult task, as it requires a thorough understanding of the subject as well as a natural gift for simplifying and organizing the material so that it appeals to a wide audience. Through the process of teamwork, the Agarwals’ have succeeded in creating an outstanding book for neuro-ophthalmology that will prove to be an excellent reference for a full spectrum of readers, from medical students to practising ophthalmologists. Prof Amar Agarwal once explained to me that for any challenging situation, “The battle is in the brain”. Whether the task is climbing Mount Everest or writing a complete library of ophthalmology texts, the true challenge is in mind. Having the drive and determination to succeed, no matter the situation, is the mark of a true pioneer, and a characteristic of one of my strongest mentors, Prof Amar Agarwal. Uday Devgan MD FACS Chief of Ophthalmology Olive View-UCLA Medical Center UCLA School of Medicine Private Ophthalmic Practice Maloney Vision Institute Los Angeles, California, USA
Preface Understanding Neuro-ophthalmology is a challenge. It took us a long time to comprehend the basics in this field when we were residents. That is the notion why we have written Manual of Neuro-ophthalmology. The idea is that you dear reader can go through the text and figures and never have difficulty in understanding this subject like we did. We would like to thank our consultant Dr S Soundari for helping us. Shri JP Vij and his full team of M/s Jaypee Brothers Medical Publishers have always supported our writing endeavors. Our sincere thanks to them. Finally, dear reader we hope this book will change your outlook to Neuro-ophthalmology. Amar Agarwal Athiya Agarwal
Contents 1. Supranuclear Pathways for Eye Movements ..................................... 1 Athiya Agarwal, Amar Agarwal 2. Supranuclear Disorders of Eye Movements ....................................17 Athiya Agarwal, Amar Agarwal 3. Nystagmus .............................................................................................32 Athiya Agarwal, Amar Agarwal 4. The Pupil ................................................................................................54 Athiya Agarwal, Amar Agarwal 5. Visual Pathway .....................................................................................73 Athiya Agarwal 6. Anatomy of the Optic Nerve ............................................................ 103 Athiya Agarwal 7. Oculomotor Nerve ............................................................................. 109 Athiya Agarwal 8. Lesions of the Oculomotor Nerve ................................................... 118 Athiya Agarwal 9. Trochlear Nerve and its Lesions ..................................................... 123 Athiya Agarwal 10. Abducent Nerve and its Lesions ..................................................... 132 Athiya Agarwal 11. Trigeminal Nerve .............................................................................. 140 Athiya Agarwal 12. Facial Nerve and its Lesions ............................................................ 145 Athiya Agarwal 13. Congenital Optic Nerve Anomalies ................................................ 150 Priya Narang, Sameer Narang, Amar Agarwal 14. Optic Nerve Tumors ......................................................................... 157 Nick Mamalis, Garrett Smith 15. Abnormalities of Optic Nerve Head .............................................. 185 Reena M Choudhry, Saurabh Choudhry, Amar Agarwal 16. Ocular Myopathies ............................................................................ 197 S Soundari 17. Miscellaneous .................................................................................... 204 Jeyalakshmi Govindan, S Soundari 18. Examination of a Neuro-ophthalmology Case .............................. 219 S Soundari 19. Imaging in Neuro-ophthalmology .................................................. 226 P Ramesh Index ..................................................................................................... 253
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Supranuclear Pathways for Eye Movements Athiya Agarwal, Amar Agarwal
INTRODUCTION One is always confused about supranuclear pathways. We understand the pathways of the III, IV and VI cranial nerve nuclei. We would be able to trace it from the brain to the superior orbital fissure, but we fail to remember that these pathways we are discussing are the infranuclear pathways which extend from the cranial nerve nuclei to the ocular muscle. We need to also understand the anatomy of the supranuclear pathways.1,2 SUPRANUCLEAR AND INFRANUCLEAR PATHWAYS Anatomical pathways, which extend from the cortical centers of the brain to the cranial nerve nuclei, are called the supranuclear pathways. From the cranial nerve nuclei to the ocular muscle exist the infranuclear pathways (Fig. 1.1). In peripheral nerves, the nerve starts from the brain and reaches the anterior horn cell in the spinal cord. This is the upper motor neuron. From the anterior horn cell of the spinal cord, the nerve moves to the peripheral muscle. This is the lower motor neuron. If there is a lower motor neuron disease the limb is flaccid and if there is an upper motor neuron disease the limb is spastic. The cranial nerve nuclei are like peripheral nerve nuclei. From the cortex of the brain the nerve extends to the cranial nerve nuclei and this is the upper motor neuron (UMN) pathway. From the cranial nerve nuclei the nerve extends to the ocular muscle and this is the lower motor neuron (LMN) pathway. In peripheral nerves if the anterior horn cell gets involved as in poliomyelitis, the patient has a LMN disease and so the limb is flaccid. The anterior horn cell is akin to the cranial nerve nuclei of cranial nerves. So, if the cranial nerve nuclei gets involved the lesion produced will be a LMN lesion.
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Fig. 1.1: Supranuclear pathway
SUPRANUCLEAR EYE MOVEMENT SYSTEMS There are five supranuclear eye movement systems. They are: 1. Saccadic system 2. Pursuit system 3. Vergence system 4. Non-optic reflex system 5. Position maintenance system. SACCADIC SYSTEM The saccadic system is otherwise known as the fast eye movement system or rapid eye movement system. This is because the saccadic system controls the fast eye movements. These are command movements. For example if we say, look to the right, the eyes turn to the right. This occurs rapidly and is a rapid eye movement. The system, which controls this command pathway, is the saccadic system. The saccadic system originates from the frontal lobe of the brain. The impulses then move to the mesencephalic system and so the anatomical pathway subserving the fast eye movements is the
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frontomesencephalic pathway. When you watch someone watching a game of tennis or table tennis, you will notice the eyes move rapidly from one end of the court or table to the other. The eyes keep on darting from one end to the other. These are fast eye movements controlled by the frontomesencephalic pathway. Horizontal Saccades The saccades can in turn be horizontal or vertical. In horizontal saccades, the eyes move horizontally and in vertical saccades, the eyes move up and down. Let us now understand the pathway of the horizontal saccades (Fig. 1.2).
Fig. 1.2: Horizontal saccade pathway LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.LobeOccipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
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If the eyes have to look to the right, then the command for this movement is given by the left frontal lobe in area 8 of the cortex. The nerves cross over to the opposite side and reach the right pontine gaze center. From here the nerves pass to the same side (in this case the right) VI nerve nuclei. From the right pontine gaze center nerves also pass to the opposite III nerve nuclei. In this case this will be the left III nerve nuclei. All the cranial nerve nuclei are connected with each other through the medial longitudinal fasciculus or medial longitudinal bundle. In other words from the right pontine gaze center, the nerves pass through the medial longitudinal bundle to the left III cranial nerve nuclei. Till here is the supranuclear pathway. This is why this is also called the frontomesencephalic pathway. From the right VI nerve nucleus nerves then pass to the lateral rectus muscle of the right eye. From the left III nerve nucleus nerves pass to the left medial rectus muscle. These are the infranuclear pathways and both the eyes move to the right. At this stage it is important to understand a bit more on the medial longitudinal bundle. As just explained, the nerves pass from the pontine gaze center to the VI and III nerve nuclei through the medial longitudinal bundle. If there is a lesion in the medial longitudinal bundle, these fibers are cut and there would not be a correlation between the III nerve and the VI nerve. This leads to the condition called internuclear ophthalmoplegia. Vertical Saccades The pathway for the vertical saccades is still doubtful. Vertical saccades depend on simultaneous bilateral activity within the frontal lobes in Area 8 (Fig. 1.3). This means that the horizontal saccades are unilaterally controlled whereas the vertical saccades are bilaterally controlled. If one has to look up or down, impulses travel from both the frontal lobes in Area 8. The impulse travels via the basal ganglia to the pretectal area or the pretectal center for vertical gaze. This is the vertical gaze center. From the vertical gaze center impulses pass to the III nerve nuclei. Till here is the supranuclear pathway. Now, the infranuclear pathway starts and impulses go via the III cranial nerve to the vertical muscles and the patient looks up or looks down. Because of the fact that vertical saccades require bilateral cortical activity, cerebral hemisphere lesions rarely produce deficits in the vertical saccades. Such deficits are seen only with massive hemispheric lesions producing bilateral damage to both frontomesencephalic
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Fig. 1.3: Vertical saccade pathway LE- Left eye; RE- Right eye; Occ.Lobe- Occipital Lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
pathways. Disturbances of vertical saccades are much more common with midbrain disorders. Characteristic of the Saccade The characteristic of the saccades is shown in Table 1.1 compared to the other supranuclear eye movements. From the onset of the stimulus, which is voluntary to the beginning of the recorded saccade, the latent period is about 200 to 250 msec. The velocity of the fast eye movement is 30 to 700 degrees/second.
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PURSUIT SYSTEM The smooth pursuit system is utilized when the eyes follow targets that move smoothly and relatively slowly. It maintains a fixed relationship between the movements of the eyes and the target. As smooth pursuit movements directly relate eye position to target position, they are also termed as following or tracking movements. As these movements are slow, they are called slow eye movements. Imagine a person walking and you are watching that person. When your eyes follow the movement of the person, they will be using the pursuit system. The pathway for the pursuit system starts from the occipital lobe and hence is known as the occipitomesencephalic pathway. There are different pathways for horizontal pursuits and for vertical pursuits. Horizontal Pursuit System Pathway If a target is moving to the right (Fig. 1.4), the first step is that the eyes have to visualize the object. So the pathway starts from the retina
Fig. 1.4: Horizontal pursuit pathway (slow phase) LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.LobeOccipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
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of both eyes. The impulses pass through the optic nerve, optic chiasma, and optic tract and reach the right occipital lobe in area 19. This area subserves the pursuit movements. It is important to note that the occipital areas mediate horizontal pursuit movements to the ipsilateral side. In other words, the right occipital lobe mediates horizontal pursuit movements to the right. From the occipital lobe, impulses go to the same side pontine gaze center. In this case, impulses from the right occipital lobe go to the right Pontine gaze center. From here impulses go to the right VI nerve nucleus and the left III nerve nucleus. Till here is the supranuclear pathway. From the right VI nerve nucleus and the left III nerve nucleus impulses go via the infranuclear pathway to the lateral rectus and the medial rectus. The characteristics of the pursuits are shown in Table 1.1. Corrective Saccade When the target is moving away from the field of vision the eyes which were moving slowly to that side have to come back to their original position. A fast eye movement does this, in other words a saccade. This is the corrective saccade. If a stream of cars are going in front of our vision, then we keep on following one car and when it goes out of the field of vision our eyes would come and fixate back to the car in the center of our field of vision. This would be done by the corrective saccade. As the impulses from the target moving to the right reaches the occipital lobe (Area 19) and the object is going out of the field of Table 1.1: Characteristics of eye movements
Type
Stimulus (msec)
Latency Velocity (Deg./Sec)
Amplitude Conjugacy (Degrees)
1. Saccade 2. Pursuit 3. Vergence
Volition, reflex Target motion Accommodative, fusional Head movement
200 125 160
30-700 < 50 < 20
0.5-9.0 0-90 Age
<100
< 400
0-90
Conjugate Conjugate Disjugate dependent Conjugate
Positions error
125
< 150
<4
Conjugate
Fixation
-
3-12
1-25
Conjugate
Fixation
-
0-30 min/sec
<1
Disjugate
4. Vestibuloocular 5. Corrective saccade 6. Microsaccade 7. Microdrift
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vision the occipital lobe sends impulses to the ipsilateral frontal lobe to perform the corrective saccade. In this case the right occipital lobe (Fig. 1.5) sends impulses to the right frontal lobe (Area 8). This means there has to be a communication between the occipital lobe and the frontal lobe. From the right occipital lobe impulses pass to the frontal lobe via the parietal lobe. From the right frontal lobe, impulses then pass to the left pontine gaze center which in turn sends impulses to the left VI nerve nucleus and the right III nerve nucleus. This is the supranuclear pathway. Then, the infranuclear pathway takes over and impulses go to the respective lateral and medial recti and the eyes move to the left as a fast eye movement. This is the corrective saccade.
Fig. 1.5: Corrective saccade (Horizontal pursuit pathway for the fast phase) LR- lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.LobeOccipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
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One can illustrate this with an optokinetic drum, which is a drum with black and white stripes. The drum is rotated and the eyes fixate on it. When the stripes go away from the field of vision, the corrective saccade occurs. This leads to a type of nystagmus known as optokinetic nystagmus. Parietal Lobe Lesion If the person has a parietal lobe lesion, then there is a problem (Fig. 1.6). When the corrective saccade has to work the impulse would not pass beyond the parietal lobe. Thus, this would lead to a deficit in the corrective saccade. So a deep parietal lobe lesion causes loss or decrease of the fast phase of the optokinetic nystagmus, when movement of the drum is towards the side of the lesion.
Fig. 1.6: Parietal lobe lesion LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.LobeOccipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway
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Vertical Pursuit System Vertical pursuit movements are generated by simultaneous bilateral stimulation of area 19 of the occipital lobe (Fig. 1.7). The axons of the occipital lobe descend to the pretectal area. From the pretectal area impulses travel to the III nerve nuclei. Till here is the supranuclear or UMN pathway. Then from the III nerve nuclei, impulses pass to the vertical muscles via the infranuclear pathway. The pretectal area or pretectal center is the center for vertical gaze, analogous to the pontine gaze center, which is the center for horizontal gazes.
Fig. 1.7: Vertical pursuit pathway LE- Left eye; RE- Right eye; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
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VERGENCE SYSTEM The role of the vergence system is to keep the image of a target on appropriate points (corresponding elements) of the two retinas by controlling the visual axes of the eyes. Thus, vergence is utilized whenever a target falls on noncorresponding retinal elements. For example, if a target is moved towards the eyes, they must turn toward each other (converge) to keep the target on the fovea of each eye. Conversely, as the target is moved further away, the eyes must turn out (diverge) (Actually, divergence does not occur in our eyes.) Vergence is thus a disconjugate (nonparallel) movement of the eyes, in contrast to most other eye movements which are conjugate (parallel). There are two types of vergence. They can be voluntary—when we command our eyes to converge or reflex—when we bring an object or tape towards our nose and the eyes converge while fixating on the object. The characteristics of the vergence movements are shown in Table 1.1. Voluntary Vergence The center for voluntary vergence is situated in area 8 of the frontal lobe (Fig. 1.8). If one wants to converge then a command movement is sent from area 8. These are bilateral impulses and they go to the pretectal area via the basal ganglia. Here there is the convergence area. From the convergence area, impulses go bilaterally to the III and VI nerve nuclei. Till here is the supranuclear pathway. From the III nerve nuclei impulses go to the medial recti to converge. From the VI nerve nuclei inhibitory impulses go to the lateral recti so that the eyes can converge. Thus both the eyes converge. Pursuit or Reflex Vergence In this, the impulses originate from the retina of the two eyes (Fig. 1.9). If a pen is held in front of our eyes and moved towards the nose and if we keep looking at the pen, then the impulses from the two eyes will make the eyes converge by the pursuit vergence pathway. From the retina impulses will go via the optic nerve and tract to area 19 of the occipital lobe. This is a bilateral impulse. From here it goes to the pretectal area where it reaches the convergence area. From here impulses pass bilaterally to the III and VI nerve nuclei. This is the supranuclear pathway. Then positive impulses go to the medial recti and inhibitory impulses to the lateral recti and the eyes converge while looking at the object.
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Fig. 1.8: Voluntary vergence pathway LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.LobeOccipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
NON-OPTIC REFLEX SYSTEM The non-optic reflex system integrates eye movements and the body movements. There are basically three systems in this: (i) semicircular canals, (ii) neck receptors, and (iii) the cerebellum. The characteristics are shown in Table 1.1.
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Fig. 1.9: Pursuit or reflex vergence pathway LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLFMedial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
Semicircular Canals If a lateral semicircular canal is stimulated, the non-optic reflex system starts to work. If the head is rotated to the left (Fig. 1.10), the lateral semicircular canal is stimulated. If we tilt our head to the left, the eyes should generally keep looking straight ahead (the ultimate aim of the whole process). For the eyes to look straight ahead when we
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Fig. 1.10: Non-optic reflex system pathway LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLFMedial longitudinal fasciculus; VN- Vestibular nucleus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuron pathway
have tilted our head to the left the eyes will move to the right. Try this on yourself by tilting your head to the left. You will note your eyes move to the right so that you keep on looking straight ahead. When the semicircular canal is stimulated, impulse goes to the same side (in this case left side) vestibular nucleus. From the left vestibular nucleus, impulses go to the opposite side pontine gaze center which in turn send impulses to the right VI nerve nuclei and left III nerve nucleus. This is the supranuclear pathway. Then the infranuclear
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pathway takes over to the right lateral rectus and left medial rectus and the eyes turn towards the right. This constitutes the vestibular influence on eye movements. Neck Receptors Contributory information also comes from the proprioceptive organs of the neck muscles via the spinovestibular tract. Cerebellum The role of the cerebellum is not very clear. There is a prominent flocculo-oculomotor tract, which is the only direct cerebellar connection with the eye nerve nuclei. This pathway connects with the opposite III nerve nuclei and the same side VI nerve nuclei (exactly opposite the semicircular canal connection, which connects with the same side III nerve and opposite side VI nerve nuclei). Thus, the eyes tend to move in the opposite direction. This pathway may help explain the reason why nystagmus in cerebellar disease is in the opposite direction to that occurring in vestibular disease. POSITION MAINTENANCE SYSTEM The function of the position maintenance system is to maintain an object of interest on the fovea or to maintain a specific gaze position. It is the most complex of eye movements and works efficiently only when the person is alert. It becomes seriously disturbed when the person’s level of consciousness is depressed. The micromovement systems use the same substrates as its macrocounterparts, but the details of the pathways are not yet known. The micro eye movements are known as microsaccades or flicks and micropursuits or drifts. The microsystem is continuously active in maintaining the target precisely on the fovea, presumable while other eye movement systems are active as well. Hence, it is the ultimate monitor of eye movements, coordinating all the other eye movement systems and determining the precise position of the eye with respect to the target as well as to the head and body. Stated simply, when an object moves more rapidly than the smooth pursuit system can follow it, a saccadic compensation is made to maintain the eye position relative to the moving target. The pursuit system has been overcome by the position maintenance system. Take an example of your catching a ball. At that time when the ball is in the air, your saccadic and pursuit systems work so that your
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eyes are on the ball. Sometimes, there would be an overshooting of either of the systems and at that time the micromovements of microsaccades and micropursuits take over so that you finally catch the ball. SUMMARY Thus, there are basically five supranuclear pathways, which control eye movements. It is important to know them if one wants to understand supranuclear lesions. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Supranuclear Disorders of Eye Movements Athiya Agarwal, Amar Agarwal
INTRODUCTION If paralysis of an eye muscle occurs due to a lesion in the muscle, nerve or the nerve nucleus, all the functions of the muscle are involved. For example, if an infranuclear lesion occurs in the medial rectus, the patient will neither be able to adduct the eye nor be able to perform convergence as the medial rectus is paralyzed. If the lesion was a supranuclear lesion, then the patient would not be able to perform convergence but would be able to adduct the eye. The supranuclear lesions are lesions above the cranial nerve nucleus.1,2 PSEUDO-OPHTHALMOPLEGIA In supranuclear lesions, only those activities controlled by the particular region involved are impaired and other movements even though carried out by the same muscle remain normal. This paralysis of one type of movement and not of another is called pseudoophthalmoplegia. CLASSIFICATION Depending on the supranuclear pathway, we can classify the supranuclear lesions as: • Saccadic disorders • Pursuit disorders • Vergence disorders • Non-optic reflex system disorders (Flow chart 2.1). SACCADIC DISORDERS Saccadic disorders can in turn be divided into two groups (Flow chart 2.1): • Conjugate palsies • Dissociated palsies.
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Manual of Neuro-ophthalmology Flow chart 2.1: Supranuclear pathway lesions
In dissociated palsies, there is a misalignment of the eyes as the conjugate movements become dissociated, whereas in conjugate palsies both the eyes fail to look in one direction. In dissociated palsies, one eye fails to move in a particular direction, whereas the other eye moves in that direction. CONJUGATE PALSIES Depending on the site of lesion, conjugate palsies can be grouped and classified (Flow chart 2.2). The site of lesion could be in the frontal lobe, basal ganglia, etc. In other words an area subserving the saccadic pathway if involved would lead to conjugate palsies. Lesions of the Frontal Cortex Overactivity Epileptic seizures arising in the appropriate area of the frontal cortex cause what are called frontal adversive attacks. In these episodes, the attack commences with the head and eyes being forcibly deviated away from the discharging frontal cortex. If the left frontal cortex has an overactivity due to a discharging focus and area 8 is involved, the saccadic system overworks and the eyes look to the opposite side that is to the right (Fig. 2.1). The side of the body to which the deviation has occurred may then be involved by focal motor activity and ultimately the attack may progress to a generalized seizure (Fig. 2.2).
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Flow chart 2.2: Conjugate palsies
Fig. 2.1: Frontal lobe overactivity: Frontal adversive seizure LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.LobeOccipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
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Fig. 2.2: Frontal adversive attack Occ.Lobe- Occipital Lobe; Fron.lobe- Frontal lobe; PGC- Pontine gaze center
Unilateral Underactivity Damage to the frontal eye field by a vascular lesion may render the patient unable to look to the opposite side. This deficit is rarely seen as rapid compensation occurs and the eye movements appear to be normal within hours. However, residual evidence may be found in the patient having difficulty in maintaining gaze in that direction or in the development of some nystagmus caused by this weakness when attempting to do so. If the patient is subsequently comatose or anesthetized, the eyes will deviate towards the damaged side of the cortex, because of the unopposed activity of the intact opposite frontal lobe.
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Fig. 2.3: Frontal lobe underactivity Occ.Lobe- Occipital Lobe; Fron.Lobe- Frontal lobe; PGC- Pontine gaze center
If the left side of the frontal area is damaged (Fig. 2.3), the intact area 8 on the right side acts. This in turn pushes the eyes to the left side, in other words, to the side of the lesion. The left hemisphere causes a right hemiparesis and the eyes thus look away from the paralyzed limbs. Bilateral Underactivity Bilateral lesions of the frontomesencephalic pathway cause saccadic palsy in both directions with preservation of pursuit and other eye movements. Bidirectional saccadic palsy necessitates utilization of head movements for refixation. The eyes remain locked on the original object of regard during a rapid head movement. This is called spasm of fixation. Bilateral saccadic palsies could be congenital or acquired. If
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acquired it could be due to multiple sclerosis, Wilson’s disease, Huntington’s chorea or lipidosis. The most striking feature of this condition is the head thrusts utilized to accomplish refixations. The head moves in the direction of the eccentric new target, as there is a saccadic palsy present. When the head moves, the intact vestibulo-ocular system (non-optic reflex system) gets activated and the eyes are driven away from the attempted direction of gaze. So, the patient closes the eyelids thus reducing the vestibulo-ocular reflex gain and so reduces the amount of head thrust required. Head rotation overshoots the intended target, enabling the deviated eyes to fixate upon the object. Lesions of the Basal Ganglia Overactivity The basal ganglia is predominantly concerned with movements in the vertical plane. Overactivity in the basal ganglia leads to the oculogyric crisis. This usually consists of a fixed deviation of the eyes in an upward direction. During this crisis, the patient is incapacitated and any attempt to recover control of the eyes results merely in a feeble jerky displacement from the position of spasmodic displacement. The head is frequently turned in the same direction as the eyes. This occurs in postencephalitic parkinsonism, posthead injury state, neurosyphilis or brain tumors. Underactivity: Progressive Supranuclear Palsy In progressive supranuclear palsy there is loss of nerve cells, vascular degeneration’s and glial reactions in the basal ganglia and midbrain. The first manifestation of progressive supranuclear palsy is an inability to make vertical saccades, particularly downward saccades. At this point, the patients bang their shins, eat off only the top part of their plates and complain of being unable to read (they cannot look down!). As the disease progresses, horizontal fast movements become involved as well. Eventually all fast eye movements are affected and the pursuit movements become cogwheel. Lesions of the Collicular Area Parinaud’s Syndrome There are several manifestations of lesions in the collicular area. The signs are thought to be caused by pressure and distortion of
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underlying structures in the midbrain and not by damage to specific pathways traversing the colliculi. The general name for the clinical picture produced is known as Parinaud’s syndrome. Any combination of impaired upward gaze, impaired downward gaze, pupillary abnormalities or loss of accommodation reflex can occur. In general, loss of upward gaze associated with dilated pupils that are fixed to light suggests a lesion at the level of the superior colliculus. Loss of downward gaze, normal pupillary reactions to light and loss of convergence suggest that the lesion is slightly lower in the area of the inferior colliculus. It could be due to lesions of the pineal gland, multiple sclerosis, vascular diseases or Wernicke’s encephalopathy. A special type of nystagmus is present called retractory nystagmus. This is a very rare sign of disease in the collicular area and consists of an inward and outward movement of both eyes when the patient attempts to look upwards. Presumably, it is produced by all the extraocular muscles acting simultaneously—jerking the globe back into the orbit or attempted upward gaze—in an attempt to overcome the inability to look upwards. DISSOCIATED PALSIES In dissociated palsies, one eye moves in one direction whereas the other eye cannot move in the same direction. Thus, there is a dissociation in the gaze movements. These canbe: • Internuclear ophthalmoplegia • One and one-half syndrome • Dissociated vertical palsies. Internuclear Ophthalmoplegia Introduction Lesions affecting the pathways by which the various ocular nuclei are linked together, i.e. lesions of the medial longitudinal fasciculus (MLF) or medial longitudinal bundle produces internuclear ophthalmoplegia. The MLF connects the III nerve and the VI nerve nuclei. If a lesion occurs in this there is prevention of the harmonious coordination of these nuclei in producing conjugate movements. So, one eye carries out a voluntary movement of gaze whereas the other eye does not, thus leading to failure of the conjugate (both eyes moving in the same direction) movement. This leads to a misalignment of the eyes and thus to diplopia. This feature differentiates the internuclear palsies from the other supranuclear lesions.
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Etiology Depending on the lesion being unilateral or bilateral, various causes of internuclear ophthalmoplegia are present (Flow chart 2.3). The common causes are vascular lesions or multiple sclerosis. Classification Internuclear ophthalmoplegia (INO) are grouped into three types. They can be type I, type II or type III INO. Type I-INO In type I INO, the lesion is near the III cranial nerve nuclei including also the convergence area (Fig. 2.4). Essentially there is paralysis of both medial recti. The impulses coming from the pontine gaze center go to the VI nerve and III nerve nuclei. As the connections to the VI nerve nuclei are not affected no disturbance is present in lateral rectus movements. The eyes are divergent due to bilateral involvement of the medial recti and there is loss of convergence. It occurs in hypertensive brainstem lesions and multiple sclerosis. Divergence may be complicated by skew deviation of the eyes in which one eye may be up and out and the other eye looks down and out. There may be a see saw nystagmus present in which the eyes jerk up and down alternately (Fig. 2.5). Type II-INO In this relatively common variety of INO, the MLF is damaged and the medial recti fail to move synchronously with the lateral recti (Fig. 2.6) on attempted lateral gaze to either side. Yet when each eye is tested alone, the medial recti function is evident but incomplete. Test this by covering the abducting eye and making the adducting eye follow the finger. In type II-INO convergence is normal Flow chart 2.3: Etiology of inter nuclear ophthalmoplegia
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Fig. 2.4: Site of lesions in internuclear ophthalmoplegia III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
Fig. 2.5: Type I internuclear ophthalmoplegia
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Fig. 2.6: Type II internuclear ophthalmoplegia
as the convergence area is not affected (Fig. 2.4). This occurs in multiple sclerosis, pontine glioma or in encephalitis. Type III-INO The third variety of INO occurs in multiple sclerosis. In this type of INO (Fig. 2.7), none of the eye abducts completely while adduction is complete. The relay to the VI cranial nerve nuclei is affected on both sides (Fig. 2.4). If you test the eye individually by closing the other eye, the eye would abduct differentiating this from an infranuclear lesion (VI nerve palsy). One and One-Half Syndrome One and one-half syndrome is also known as paralytic pontine exotropia. In the primary position the eye which is opposite the side of lesion is exotropic. The eye on the same side of the lesion looks straight ahead. The lesion is in the pontine paramedian reticular
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Fig. 2.7: Type III internuclear ophthalmoplegia
formation (pontine gaze center—PGC) or VI nerve nucleus and ipsilateral medial longitudinal fasciculus. From figure 2.8 one will understand that only the VI nerve on the side opposite the side of the lesion will work. The patient is not able to gaze with either eye towards the side of the lesion and is not able to adduct the eye on the side of the lesion (Fig. 2.9). This is why this is called one and one-half syndrome as one side gaze is absent and on the other side half the gaze movement only is present. Dissociated Vertical Palsies A dissociated palsy may affect the elevators of one eye in a supranuclear palsy due to a localized lesion close to the nuclei below the point where the corticofugal pathway for elevation of the eyes bifurcates into the branches which go to both III nerve nuclei. In this event,
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Fig. 2.8: One and one-half syndrome- Site of lesion III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
Fig. 2.9: One and one-half syndrome
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conjugate vertical movements are dissociated, one eye being incapable of elevation in voluntary movements but moving up normally in Bell’s phenomenon. PURSUIT DISORDERS Overactivity If there is an overactivity of the parieto-occipital cortex (read vertical pursuit pathway), seizures originating in the occipital cortex cause deviation of the eyes to the same side. But in this situation, the movements will be accompanied by visual hallucinations. These usually consist of flashing lights and colored blobs. A generalized convulsion may ensue but focal motor activity, other than the eye movements is not a feature of a focal seizure arising in the occipital lobe. Underactivity Damage to the parieto-occipital cortex leads to the patient not able to follow a target on the side of the lesion. If the patient has a right occipital lobe lesion, then the patient would not be able to follow the targets to the right side. Damage to the parieto-occipital cortex is often associated with either parietal lobe difficulties, which may make testing impossible. Similarly, if a homonymous hemianopia coexists (as it often does if the lesion is a vascular one), the patient may be unable to follow an object because it keeps vanishing into the hemianopic field. In these cases, it is essential to keep the object to be followed just inside the midline, in the intact half of the patient’s vision and to move it slowly. VERGENCE DISORDERS Paralysis of Convergence Paralysis of convergence occurs if the lesion is in the pretectal area affecting the convergence area (read vergence pathways in Chapter 1). It is characterized by a failure of convergence with crossed diplopia of the concomitant type. When the eyes view a near object, together with the absence of any limitation of movement on either eye inductions or inversions in any part of the field. Paralysis of Divergence Paralysis of divergence is characterized by the appearance of a convergent strabismus with uncrossed diplopia when the eyes view a distant object.
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NON-OPTIC REFLEX SYSTEM DISORDERS Vestibular System Disorders The vestibular apparatus (semicircular canals) controls the non-optic reflex system. Any lesion affecting the semicircular canals, VIII nerve or the vestibular nuclei will seriously affect the push-pull effect of the vestibular control of eye movements. The right-sided vestibular elements, normally push the eyes to the left. If there is a lesion in the right vestibular apparatus, it will lead to weakness of the eye movements to the left side. On attempting gaze to this side, the intact normal vestibular mechanism on the left side, coupled with the weakness of the damaged right side will force the eyes to drift back to the midline. To solve this problem, there will be a quick jerk of the eyes to the left side; i.e. to the side opposite the side of the lesion. The quick jerk in this case will be occurring to the left side and the lesion was in the right side. Nystagmus is always talked in relation to the fast phase of the nystagmus. In this case (right side vestibular lesion), the slow phase was on the right side and to correct it a quick jerk or fast phase occurred towards the left side. Thus, the nystagmus is away from the side of the lesion in a vestibular disease (Fig. 2.10). With destruction of the labyrinth by Ménière’s disease, nystagmus does not occur, because of central compensation for the absence of any input. A similar situation exists after acute labyrinthine destruction when the initial imbalance settles. Similarly, in slowly occurring damage to the VIII nerve (an acoustic nerve tumor) compensation often prevents development of nystagmus. When it does occur in this situation, it reflects brainstem or cerebellar damage from the extension of the tumor into the cerebellopontine angle. With central lesions of the vestibular apparatus (multiple sclerosis, vascular accidents) compensation cannot occur and the nystagmus and associated symptoms of vestibular damage tend to persist. Cerebellar Disorder The exact mechanism of cerebellar nystagmus is not known. When nystagmus occurs it is opposite that found in a vestibular lesion. In a right-sided vestibular lesion, the slow phase of the nystagmus is to the right and the fast phase to the left. This means the nystagmus is to the left, in other words opposite the side of the lesion. In cerebellar disease, the fast phase of the nystagmus is on the same side of the lesion. So, if there is a right-sided cerebellar lesion, the fast phase of
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Fig. 2.10: Vestibular lesion LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.LobeOccipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; VN- Vestibular nucleus
the nystagmus is towards the right side. This could be due to the flocculo-oculomotor pathway, which works in the reverse of the vestibular pathway. The left vestibular pathway pushes the eyes to the right whereas the left flocculo-oculomotor pathway from the left cerebellum pushes the eyes to the left. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Nystagmus Athiya Agarwal, Amar Agarwal
DEFINITION Nystagmus is a rhythmic to and fro oscillation of the eyes. GENERAL CONSIDERATIONS The specific neurophysiologic mechanism of nystagmus is not well understood. Like all eye movements, nystagmus involves all or more of the five known supranuclear pathways1,2 namely: • Saccadic system pathway • Pursuit system pathway • Vergence system pathway • Non-optic reflex system pathway • Position maintenance system pathway. In nystagmus, generally the movement in slow phase is in one direction and the fast phase in the opposite direction. The fast phase of nystagmus is mediated by the saccadic system under all conditions. One or more of the other systems mediates the slow phase. It is important to remember that nystagmus is given its direction based on the fast phase. This means that if we say a nystagmus is to the right, it means that the fast phase of the nystagmus is to the right. But actually, the important point of nystagmus is the slow phase. So actually, nystagmus should be given its direction depending on the slow phase—but this is not done. An abnormality in the slow phase is more significant. But, alas, convention makes us talk only of the fast phase. The eye position at any given moment results from all the impulses fed into the III, IV and VI cranial nerve nuclei, from the supranuclear mechanism, the gaze systems and the gaze centers. Normally the input is balanced and the eye movements are smoothly coordinated. Nystagmus develops when the normal balance is interrupted by a
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change of stimulus in a gaze system, frequently the vestibular system. Thus, in jerk nystagmus, a defect in one system results in eye deviation (slow phase) and repetitive attempts at correction of that deviation (by fast phases). In many kinds of nystagmus, the patient has the subjective experience that the world is moving or oscillopsia. Oscillopsia or perception of motion of the visual field associated with nystagmus seems to be present primarily during the slow phase of nystagmus, during which time the environment appears to move in the direction of the fast phase. You can demonstrate this for yourself by following your finger slowly back and forth horizontally in front of you. Notice that the background appears to move in a direction opposite to your slow eye movement (if the slow phase of nystagmus is to the left, the field appears to move to the right). During saccades (the fast phases of the nystagmus) the background does not appear to move. Try making saccades by looking rapidly from one corner of the room to the other. The background will not be perceived because of an elevated visual threshold. This elevation of visual threshold actually occurs prior to the start of the saccades. Some investigators believe that a discharge associated with the oculomotor activity of the saccade causes an increase of threshold in the visual afferent system. Other evidence suggests that the elevation of visual threshold occurs in the retina as a response to the forms and contour in the visual environment. Environmental motion perceived during nystagmus occurs predominantly during the slow phase, but in a direction that happens to coincide with the direction of the fast phase. Consequently, a patient with a large amplitude right-beating nystagmus (fast phase to the right) might state that the room appears to be moving to the right. During the fast phase of the nystagmus and during all saccades, visual perception is suppressed. TERMINOLOGY Before we proceed further we should understand what certain terms mean in nystagmus. Pendular Nystagmus In this there is an undulatory movement of equal speed and amplitude in both directions.
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Jerky Nystagmus Jerky nystagmus demonstrates a biphasic rhythm wherein a slow movement in one direction is followed by a rapid saccadic return to the original position. Micronystagmus Micronystagmus is a term applied to a nystagmus, which is subclinical, so that it is incapable of being detected with ordinary clinical tests because of its extremely small amplitude. The diagnosis is apparent by the fixation pattern, which shows a regular jerky type of nystagmus with fast and slow phases of extremely small amplitude within the parafoveal areas so that it may be revealed only by a careful examination with the visuoscope or direct ophthalmoscope. Null Zone The field of gaze in which the intensity of nystagmus is minimal is termed the null zone. Neutral Zone It is that eye position in which a reversal of direction of jerky nystagmus occurs and in which any of several bidirectional waveforms, pendular nystagmus or no nystagmus may be present. Alexander’s Law Jerky nystagmus usually increases in amplitude with gaze in the direction of the fast component. This is called Alexander’s law. GRADES Nystagmus is divided into three grades. Grade I Jerky nystagmus is evident only in the direction of the fast phase, i.e. on conjugate deviation to one side. Grade II When in addition, it is evident in the primary position. Grade III When it is evident in all positions of the eyes. EXAMINATION OF A CASE OF NYSTAGMUS There are certain points one should check when one is examining a case of nystagmus. They are:
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Is the nystagmus pendular or jerky? The fast phase of the nystagmus is on which side? Grade of nystagmus Symptoms of nystagmus Is squint present or not and if present, the type of squint? Is the nystagmus affected by heads position? Is the nystagmus worse with the eyes open or with them closed? Is the nystagmus affected by convergence? How wide are the ocular excursions?
CLASSIFICATION Nystagmus can be divided into various groups (Flow chart 3.1). • Ocular nystagmus • Vestibular nystagmus • Cerebellar nystagmus • Central nystagmus • Miscellaneous. OCULAR NYSTAGMUS Ocular nystagmus is due to a defect or embarrassment of central vision, which renders fixation difficult or impossible. It can in turn be either physiological or pathological. The physiological nystagmus can in turn be either deviational nystagmus or optokinetic nystagmus. Flow chart 3.1: Types of nystagmus
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Deviational Nystagmus Deviational nystagmus is also called end-point nystagmus. It is a jerky nystagmoid movement of a physiological type when the fixation of the axes are deviated beyond the limits of the field of binocular fixation and an effort is made to keep them there. It would generally happen if a person looks in the extreme lateral gaze. The fast phase is in the direction of deviation. It would also occur if a person is tired or if there is a paresis of a muscle. Optokinetic Nystagmus Introduction If a target moving in one direction is shown to a person, then the eyes move in the direction of the target and when the target goes out of the limit of gaze, the eyes rapidly comes back to the center to refixate a new target. This is optokinetic nystagmus. Clinical Test A simple way to perform the optokinetic nystagmus (OKN) test is to hold a tailor’s tape in both our hands. One should stand one meter away from the patient. Keep one hand stationary and with the other hand move the tape. The patient looks at the tape. As the tape moves in one direction, the patient follows the movement of the tape by a slow eye movement (pursuit). Then there is a fast eye movement (corrective saccade) to bring back the eyes to refixate on the tape. Kestenbaum’s Newspaper Method The same result can be done with a sheet of a large newspaper moved slowly in front of the eyes in a direction perpendicular to the lines of the newspaper. Barrie’s Ruler Test One can use a ruler about 12 inches long to perform the OKN test. The ruler is held with its long edge horizontal and with its short edge vertical and moved to the right and left of the eye. Optokinetic Nystagmus Drum The best method to test OKN is to use the OKN drum. This is a special drum, which rotates. The drum has black and white stripes painted on it. As the drum rotates the patient fixates on the stripes.
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There is a slow phase towards the direction of movement of the drum and when the stripes go out of the field of view, the eyes have a fast phase so that they come back to the center and refixate new stripes once again. Pathway Optokinetic nystagmus has two parts: a slow phase (pursuit), and a fast phase (saccadic). Let us imagine a tape or target moving in front of the patient’s eyes from left to right. When the target moves from left to right the eyes fixate the target and the image reaches the retina. From here it goes to the optic nerve, optic chiasma, optic tract and then reaches the right occipital cortex in area 19 (Fig. 3.1). This area subserves the pursuit movements. It is important to note that the
Fig. 3.1: Slow phase of optokinetic nystagmus (OKN) LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.lobeOccipital lobe; Fron.lobe- Frontal lobe; III- III nerve nuclei; VI- VI nerve nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
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occipital areas mediate horizontal pursuit movements to the ipsilateral side. In other words, the right occipital lobe mediates horizontal pursuit movements to the right. From the occipital lobe, impulses go to the same side pontine gaze center. In this case, the impulses from the right occipital lobe go to the right pontine gaze center. From here impulses go to the right VI nerve nucleus and the left III nerve nucleus. Till here is the supranuclear pathway. From the right VI nerve nucleus and the left III nerve nucleus impulses go via the infranuclear pathway to the lateral rectus and the medial rectus. Thus, the patient’s eyes move in the direction of the target. When the moving target goes away from the field of vision the eyes which were moving slowly to that side have to come back to their original position. A fast eye movement does this, in other words a saccade. This is the corrective saccade. If a stream of cars are going in front of our vision, then we keep on following one car and when it goes out of the field of vision our eyes would come and fixate back to the car in the center of our field of vision. This would be done by the corrective saccade. As the impulses from the target moving to the right reaches the occipital lobe (area 19) and the object is going out of the field of vision, the occipital lobe sends impulses to the ipsilateral frontal lobe to perform the corrective saccade. In this case the right occipital lobe (Fig. 3.2) sends impulses to the right frontal lobe (area 8). This means there has to be a communication between the occipital lobe and the frontal lobe. From the right occipital lobe impulses pass to the frontal lobe via the parietal lobe. From the right frontal lobe, impulses then pass to the left pontine gaze center which in turn sends impulses to the left VI nerve nucleus and the right III nerve nucleus. This is the supranuclear pathway. Then, the infranuclear pathway takes over and impulses got to the respective lateral and medial recti and the eyes move to the left as a fast eye movement. This is the corrective saccade. One can illustrate this with an optokinetic drum, which is a drum with black and white stripes. The drum is rotated and the eyes fixate on it. When the stripes go away from the field of vision, the corrective saccade occurs. This leads to a type of nystagmus known as optokinetic nystagmus. Parietal Lobe Lesion If the person has a parietal lobe lesion, then there is a problem (Fig. 3.3). When the corrective saccade has to work the impulse would not
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Fig. 3.2: Fast phase of optokinetic nystagmus (OKN) LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.lobeOccipital lobe; III- III nerve nuclei; VI- VI nerve nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
Fig. 3.3: Parietal lobe lesion LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.lobeOccipital lobe; Fron.lobe- Frontal lobe; III- III nerve nuclei; VI- VI nerve nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
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pass beyond the parietal lobe. Thus, this would lead to a deficit in the corrective saccade. So a deep parietal lobe lesion causes loss or decrease of the fast phase of the OKN, when movement of the drum is towards the side of the lesion. Type of OKN Abnormalities There are four types of OKN abnormalities from type I to type IV (Table 3.1). The problems in OKN could occur if the lesion is in the pursuit system starting from the retina, optic nerve to the occipital lobe or in the saccadic system. There also could be a combination of both systems involved. Inverse OKN An inverse OKN, wherein in horizontal movements the more rapid excursion occurs in the direction of the moving object, can be seen in cases of congenital nystagmus of ocular origin or in amblyopic Table 3.1: Types of optokinetic abnormalities Features
Type I Slow phase abnormality
Type II fast phase abnormality
Type III Combination (I and II)
Type IV complex
Pursuit Saccade
Affected Normal
Normal Affected
Affected Normal
Normal Normal
Neuroanatomic correlation
Posterior hemispheric lesions on side of OKN abnormality
Frontomesencephalic lesion on side of OKN deviation
Extensive deep hemispheric lesion on side of SOK abnormality
Occipital lesion on side of OKN abnormality. Disconnection syndrome possible involving splenium of the corpus callosum
Frequently associated signs contralateral to lesion
Hemianopia
Hemiparesis
Hemianopia, Hemiparesis
Hemianopsia
Ocular deviation
Normal
Eyes tonically deviated in direction of moving targets
Same as type I
Same as type I
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nystagmus. The inversion is due to the fact that a pre-existing nystagmus takes precedence over the optokinetic phenomenon and may thus augment it or interfere with it. Pathological Ocular Nystagmus Amaurotic Nystagmus Nystagmus of pendular or rarely jerky type may occur in those who have been blind for a long time. The nystagmus is sometimes constant and at other times it appears only when the attention is aroused. Amblyopic Nystagmus This is due to a defect in central vision in both eyes, which precludes the normal development of the fixation reflex. Spasmus Nutans In this the nystagmus occurs with head nodding. It is also called Dunkel nystagmus. It generally occurs within the first year of life. The cause appears to be difficulty in maintaining fixation, which is frequently associated with inadequate light. There is also insufficient control due to instability of the motor cortical centers in early life. Miner’s Nystagmus This is an acquired occupational disease of the nervous system with special manifestations in the ocular motor apparatus, occurring in workers in coalmines (Fig. 3.4). Basically it is due to lack of illumination. In the early stages which is the latent stage slight nystagmus starts. Then in the acute stage trembling of the head and hands occurs with marked nystagmus and a pathognomic attitude of the head being thrown back. Then the psychopathic stage starts in which there are cramps, tremors, headaches and insomnia. The nystagmus is generally pendular in type in the primary position but frequently changes to the jerky type on lateral gaze. The treatment of this condition is to give the patient surface work and improve the general health. Latent Nystagmus In this condition, nystagmus is not normally present when both eyes are open but is elicited on covering either eye. In the classical case the nystagmus appears on closing one eye. Bilateral jerky nystagmus is
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Fig. 3.4: Miner’s nystagmus
seen with the fast phase towards the uncovered eye. Another condition is called manifest latent nystagmus, which occurs in patients with amblyopia or strabismus who although viewing with both eyes open are fixing monocularly. Again the fast phase is towards the direction of the intended viewing eye. The phenomenon of latent nystagmus is particularly evident when the visual acuity of the two eyes are unequal. Sometimes if one eye has a very poor vision on covering the better eye instead of nystagmus, a conjugate deviation of both eyes occurs towards the side of the closed eye. This is called—the latent deviation of Kestenbaum. One is not sure of the reason for latent nystagmus. It could be due to lack of coordination of the supranuclear centers. It could also be due to the fact that the nystagmus was latent but kept in check by convergence so that abolition of the impulse to binocular convergence allowed it to become manifest.
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VESTIBULAR NYSTAGMUS Vestibular Apparatus The semicircular canals are three fine tubes arranged in the ear. The lateral semicircular canal is tilted up 30 degrees. Normally the eyes at rest are in the primary position (Fig. 3.5). Impulses go from each semicircular canal to the respective vestibular nuclei. From here, the impulse goes to the opposite pontine gaze center, which in turn connects to the same side VI nerve nucleus and opposite side III nerve nucleus. The impulses thus reach the medial and lateral recti and the eyes are balanced and in the primary position. Caloric Test The most easily understood form of vestibular nystagmus is when performing the caloric test. The patient lies on a couch with the head
Fig. 3.5: Caloric test – eyes at rest in primary position LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nerve nuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
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back at 60 degrees to bring the lateral semicircular canals to the vertical position. This is because it is easier to produce convection currents in a vertical column of fluid. The test should not be performed if the eardrum is perforated. Water is taken at 30 degrees centigrade and 44 degrees centigrade. Normal temperature is 37 degrees centigrade. One takes the water at 7 degrees centigrade higher and lower than the normal temperature. The water is run into each ear in turn. A thermostat is used to keep the temperature steady. 250 ml of water is allowed to flow over 40 seconds in the standardized test. While the water is running the patient looks at a point straight ahead. This produces vertigo and easily observed nystagmus as the canals are stimulated or inhibited and the eyes are pushed or pulled on either side. The duration of the nystagmus is timed. The normal duration is 2 minutes and 15 seconds. When warm water is passed in the left ear (44°C), it stimulates the left semicircular canal. This in turn increases the discharge to the left vestibular nucleus and thus the right pontine gaze center. This in turn leads to the eyes deviating to the right (Fig. 3.6). The slow phase of
Fig. 3.6: Caloric test with warm water LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nerve nuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
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nystagmus is thus away from the ear, which is irrigated with warm water. The eyes try to come back to the original position with a fast phase towards the left and thus a vestibular nystagmus is created. When cold water (30°C) is passed through the left ear impulses are inhibited in that side. So the normal right semicircular canal works and pushes the eyes with a slow phase to the left (Fig. 3.7). The fast phase then occurs to the right. Remember nystagmus is always talked of in regard to the fast phase. A mnemonic to remember the direction of the fast phase in the caloric test is—COWS (cold opposite, warm same). This means cold water calorics produce a fast phase to the opposite side and warm water calorics produce a fast phase to the same side. Vertical Vestibular Nystagmus Vertical vestibular nystagmus can be elicited by bilateral caloric stimulation with the patient recumbent and his or her head flexed 30 degrees above the horizontal plane. Bilateral cold water calorics produce vertical nystagmus with the fast phase up and the slow phase
Fig. 3.7: Caloric test with cold water LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nerve nuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
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down. Bilateral warm water calorics produce vertical nystagmus with the fast phase down and the slow phase up. The mnemonic to remember this is: Cold Slows Things Down. This means that the cold water produces the slow phase in the downward direction. Lesions Vestibular nystagmus could be produced with either a central lesion or a peripheral lesion. It is very important to differentiate between the two. The caloric test can differentiate between canal paresis (peripheral lesion) and directional preponderance (central lesion). Canal Paresis (Peripheral Lesion) If the semicircular canal or the VIII nerve are damaged an incomplete or defective response to both hot or cold water in the affected ear will be found. In a normal caloric response (Fig. 3.8) hot and cold water produce a nystagmus for about 2 minutes. If the patient has a left canal paresis (Fig. 3.9) then neither hot nor cold water will produce a good nystagmus in the affected ear. The duration of the nystagmus
Fig. 3.8: Normal caloric response
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will be less, for example, it could be just 1 minute. In peripheral lesions, the nystagmus is unidirectional and is horizontal and not vertical. It is enhanced by removal of ocular fixation and may be positional. Directional Preponderance (Central Lesion) The central connections of the vestibular nerve are such that cold water in one ear has the same effect as hot water in the other. If it is found that nystagmus cannot be induced to one side it indicates that the vestibular nucleus of the appropriate side is defective (Fig. 3.10). This is known as directional preponderance. In left directional preponderance both the stimuli necessary to produce nystagmus to the right fail, that means cold in the left ear and hot in the right ear. This proves that the nerve endings are normal but the brainstem mechanism for gaze to the left is defective. Central vestibular nystagmus is bidirectional and is not influenced by removal of ocular fixation. There is likely to be associated saccadic and pursuit eye movement disorders.
Fig. 3.9: Left canal paresis. Neither hot nor cold stimuli produce a full effect in the left ear, i.e. local lesion
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Fig. 3.10: Left directional preponderance. Both the two stimuli necessary to produce nystagmus to the right fail, that means cold in the left ear and hot in the right ear. This proves that the nerve endings are normal but the brainstem mechanism for gaze to the left is defective
There are some situations in which both canal paresis and directional preponderance may be combined. This is often encountered when an acoustic nerve tumor or other posterior fossa lesion is displacing the brainstem. Rotational Nystagmus Rotation of the head can also produce a rotational nystagmus. If a lateral semicircular canal is stimulated, the vestibular system starts to work. If the head is rotated to the left (Fig. 3.11), the left lateral semicircular canal is stimulated. If we tilt our head to the left, the eyes should generally keep looking straight ahead (the ultimate aim of the whole process). For the eyes to look straight ahead when we have tilted our head to the left the eyes will move to the right. Try this on yourself by tilting your head to the left. You will note your eyes move to the right so that you keep on looking straight ahead.
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Fig. 3.11: Rotational nystagmus LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nerve nuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
When the semicircular canal is stimulated, impulse goes to the same side (in this case left side) vestibular nucleus. From the left vestibular nucleus, impulses go to the opposite side pontine gaze center which in turn sends impulses to the right VI nerve nuclei and left III nerve nucleus. This is the supranuclear pathway. Then the infranuclear pathway takes over to the right lateral rectus and left medial rectus and the eyes turn towards the right. This constitutes the vestibular influence on eye movements. On cessation of the rotation the right semicircular canal takes over producing a deviation of the eyes to the left. Thus, the slow phase is to the left and this is the postrotational nystagmus (Fig. 3.12). Remember when we use the direction of nystagmus, it is always said according to its fast phase.
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Fig. 3.12: Postrotational nystagmus LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nerve nuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus
Doll’s Head Phenomenon The rotational nystagmus provides a simple method for testing vestibular responses in an infant or comatose patient. If an infant or comatose patient is held at arm’s length and the head tilted slightly towards the examiner and rotated to the patient’s left, the infant will develop a slow tonic deviation to the right and a corrective saccade to the left. This is the doll’s head phenomenon. This is extremely helpful in confirming the diagnosis of congenital oculomotor apraxia in infants. In this disorder, the saccadic mechanism is defective. During rotation of the head, the child will have the slow phase movement of the eyes opposite the direction of rotation of the head, but the eyes will not have a fast phase saccadic return. If you are not able to perform the caloric test in your office, you could ask the adult patient to spin around several times while you
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note the postrotational nystagmus when the spinning is stopped. The normal patient who is spun to the left will develop postrotational nystagmus to the right once the spinning is stopped. In other words the slow phase will be towards the left and the fast phase towards the right. The environment will appear to move in the direction of the fast phase. CEREBELLAR NYSTAGMUS The exact mechanism of cerebellar nystagmus is not known. When nystagmus occurs it is opposite that found in a vestibular lesion. In a right-sided vestibular lesion, the slow phase of the nystagmus is to the right and the fast phase to the left. This means the nystagmus is to the left, in other words opposite the side of the lesion. In cerebellar disease, the fast phase of the nystagmus is on the same side of the lesion. So, if there is a right sided-cerebellar lesion, the fast phase of the nystagmus is towards the right side. This could be due to the flocculo-oculomotor pathway, which works in the reverse of the vestibular pathway. The left vestibular pathway pushes the eyes to the right whereas the left flocculo-oculomotor pathway from the left cerebellum pushes the eyes to the left. CENTRAL NYSTAGMUS In central nystagmus, the nystagmus is of the jerky type. It is occasionally present when the eyes are at rest, but usually develops only when they are deviated to one or the other direction. The nystagmus is symmetrical. This means that the movement starts at the same angle of eccentricity and has approximately the same excursion whether the gaze is directed to one or the other side. MISCELLANEOUS Voluntary Nystagmus Voluntary nystagmus is habit learned and retained. The movements are pendular and minute and in a horizontal direction. Hysterical Nystagmus Hysterical nystagmus is just like voluntary nystagmus but the oscillations are quicker.
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Idiopathic Congenital Nystagmus In this there is congenital nystagmus without any known cause. This includes all forms of nystagmus noted at birth or within the prenatal period. It is usually horizontal but may be vertical, circular or elliptical. It may be pendular or jerky. Certain important points about congenital nystagmus are: • It is binocular and there is similar amplitude in both eyes • There is no oscillopsia and it is abolished in sleep • It is dampened by convergence and increased by a fixation effort. As it is dampened by convergence the child usually has good near acuity and can do well in school • It is uniplanar. This is the hallmark of congenital nystagmus. Plane of the nystagmus, usually horizontal remains unchanged in all positions of gaze including the vertical gaze. This phenomenon is seen only in three entities—congenital nystagmus, peripheral vestibular nystagmus and periodic alternating nystagmus • One can frequently identify a null zone of gaze in which the nystagmus is least marked and the visual acuity is the best • The patient may manifest a head turn to keep the eyes in the null zone or alternatively have a muscle surgery to create the same effect • High astigmatism is frequently found which can be treated by contact lenses. Nystagmus Blockage Syndrome In this there is reduction of nystagmus or blockage of the nystagmus in some particular gaze. The nystagmus diminishes or disappears with the willed act of forced convergence while fixating a distant target. This should not be confused with the dampening of congenital nystagmus during convergence on a near target. SYMPTOMS The various symptoms of nystagmus are oscillopsia, diplopia, tilting of the head or head nodding. TREATMENT The treatment can be treating the cause, use of prisms or surgery in which Faden’s operation is done. The methods to treat nystagmus are shown in flow chart 3.2. The treatment can be general treatment where the cause is treated or specific treatment, which can be medical
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Flow chart 3.2: Treatment of nystagmus
or surgical. In medical treatment one can improve the visual acuity by using prisms base out to simulate fusional convergence. One can use prisms to eliminate anomalous head postures also. For a head turn to the left, the neutral zone is in dextroversion and a prism base out before the right eye and base in before the left eye will shift the eyes conjugately along with the neutral zone towards the primary position. One can also use occlusion in which partial occlusion of the sound eye with a neutral density filter to decrease visual acuity in the fixating eye to a level below that of the amblyopic eye but not dark enough to elicit the nystagmus is used. Surgically one can perform Faden’s operation in which the required muscle creating the nystagmus is sutured to the sclera at the equator. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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The Pupil Athiya Agarwal, Amar Agarwal
NORMAL PUPIL The pupil is an aperture present in the center of the iris and controls the amount of light entering the eye and reaching the retina. There is generally only one pupil but in some cases one can have more than one pupil and this condition is called polycoria. PUPILLARY PATHWAYS Introduction When light is shone in one eye, both the pupils constrict.1,2 Constriction of the pupil to which light is shone is called direct light reflex and that of the other pupil is called consensual (indirect) light reflex. If both pupils are illuminated simultaneously, the response summates. This means the constriction of each pupil is greater than the constriction noted when only one pupil is illuminated. Rods and cones initiate the light reflex. Pupilloconstrictor Light Reflex Pathway Afferent The outer segments of the rods and cones are the receptors for both the visual pathway and the light reflex. When light is flashed on the eyes, the pupillary fibers run in the optic nerve. From there they cross in the optic chiasma and reach the optic tract (Fig. 4.1). From the optic tract they leave the visual pathway fibers (which continue to the lateral geniculate body) and reach the pretectal nucleus. This is an ill-defined collection of small cells anterior to the lateral margin of the superior colliculus. Internuncial fibers connect each pretectal nucleus with the
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Fig. 4.1: Pupilloconstrictor light reflex pathway
Edinger-Westphal nucleus of both sides. Half of the postsynaptic fibers from the pretectal area curve around the periaqueductal gray matter to terminate in the ipsilateral Edinger-Westphal nucleus, while the other half cross, mainly via the posterior commissure to the contralateral Edinger-Westphal nucleus. This connection forms the basis of the consensual light reflex. Any given pretectal neuron behaves functionally as though it receives similar inputs from each eye and projects equally in each Edinger-Westphal nucleus. Efferent Preganglionic parasympathetic myelinated fibers now go to the ciliary ganglion via the third cranial nerve. They leave the III nerve in its branch to the inferior oblique. After reaching the ciliary ganglion they synapse there. Then postganglionic myelinated fibers pass through
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the short ciliary nerves to innervate the sphincter pupillae. Normally, postganglionic fibers are non-myelinated and this is the only exception to this rule. These are the parasympathetic fibers. Sleep Normally, there is a tonic inhibitory input from the cerebral cortex to the Edinger-Westphal nucleus and it is a diminution of this input that results in pupillary constriction during sleep. Functions of the Light Reflex • Pupillary constriction associated with light reflex protects against excessive bleaching of the visual pigments by reducing the amount of light entering the eye. • Light reflex helps in light and dark adaptation. This plays a role in maximizing visual acuity at different light levels. A large pupil will allow more light and so can allow greater acuity in dim illumination. On the other hand, a smaller pupil will limit the aberrations produced by the eye’s refractive system and so can also allow greater acuity. It has been found that at any given light level, the size of the pupil strikes an optimum balance between these two factors. Convergence Near Reflex Pathway Near reflex occurs on looking at a near object. It consists of two components—a convergence reflex and an accommodation reflex. The convergence reflex comprises convergence of the visual axes of the eyes with associated constriction of the pupil. Afferent The afferent starts from the medial recti. This travels centrally via the third nerve to the mesencephalic nucleus of the fifth nerve. From here the impulses travel to the convergence center in the tectal or pretectal region. Internuncial fibers from the convergence center then go to the Edinger-Westphal nucleus (Fig. 4.2). Efferent The efferent pathway is along the third nerve (similar to that of the light reflex). From the III nerve efferent fibers of convergence reflex relay in the accessory ciliary ganglion and from there reach the sphincter pupillae.
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Fig. 4.2: Convergence reflex pathway
Accommodation Reflex Pathway The accommodation reflex consists of increased accommodation and associated constriction of the pupil. Afferent The afferent starts from the retina. Impulses go from the rods and cones to the optic nerve, optic chiasma and optic tract (Fig. 4.3). Fibers then pass to the lateral geniculate body, optic radiation’s and striate cortex. The impulses reach area 19 of the occipital cortex. Internuncial fibers then pass from area 19 to the pontine center via the occipitomesencephalic tract. From the pontine center fibers pass to the Edinger-Westphal nucleus of both sides.
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Fig. 4.3: Accommodation reflex pathway
Efferent From the Edinger-Westphal nucleus the efferent impulses travel along the III cranial nerve and relay in the ciliary and accessory ciliary ganglion. From there the fibers reach the sphincter pupillae. Pupillary Dilatation Pathway The pupillary dilatation starts from the posterior hypothalamus (Fig. 4.4). The pathway is the sympathetic pathway unlike the pupilloconstrictor pathway which is parasympathetic. From the hypothalamus first-order neurons start which reach the ciliospinal center of Budge. These fibers descend uncrossed. This center is located in the intermediolateral cell column of C8, T1 and T2. The second-order neuron starts from the ciliospinal center of Budge. These are the preganglionic fibers and they travel via the inferior and middle cervical ganglion to synapse in the superior cervical ganglion. During this long course the preganglionic fibers are closely related to the apical pleura where they may be damaged by bronchial carcinoma. This is Pancoast’s tumor. They can also be damaged during surgery on the neck.
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Fig. 4.4: Pupillary dilatation pathway
The third-order neurons are postganglionic neurons which arise from the superior cervical ganglion. They ascend along the sympathetic plexus around the internal carotid artery to enter the skull. The fibers then join the sympathetic plexus around the ophthalmic artery. Then they go to the nasociliary nerve (branch of ophthalmic division of the trigeminal nerve) and pass through the ciliary ganglion. They do not synapse in the ciliary ganglion and reach the dilator pupillae via the long ciliary nerves. Darkness Reflex When a person goes from a lighted environment to darkness, the pupils dilate. This dilatation has two causes: the first is simply abolition of light reflex with consequent relaxation of the sphincter pupillae, and the second is contraction of the dilator pupillae supplied by the sympathetic nervous system. The pathways involved in dark reflex
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are presumably the same as those of light reflex, since the dilatation at the end of long light stimulation also involves both relaxation of the sphincter pupillae and contraction of the dilator pupillae. Psychosensory Reflex Psychosensory reflex refers to dilatation of the pupil in response to sensory and psychic stimuli. A large number of differently described reflexes fall into this category. They are not seen in a newborn baby, but appear in the first few days of life, developing fully at the age of six months. Their mechanism is very complex and their pathways have still not been elucidated. It is believed that the mechanism of psychosensory reflexes is a cortical one and the pupillary dilatation results from two components—a sympathetic discharge to the dilator pupillae and an inhibition of the parasympathetic discharge to the sphincter pupillae. PUPIL CYCLE TIME A small beam of light focussed at the pupillary margin induces regular, persistent oscillations of the pupil. These oscillations can be timed with a stopwatch. The period of the average complete cycle is called the pupil cycle time. It is prolonged in optic neuritis and in compressive optic neuropathy. LESIONS OF THE PUPIL There are various lesions, which can occur in the pupil (Fig. 4.5) depending upon the location of the lesion. They are as follows: Amaurotic Pupil Amaurotic pupil is a total afferent pupillary defect (Fig. 4.5). A complete optic nerve or retinal lesion leading to total blindness on the affected side causes it. The eye has no perception of light. The points in an amaurotic pupil are: • The pupil neither reacts to direct light stimulation, nor does it create a consensual light reflex in the opposite eye • When light is shone on the opposite eye, there is a good light reflex in that eye and a good consensual light reflex in the affected eye • This shows that the defect is an afferent defect and the efferent system is normal.
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Fig. 4.5: Lesions of the pupil
Marcus Gunn Pupil Swinging Flashlight Test A Marcus Gunn pupil is a relative afferent pupillary defect. An incomplete optic nerve lesion or severe retinal disease causes it. It is best tested by the swinging flash-light test. To perform this test (Fig. 4.6), a bright flashlight is shone onto one pupil and constriction is noted. Then the flashlight is quickly moved to the contralateral pupil and the response is noted. This swinging to and fro of the flashlight is repeated several times while the pupillary response is observed. Normally, both pupils constrict equally and the pupil to whom light is transferred remains tightly constricted. In the presence of a relative afferent pupillary defect in one eye, the affected pupil will dilate when the flashlight is moved from the normal eye to the abnormal eye.
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Fig. 4.6: Swinging flashlight test
This is a paradoxical response. This is called the Marcus Gunn pupil and is the earliest indicator of optic nerve disease even in the presence of a normal visual acuity. Grades Marcus Gunn pupil can be graded depending on the response to the swinging flashlight test. During the swinging flashlight test, if the amount of light information transmitted from one eye is less than that carried from the fellow eye, the following phenomenon may be noted when the light is swung from the normal eye to the defective eye. Thus Marcus Gunn pupils can be graded. • 3-4 + Marcus Gunn pupil: There is immediate dilatation of the pupil, instead of normal initial constriction • 1-2 + Marcus Gunn pupil: No change in pupil size, initially, followed by dilatation of the pupils • Trace Marcus Gunn pupil: Initial constriction, but greater escape to a larger intermediate size than when the light is swung back to the normal eye.
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Lesion Marcus Gunn pupil sign indicates an asymmetry of conduction and will not be present in symmetric bilateral lesions of the optic nerve or retinal disease. A Marcus Gunn pupil will not occur if the lesion is in the optic chiasma or optic tract as in these areas fibers are present from the opposite eye also. Important Points • There is no such thing as bilateral Marcus Gunn pupil. There may be bilaterally reduced direct response of the pupils to light, resulting in light-near dissociation, but the Marcus Gunn phenomenon requires asymmetry of the afferent light transmission. • Opacities of the ocular media (corneal scar, cataracts or vitreous hemorrhage) will not cause a Marcus Gunn pupillary phenomenon if a strong enough flashlight is used. • Extensive retinal damage will cause a significant Marcus Gunn phenomenon. Wernicke’s Hemianopic Pupil Wernicke’s hemianopic pupil indicates the lesion in the optic tract (Fig. 4.5). In this condition, light reflex is absent when light is thrown on the temporal half of the retina of the affected side and nasal half of the retina of the opposite side. Light reflex is present when the light is thrown on the nasal half of the affected side and temporal half of the opposite side. The patient also has homonymous hemianopia as the lesion is in the optic tract. Argyll Robertson Pupil Lesion A lesion (neurosyphilis) causes it in the region of tectum (Fig. 4.5). The lesion is in the region of the sylvian aqueduct when the fibers from the pretectal nucleus go to the Edinger-Westphal nucleus. An Argyll Robertson pupil occurs when in addition to involvement of the internuncial neurons, there is a disturbance of the normal inhibitory pathways from the reticular activating system upon the parasympathetic Edinger-Westphal subnucleus. The result of this inhibition is excessive parasympathetic activity and small pupils.
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Features • The vision in the affected eye is normal • There is no reaction to light • The near reflex is normal and the pupils react as the convergence and accommodation reflex fibers are not affected. The fibers that mediate the pupillary near response lie ventral to the internuncial neurons that enter the Edinger-Westphal nucleus • The pupils are miotic and irregular • The pupils dilate very poorly with mydriatics. Light-Near Dissociation There are many causes of light-near dissociation. They are shown in Figure 4.5. They are: • Argyll Robertson pupil • Bilateral complete afferent pupillary defect as in bilateral optic atrophy. In these the convergence reflex pathway (Fig. 4.2) is not affected as it starts from the medial recti, so there is a light-near dissociation • Lesions in the pretectal area as once again the near reflex are not affected. This occurs in Parinaud’s syndrome. Pseudo-Argyll Robertson Pupil In this there is third nerve palsy with aberrant regeneration of medial rectus innervation into the sphincter innervation pathway. How to Test for a Pupillary Near Response The near response should be tested in good room light so that the patient’s pupils are midsized and the near object is clearly visible. The patient is given an accommodative target to look at. Watching for convergence helps the examiner judge how hard the patient is trying. Tonic Pupil Damage to the ciliary ganglion or short ciliary nerves (Fig. 4.5) produces the tonic pupil. The features are: • Reaction to light is absent and to near reflex very slow and tonic • Accommodative paresis is present • The affected pupil is larger • It is generally unilateral
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• Cholinergic supersensitivity of the denervated muscle occurs. The normal pupil does not constrict with 0.125 percent pilocarpine whereas the tonic pupil does. It could be due to viral infections affecting the ciliary ganglion like herpes zoster. It could also be due to diabetes or alcoholism. When a tonic pupil is associated with absent deep tendon reflexes in the lower extremities the condition is called Adie’s tonic pupil. The lesion is due to denervation of the postganglionic supply of the sphincter pupillae and ciliary muscle of unknown etiology. It generally occurs in women. The near response of the pupil generally exceeds the light reaction in Adie’s syndrome. The near response is slow and steady and on looking back into the distance it tends to hold the contraction for a few seconds. Thus it is tonic. The reasons for this behavior are not very well understood. The slowness of the tonic pupil might be due to the diffusion of acetylcholine through the aqueous to the supersensitive receptors of the iris sphincter. The near reaction is not spared in Adie’s syndrome—it is restored. Aberrant regeneration of fibers occurs that were originally destined for the ciliary muscle into the iris sphincter. So with every effort to focus the eye on a near object, impulses spill into the sphincter, constricting the pupil. Accommodative fibers in the short ciliary nerves outnumber sphincter fibers by 30 to 1. This means that the ciliary muscle will probably receive appropriate reinnervation, but the odds against the iris sphincter receiving the right fibers are very high. Thus with random regeneration of fibers the power of accommodation is likely to recover, whereas the light reaction will not. At the same time the sphincter is likely to be served by aberrant accommodative impulses that constrict the pupil firmly with every near effort. Hutchinson’s Pupil Hutchinson’s pupil occurs in comatose patients with unilaterally dilated, poorly reactive pupils. It is due to ipsilateral, expanding intracranial supratentorial mass (tumor or subdural hematoma) that is causing downward displacement of the hippocampal gyrus and uncal herniation across the tentorial edge with entrapment of the third nerve. The pupillomotor fibers travel in the peripheral portion of the third nerve and are subject to early damage from compression. This abnormality typically heralds the onset of a III nerve paralysis and is an internal ophthalmoplegia. The appearance of an internal ophthalmoplegia in a patient with a suspected or proven supratentorial mass is an ominous sign and indicates urgent surgical intervention.
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Horner’s Syndrome Introduction In Horner’s syndrome there is a lesion of the sympathetic system. There can be three types—central, preganglionic or postganglionic (Fig. 4.7). The characteristic features are as follows. Ptosis There is mild to moderate ptosis due to paralysis of the Muller’s muscle which is supplied by the sympathetic system. Enophthalmos There can be upside down ptosis also and this is due to weakness of the inferior tarsal muscle. In this there is elevation of the inferior eyelid. This leads to an apparent enophthalmos. Miosis There is moderate miosis due to unopposed action of the sphincter pupillae following paralysis of the dilator pathway. Pupillary reactions are normal to light and near. When the lights are turned off the Horner’s pupil dilates more slowly than the normal pupil because it lacks the pull of the dilator pupillae. This is called dilatation lag.
Fig. 4.7: Horner’s syndrome
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Facial anhydrosis Reduced sweating on the ipsilateral face and neck occurs. This is characteristic of preganglionic Horner’s syndrome. Heterochromia iridis When the sympathetic ocular innervation is interrupted early in life (congenital Horner’s syndrome) the pigment of the iris stroma fails to develop producing heterochromia iridis. Central Horner’s Syndrome This occurs in lesions located between the hypothalamus and the ciliospinal center of Budge (Fig. 4.7). It is due to brainstem vascular lesions or demyelinating lesions. The patient will also have brainstem signs and sudden onset of vertigo. Preganglionic Horner’s Syndrome In this the lesion is located from C8 toT2 and the superior cervical ganglion. In other words, the second-order neurons are affected. This can occur in Pancoast’s tumor of the lung or surgery in the neck. There is anhidrosis of the face and neck as the fibers for sweating come out from the superior cervical ganglion. Postganglionic Horner’s Syndrome The lesion involves the third-order neurons from the superior cervical ganglion to the dilator pupillae. It can occur in cavernous sinus lesions or head trauma. There is ipsilateral vascular headache. Pharmacological Tests for Horner’s Syndrome Cocaine test When 4 percent cocaine is instilled in both eyes, the normal pupil will dilate but the Horner’s pupil will not (Fig. 4.8). All Horner’s pupils, no matter where the defect in the pathway is located, will dilate poorly to cocaine. Thus, cocaine helps in establishing the diagnosis of sympathetic denervation and not in localizing the site of lesion. Hydroxyamphetamine test When 10 percent drops of this drug are instilled into both eyes, in a patient with preganglionic lesion both pupils will dilate whereas in postganglionic lesions, the Horner’s pupil will not. It is because, since the hydroxyamphetamine acts by releasing norepinephrine from the nerve endings at the myoneural junction, so in postganglionic lesions, the drug will have no effect. Adrenaline test or phenylephrine test When either adrenaline 1 in 1000 or phenylephrine 10 percent is instilled in both eyes, the Horner’s pupil due to postganglionic lesion dilates more than the normal pupil because of denervation hypersensitivity.
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Fig. 4.8: Pharmacological tests to localize Horner’s syndrome
Reader’s Syndrome This applies to painful postganglionic Horner’s syndrome. Cluster headaches are present. Raeder’s paratrigeminal syndrome is a term that should probably be limited to the occasional middle fossa mass that produces trigeminal nerve involvement with pain and a postganglionic Horner’s syndrome. PHARMACOLOGY OF THE PUPIL The iris has a sphincter controlled by the parasympathetic system (Fig. 4.9) and a dilator controlled by the sympathetic system (Fig. 4.10). In both the systems acetylcholine is the neurotransmitter at the synapse between the preganglionic and postganglionic neurons. In the parasympathetic system, acetylcholine is the neuroeffector at the sphincter. In the sympathetic system the neuroeffector at the dilator
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Fig. 4.9: Parasympathetic system
Fig. 4.10: Sympathetic system
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is norepinephrine. There are alpha- and beta-sympathetic receptors in the ciliary body. The beta-receptors are inhibitory. Norepinephrine acts only upon alpha-receptors, which are the only receptors present in the dilator muscle of the iris. An iris deprived of postganglionic innervation develops supersensitivity within 24 to 48 hours, i.e. a physiologic response occurs when lesser amounts of cholinergic and sympathetic substances are present than those usually required to cause the same physiologic response. Parasympathetic drugs can be of three types: (i) the directly acting drugs like pilocarpine which act directly on the effector and have the same action as the acetylcholine, (ii) indirect-acting cholinergic agents that interfere with the hydrolysis and degradation of acetylcholine, for example, the anticholinesterase inhibitors like eserine and physostigmine, and (iii) anticholinergic drugs that compete with acetylcholine for receptors at the effector site of the sphincter muscle, such as atropine. Atropine blocks the parasympathetic receptors at the sphincter muscle and prevents the muscle constriction caused by acetylcholine. Sometimes, one has to find out whether a fixed dilated pupil (Fig. 4.11) is due to an interruption of parasympathetic innervation by an anatomic lesion or to pharmacological dilatation of the pupil. The examiner should instill 1 to 2 percent pilocarpine in the affected eye.
Fig. 4.11: Dilated pupil
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If the patient has received an anticholinergic drug that dilated the pupil by blocking the receptor site, the pupil will not constrict. If the pupillary dilatation is due to interruption of the parasympathetic pathways proximal to the neuroeffector junction, the pilocarpine will act directly on the sphincter muscle and will cause pupillary constriction. Sympathetic acting drugs can be directly acting or indirectly acting drugs. The directly acting drugs like phenylephrine or epinephrine act directly on the alpha-receptors dilating the pupil. The indirectly acting drugs like cocaine and hydroxyamphetamine (Paredrine) act in a different way. Cocaine causes pupillary dilatation by blocking the normal re-uptake of constantly released norepinephrine. This leads to an accumulation of norepinephrine at the neuroeffector junction. Hydroxyamphetamine acts directly on the neuroeffector junction and causes release of norepinephrine from presynaptic vesicles. The presence of norepinephrine in presynaptic vesicles depends on the integrity of the third-order neuron. The presence of norepinephrine in these vesicles is not impaired by interruption of the preganglionic (second-order) neuron. PUPIL ABNORMALITIES Hippus Hippus is a visible rhythmic but irregular pupillary oscillation, deliberate in time and 2 mm or more in excursion. It has no localizing significance. It occurs in: • Normal person • Presence of total third nerve palsy • Hemiplegia • Multiple sclerosis • Meningitis (acute) • Cerebral syphilis • Myasthenia gravis • Epileptics. Paradoxical Pupillary Reaction In this either: (i) the pupil dilates with near vision or constricts in distant vision, or (ii) the pupil dilates on exposure to light or constricts when the light is withdrawn. It occurs in: • Syphilis • Tumors of quadrigeminal region
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• Sleeping individuals who have taken barbiturates • Trauma. Irregularity of the Pupil Irregularity of the pupil occurs in: • Congenital coloboma of the iris • Operations on the iris—like sector iridectomies • Adherent leukoma as one part of the iris is pulled up to the corneal scar • Peripheral anterior synechiae • Iritis • Glaucoma • Tumors of the iris or ciliary body • Argyll Robertson pupil • Iridocorneal endothelial syndrome • Optic atrophy. Polycoria In this there are more than one pupils present. It occurs in: • Congenital • Surgical—due to a surgical iridectomy • Iridocorneal endothelial syndrome (essential iris atrophy) • Iridoschisis. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Visual Pathway Athiya Agarwal
INTRODUCTION The visual pathway starts from the retina and ends in the cortical areas.1,2 There are basically seven levels through which the visual impulses pass. They are: (i) retina, (ii) optic nerve, (iii) optic chiasma, (iv) optic tract, (v) lateral geniculate body, (vi) optic radiation, and (vii) cortical areas. Retina The end organ of the visual pathway is the neural epithelium of the rods and cones. The first conducting nerve cell or neuron of the first order is the bipolar cell. From the bipolar cells the impulses travel to the ganglion cells (Fig. 5.1). From the ganglion cells to the lateral geniculate body (LGB) is the second-order neuron and from the LGB to the occipital cortex is the third-order neuron. This is done via the optic radiations. In the optic nerve head the peripheral fibers from the retina insert in the periphery of the disk and those from the central retina insert in the center of the disk (Fig. 5.2). Optic Nerve The optic nerve is the second cranial nerve and is about 5 cm in length. It has basically 4 portions (read Chapter 6 on Anatomy of the Optic Nerve). They are: • Intraocular portion • Intraorbital portion • Intracanalicular portion • Intracranial portion.
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Fig. 5.1: Neurons in the visual pathway
Fig. 5.2: Arrangement of nerve fibers in the disk from the retina. The peripheral fibers insert in the periphery of the disk while the central fibers insert in the center of the disk
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Optic Chiasma Definition Optic chiasma is a commissure formed by the junction of the optic nerve. This provides for crossing of the nasal retinal fibers to the optic tract of the opposite side and for passage of temporal fibers into the optic tract of the ipsilateral side. Dimensions It is a flattened oblong band, some 12 mm in its transverse diameter and 8 mm from before backwards. Types Central chiasma This is present in about 80 percent of cases. It lies directly (Fig. 5.3) above the sella, so that expanding pituitary tumors will involve the chiasma first.
Fig. 5.3: Variations of optic chiasma
76 Manual of Neuro-ophthalmology Prefixed chiasma This is seen in about 10 percent of cases. In these cases, the chiasma is present more anteriorly over the tuberculum sellae. In such a situation, the pituitary tumor may involve the optic tracts first. Postfixed chiasma This is seen in about 10 percent of cases. In these cases, the chiasma is located more posteriorly over the dorsum sellae so that pituitary tumors are apt to damage the optic nerve first. Anatomy The optic chiasma lies over the (Fig. 5.4) the diaphragma sellae and is ensheathed in pia surrounded by cerebrospinal fluid. As it lies over the diaphragma sellae, presence of a visual field defect in a patient with a pituitary tumor indicates suprasellar extension. Posteriorly, the chiasma is continuous with the optic tracts. Relations The relations of the optic chiasma (Figs 5.4 and 5.5) are: Anteriorly—are the anterior cerebral artery and their anterior communicating branch. Laterally—is the internal carotid artery, as it passes upwards after having pierced the roof of the cavernous sinus. It lies on each side in contact with the chiasma in the angle between the optic nerve and tract. Laterally too is the anterior perforated substance. The medial root of the olfactory tract lies laterally.
Fig. 5.4: Anatomy of the optic chiasma
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Posteriorly—is the tuber cinereum—a hollow elevation of gray matter situated between the mamillaria bodies behind and the optic chiasma in front. Laterally, it is continuous with the gray matter of the anterior perforated substance. From its inferior aspect the infundibulum, which is a hollow conical process, passes downwards and forwards and through a hole in the posterior part of the diaphragma sellae attaches itself to the posterior lobe of the pituitary gland. The infundibulum is thus in close contact with the posteroinferior part of the chiasma, which it joins at an acute angle. Above—is the third ventricle, in the floor of which the chiasma makes a prominence. Inferior—is the hypophysis (pituitary gland) and under the lateral edge of the chiasma is the cavernous sinus. Optic Tract Definition Each optic tract is a cylindrical band, which runs from the optic chiasma to the crus cerebri.
Fig. 5.5: Relations of optic chiasma
78 Manual of Neuro-ophthalmology Course It runs laterally and backwards from the posterolateral angle of the chiasma between the tuber cinereum (Fig. 5.5) and the anterior perforated substance. Becoming more flattened and strap-like it is united to the upper part of the anterior then lateral surface of the cerebral peduncle (crus cerebri). Relations The course can be divided into three parts: Anterior part In the first section of its course (Fig. 5.5), the optic tract lies superficial on the under aspect of the brain. It runs above the dorsum sellae and crosses the third nerve from medial to lateral. Above is the posterior part of the anterior perforated substance and the floor of the third ventricle while medially is the tuber cinereum. Middle part In the middle region of its course, the optic tract lies hidden between the uncus and the cerebral peduncle (crus cerebri). It is here also the flattening commences to conform to the upper aspect of the uncus. The optic tract here crosses the pyramidal tract, which occupies the middle segment of the basis pedunculi. Nearby, just dorsal to the substantia nigra, are the lemnisci carrying sensory fibers. It thus comes about that a single lesion here can affect vision and also the great motor and sensory roots. Posterior part In the posterior part of its course, the optic tract lies in the depths of the hippocampal sulcus. Below and parallel to it runs the posterior cerebral artery. Roots In the posterior part of its course, the optic tract divides into two roots—the medial root and the lateral root. Medial root The medial root passes to the medial geniculate body. These are not light fibers but commissural auditory fibers between the two medial geniculate bodies, whose course in the white matter is via the optic tracts and chiasma. It is called the Gudden’s commissure. Lateral root This spreads over the LGB and for the most part ends in it. Terminations The fibers of the optic tract coming from the ganglion cells of the retina reach three major destinations. They are: • Lateral geniculate body—for relay to the visual cortex
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• Each pretectal nucleus—as part of the pupilloconstrictor pathway • Superior colliculus—for general reflex responses to light. Lateral Geniculate Body Definition Lateral geniculate bodies (LGBs) are a pair of bodies, which are part of the thalamus and form an end station for all fibers subserving vision in the optic tracts. Shape Oval or cap-like structure. Situation On the posterior aspect of the thalamus. Development During the process of development from lower forms of life, there is a lateral rotation of the LGB as well as changes in its structure. As a result, in man, the original external surface has become ventral. This is of importance as regards the disposition of retinal fibers in the LGB. Parts The LGB is an asymmetrical cone, with a rounded apex to its main bulk or body and an incomplete rim inferiorly. The rim is drawn out laterally as a peak or spur, which is largely responsible for the surface elevation known as the LGB. The anterior part of the rim is observed by the entry of the optic tract (Fig. 5.6). The medial part of the rim is superior to the medial root and is variably responsible for the surface elevation, which appears to lead dorsally into the medial geniculate body. Inferiorly, the nucleus is hollowed; producing a kind of hilum, which also extends onto the dorsal aspect of the nucleus which here, has no rim. The hilum may be represented by a superficial cleft or depression. Relations On coronal section It appears like a peaked cap, the peak projecting laterally.
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Fig. 5.6: Anatomy of the lateral geniculate body (LGB)
On horizontal section It is shown to be related anteriorly with the optic tract which ends therein. Laterally (Fig. 5.7), it is related to the retrolenticular portion of the internal capsule. Medially it is related to the medial geniculate body, posteriorly with the hippocampal convolution and posterolaterally with the inferior horn of the lateral ventricle. On sagittal section It is seen that the fibers of the optic tract divide into two layers: the inferior of these forms the white layer of the hilum; and the superior forms the dorsal portion of the saddle. Between these laminae which form the capsule of the LGB are alternating layers of myelinated fibers and cells which give the body its characteristic appearance. From the dorsal portion of the LGB pass a mass of fibers (which form its peduncle) into the area of Wernicke. This is a small region of myelinated fibers enclosed by the thalamus medially, the internal capsule laterally and the LGB posteriorly. The main constituents of the area of Wernicke are the fibers of the optic radiation. It also contains the vertical temporothalamic fibers of Arnold. Superior Brachium The LGB is connected to the superior colliculus by a slender band called the superior brachium.
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Fig. 5.7: Relations of the lateral geniculate body
Optic Radiations Definition Optic radiation or optic radiation of Gratiolet is a fresh relay of fibers that carry the visual impulses from the LGB to the occipital lobe. Course They pass forwards and then laterally through the area of Wernicke as the optic peduncle, anterior to the lateral ventricle and traversing the retrolenticular part of the internal capsule behind the sensory fibers and medial to the auditory tract. The fibers spread out fanwise to form the medullary optic lamina. Meyer’s Loop The ventral portion of the optic radiation instead of sweeping back into the occipital lobe plunges forwards into the temporal pole before passing backwards as an inferior longitudinal fasciculus of Meyer. This is known as Meyer’s loop (Fig. 5.8). Interference with this loop causes a superior homonymous quadrantic hemianopia.
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Fig. 5.8: Optic radiations and Meyer’s loop
Further Course The optic radiations as they pass back into the white matter of the cerebral hemisphere lie deep to the middle temporal gyrus, so that tumors of this portion of the temporal lobe may give rise to visual defects. The optic radiations end in the occipital lobe in an extensive area of thin cortex in which is the white stria of Gennari. Other Fibers The other fibers in the optic radiations are: • Fibers that pass from the cortex to the LGB and the superior colliculus • Descending nerve fibers passing to the ocular motor nuclei. The Visual Cortex Calcarine Sulcus In man, the visual projection cortex is situated along the superior and inferior lips of the calcarine sulcus (Fig. 5.9). This area is usually called the striate cortex because of the prominent band of geniculocalcarine fibers termed as striae of Gennari, after its discoverer who discovered it in 1776. The striate cortex is also referred to as area 17 of Brodman. The anterior part of the sulcus is called the calcarine fissure and the posterior part is called the postcalcarine fissure. The striate cortex is situated on the inferior and superior lips of the postcalcarine fissure and on the inferior lips of the calcarine fissure.
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Fig. 5.9: Visual cortex
Course of calcarine sulcus The calcarine sulcus is a deep sulcus extending from near the occipital pole. The parieto-occipital sulcus joins the calcarine sulcus at an acute angle a little in front of its middle, dividing it into anterior and posterior portions and forming an Yshaped figure. Cuneus If the lips of the parieto-occipital sulcus and calcarine sulcus are widely separated, it will be seen that although on the surface they appear to be continuous, they are separated from each other by a small buried vertical cuneate gyrus called cuneus. Histology of the Visual Cortex There are six layers of the visual cortex (Fig. 5.10) histologically. From external to internal they are: • Layer I—plexiform lamina • Layer II—external granular lamina • Layer III—pyramidal lamina • Layer IV—internal granular lamina: this in turn is divided into Layer IV A, Layer IV B and layer IV C alpha and Layer IV C beta • Layer V—ganglionic lamina • Layer VI—multiform lamina.
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Fig. 5.10: Histological layers of the cortex
Parastriate Cortex The visual picture from both the eyes unites in the parastriate cortex called area 18. The lips of the lunate sulcus separate area 17 from area 19. Area 18 is buried within the walls of the sulcus and is in between area 17 and area 19. Peristriate Cortex This is area 19. Most of area 19 lies in the posterior parietal lobe but inferiorly it forms part of the temporal lobe. In area 19 the object seen is recognized. LOCALIZATION IN THE VISUAL PATHWAY Retina The nerve fibers converge towards the disk on the temporal side in the important papillomacular bundle. There is no overlap between the upper and lower halves of the fibers of the peripheral parts of the retina. In the retina the line dividing nasal from temporal fibers, in the sense of those that will cross the chiasma and those that will not, passes through the center of the fovea. Hence, the temporal macular
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fibers remain on the same side while the nasal ones cross. The upper temporal retinal fibers are separated from the lower by the macular fibers—an arrangement, which holds throughout the central visual pathway. Optic Nerve In the optic nerve head In the optic nerve head the arrangement of the nerve fibers is exactly as in the retina. In the optic nerve just behind the eyeball Here the nerve fibers are distributed like in the retina (Fig. 5.11). The upper temporal and lower temporal fibers which are situated on the temporal half of the optic nerve and are separated from each other by a wedge-shaped area occupied by the papillomacular bundle. The upper and lower nasal fibers are situated on the nasal side. In the optic nerve near the chiasma Here the macular fibers are centrally placed (Fig. 5.11).
Fig. 5.11: Arrangement of visual fibers in the optic nerve and tract
86 Manual of Neuro-ophthalmology Optic Chiasma The Nasal Fibers The nasal peripheral fibers constitute about three-quarter of all the fibers and cross over to enter the medial part of the opposite optic tract in the following manner. The lower nasal fibers in the optic nerve traverse (Fig. 5.12) the chiasma low and anteriorly So they are first affected in the tumors of the pituitary body producing upper temporal quadrantic field defects. These fibers form convex loops called Wilbrand’s knee in the terminal part of the opposite optic nerve therefore ipsilateral blindness due to lesions of the proximal most part of the optic nerve is associated with contralateral field defects. They then cross to the opposite tract and occupy its lower quadrant. The upper nasal fibers of the optic nerve traverse the chiasma high and posteriorly Therefore, they are involved first by lesions coming from above the chiasma, e.g. craniopharyngioma. After crossing they occupy the upper nasal quadrant of the opposite optic tract. Some of these fibers make a loop in the ipsilateral optic tract before crossing.
Fig. 5.12: Arrangement of visual fibers in the optic chiasma UN – Upper nasal fibers; LN – Lower nasal fibers; UT – Upper temporal fibers; LT – Lower temporal fibers; M – Macular fibers
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The Temporal Fibers The temporal fibers from the retina which occupy the temporal half of the optic nerves, remain uncrossed and run backwards in the lateral part of the optic chiasma to reach the dorsolateral part of the optic tract. The Macular Fibers The macular fibers, which occupy the central part at the proximal end of the optic nerve, keep this position in the anterior part of the chiasma. Then the crossing (nasal) macular fibers get separated from the uncrossed fibers and pass as a bundle obliquely backwards and upwards to decussate in the posterior most part of the chiasma, which is related to the supraoptic recess. Lesions here may produce central temporal hemianopic scotoma. Optic Tract In the chiasma, crossed and uncrossed fibers are intermingled and when they reach the optic tract they are rearranged to correspond with their position in the LGB. The macular fibers (Fig. 5.11) occupy area of the cross-section dorsolaterally. The fibers from the lower retinal quadrants are lateral and those from the upper are medial. Lateral Geniculate Body The fibers from the upper part of the retina go to the medial part of the LGB and those from below to the lateral part (Fig. 5.13). The macular area is somewhat cuneiform and is confined to the posterior two/third of the nucleus, broadening towards the caudal pole. The neurons of the LGB go to the visual cortex (Fig. 5.1). The axons of the ganglion cells synapse with the dendrites of the neurons of the LGB. There is a regular point to point localization of the retina in the LGB nucleus, which is also carried from the latter to the visual cortex. The LGB has 6 lamina (1-6). The crossed fibers end in the laminae 1, 4 and 6 (Fig. 5.14) while the uncrossed fibers end in the laminae 2, 3 and 5, in such a way that those from the corresponding parts of the two retinae end in neighboring part of the adjacent laminae. Therefore, the smallest lesion of the retina results in degeneration of three laminae of the LGB in which the retinal fibers end. Hence, the conducting unit in optic nerve fibers is a 3-laminae unit. Since the optic radiations commence from all the six laminae (6-laminae unit), so a lesion in the visual cortex results in degeneration of all the 6 laminae of the LGB.
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Fig. 5.13: Arrangement of visual fibers in the lateral geniculate body and optic radiations
Optic Radiation In the optic radiations (Fig. 5.13), there occurs a temporal rotation of the fibers. So, the upper retinal fibers occupy the upper part of the optic radiations and the lower retinal fibers occupy the lower part of the optic radiations. The macular fibers lie in the central part of the optic radiations separating the upper retinal fibers from the lower retinal fibers. Visual Cortex The visual cortex is also called the cortical retina, since a true copy of the retinal image is formed here. It is only in the visual cortex that the impulses originating from the two retinae meet. There is a point to point representation of the retina in the visual cortex. The right visual cortex is concerned with perception of objects situated to the left of the vertical median line in the visual fields and left visual cortex with the objects situated to the right half. In other words, the right visual cortex receives impulses arising from the temporal half of the right
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Fig. 5.14: Arrangment of the axons of ganglion cells in the lateral geniculate body
retina and nasal half of the left retina. The left visual cortex receives impulses arising from the temporal half of the left retina and nasal half of the right retina. The visual fibers contained in the optic radiations are relayed in the visual cortex in the following manner (Fig. 5.15). Fibers from the macular area relay in an extensive area placed posteriorly in the visual cortex. Fibers from the peripheral retina end anterior to the macular fibers. Those from the upper retina go above the calcarine sulcus. BLOOD SUPPLY OF THE VISUAL PATHWAY Introduction The visual pathway receives its blood supply from the two arterial systems, the carotid and the vertebral connected to each other at the
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Fig. 5.15: Arrangement of visual fibers in the visual cortex
base of the brain by the circle of Willis. The branches of the carotid system which contribute to the blood supply of the visual pathway are ophthalmic artery, small branches of the internal carotic artery, posterior communicating artery, anterior cerebral artery and middle cerebral artery. The arteries of the vertebral systems are cortical, central and choroidal branches from the posterior cerebral artery. Similar to the brain, the visual pathway is mainly supplied by the pial network of vessels except the orbital part of the optic nerve, which is also supplied by an axial system derived from the central retinal artery. Retina Choriocapillaries supply the outer four layers of the retina—the pigment epithelium layer, the layers of rods and cones, external limiting membrane, and the outer nuclear layer. Central retinal artery supplies the inner six layers—outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell layer, nerve fibre layer, and internal limiting membrane. The outer plexiform layer gets dual blood supply from chorio capillaries and central retinal artery. The rational vessels are end arteries. Optic Nerve Read Chapter 6 on Anatomy of the Optic Nerve.
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Fig. 5.16: Blood supply of the visual pathway
Optic Chiasma The vessels may enter the chiasma directly or through the pial plexus. The main blood supply of the chiasma (Fig. 5.16) is through the anterior cerebral artery and the internal carotid artery. • The superior aspect of the chiasma is supplied by branches from the anterior cerebral artery and the anterior communicating artery • The inferior aspect of the chiasma is supplied by branches form the internal carotid artery and the posterior communicating artery. A branch from the ophthalmic artery supplies the anteroinferior margin of the chiasma. The venous drainage of the chiasma is as follows: • The superior aspect of the chiasma is drained by the superior chiasmal vein which ends in the anterior cerebral vein • The inferior aspect of the chiasma is drained by the preinfundibular vein which drains into the basal vein. Optic Tract The pial plexus supplying the optic tract receives contributions from: • Posterior communicating artery • Anterior choroidal artery • Branches from the middle cerebral artery.
92 Manual of Neuro-ophthalmology Though there is no anastomosis, there is considerable overlapping in the blood supply of the optic tract by the anterior choroidal artery and the branches of the middle cerebral artery. Therefore, occlusion of the anterior choroidal artery does not result in hemianopia. The venous drainage from the superior aspect of the optic tract is through the anterior cerebral vein and from the inferior aspect of the optic tract through the basal vein. Lateral Geniculate Body The blood supply of the LGB is as follows: • Posterior cerebral artery supplies the posteromedial aspect of the LGB and thus nourishes the fibers coming from the superior homonymous quadrants of the retina • Anterior choroidal artery almost solely nourishes the anterolateral aspect of the LGB and thus supplies the fibers coming from the inferior homonymous quadrants of the retina • The region of the hilum, which contains the macular fibers, is supplied by a rich anastomosis from both the posterior cerebral and the anterior choroidal arteries. Venous drainage of the LGB is through the basal vein. Optic Radiations The blood supply of the optic radiations is as follows: • Anterior choroidal artery supplies the optic radiations anteriorly • Deep optic artery (lateral striate artery) which is a branch of the middle cerebral artery supplies the middle part of the optic radiations • Calcarine branches of the posterior cerebral artery and perforating branches from the middle cerebral artery supply the posterior part of the optic radiations as the fibers spread out to reach the visual cortex. Venous drainage from the optic radiations is mainly by the basal vein and in some parts by the middle cerebral vein. Visual Cortex Blood supply of the visual cortex is by: • Posterior cerebral artery supplies the visual cortex mainly through the calcarine artery
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• The terminal branches of the middle cerebral artery supply the anterior end of the calcarine sulcus and the lateral aspect of the occipital pole. At the posterior pole, there exists a rich anastomosis between the posterior and middle cerebral artery. Venous drainage from the medial aspect of the occipital cortex is by the internal occipital vein, which ends into the great cerebral vein of Galen and straight sinus. The superolateral aspect of the cortex drains into the inferior cerebral vein, which ends in the cavernous sinus. LESIONS OF THE VISUAL PATHWAY AND FIELD DEFECTS Optic Nerve Type Field Defects Retinal nerve fibers enter the optic disk in a specific manner (Fig. 5.17). So, nerve fiber bundle defects are of three basic types: Papillomacular Bundle Macular fibers enter the temporal aspect of the disk. A defect in this bundle of nerve fibers results (Fig. 5.18) in one of the following: • Central scotoma—a defect covering central fixation • Centrocecal scotoma—a central scotoma connected to the blind spot (the cecum) • Paracentral scotoma—a defect of some of the papillomacular fibers lying next to but not involving central fixation.
Fig. 5.17: Arrangement of nerve fibers in the retinal
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Fig. 5.18: Papillomacular bundle field defects
Fig. 5.19: Nerve fiber bundle defects
Arcuate Nerve Fiber Bundle Fibers from the retina temporal to the disk enter the superior and inferior poles of the disk. A defect in these bundles (Fig. 5.19) may cause any of the following: • Seidel scotoma—a defect in the proximal portion of the nerve fiber bundle causes a comma-shaped extension of the blind spot called a Seidel’s scotoma
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• Bjerrum, arcuate or scimitar scotoma—this arcuate portion of the field at 15 degrees from fixation is known as Bjerrum’s area • Isolated scotoma within Bjerrum’s area—this is due to a defect of the intermediate portion of the arcuate nerve fiber bundle • Nasal step of Ronne—a defect in the distal portion of the arcuate nerve fiber bundles produces a nasal step of Ronne. Since the superior and inferior arcuate bundles do not cross the horizontal raphe of the temporal retina, a nasal step defect respects the horizontal (180 degrees) meridian. Nasal Nerve Fiber Bundle Defects Fibers that enter the nasal aspect of the disk course in a straight (nonarcuate) fashion. The defect in this bundle results in a wedgeshaped temporal scotoma arising from the blind spot and does not necessarily respect the temporal horizontal meridian. Remember, nerve fiber bundle defects arise from the blind spot and not from the fixation point (Fig. 5.20). They do not respect the vertical meridian but respect the nasal horizontal meridian. If a person has a quadrantic field defect, then check if the field defect originates from the fixation point or from the blind spot. If it originates from the fixation point it is a retrochiasmal lesion and if it originates from the blind spot it is an optic nerve lesion. Other findings to check for an optic nerve lesion is decreased visual acuity, which generally will not occur in retrochiasmal lesions.
Fig. 5.20: Quadrantic field defects – differentiation between retrochiasmal lesion and an optic nerve lesion
96 Manual of Neuro-ophthalmology Optic Chiasma Lesions The following defects can occur in optic chiasmal lesions (Figs 5.21 and 5.22). Bitemporal Hemianopia The nasal retinal fibers including the nasal half of the macula of each eye cross in the chiasma, to the contralateral optic tract. The temporal fibers remain uncrossed. Thus, a chiasmal lesion will cause a bitemporal hemianopia due to interruption of the decussating nasal fibers. Central Bitemporal Hemianopia Macular crossing fibers pass in the posterior part of the chiasma and are related to the supraoptic recess. Lesions here can produce a central bitemporal hemianopia. Junctional Scotoma A central scotoma in one eye with a superotemporal quadrantic defect in the other eye indicates a lesion at the junction of the optic nerve
Fig. 5.21: Lesions in the optic chiasma UN – Upper nasal fibers; LN – Lower nasal fibers; UT – Upper temporal fibers; LT – Lower temporal fibers; M – Macular fibers
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Fig. 5.22: Field defects in chiasmal lesions
(RE in this case) and the chiasma. The lower nasal fibers cross in the chiasma and course anteriorly approximately 4 mm in the contralateral optic nerve. This is Wilbrand’s knee (Fig. 5.12). Then they turn back to join uncrossed lower temporal fibers in the optic tract. A lesion involving the Wilbrand’s knee creates the junctional scotoma. An important gem to remember this is the J Lawton Smith super gem. If a patient comes with poor vision in the right eye, the important eye for visual field examination is the left eye. There may be an upper temporal defect with respect for the vertical meridian, due to involvement of the Wilbrand’s knee. The lesion is now intracranial at the junction of the right optic nerve and chiasma. The field defects constitute a junctional scotoma. Upper Temporal Quadrantic Defects The lower nasal fibers travel low and anteriorly (Fig. 5.12) in the optic chiasma. Thus, pituitary tumors can affect them. Thus, they produce upper temporal quadrantic defects.
98 Manual of Neuro-ophthalmology Lower Temporal Quadrantic Defects The upper nasal fibers travel high and posteriorly. Thus, a lesion from above the chiasma like a craniopharyngioma can produce a lesion here. These produce a lower temporal quadrantic defect. Optic Tract Lesions All retrochiasmal lesions result in a contralateral homonymous hemianopia. In the optic tracts and LGB, nerve fibers of corresponding points do not yet lie adjacent to one another. This leads to incongruous visual field defects. When we use the term congruous it means homonymous hemianopic defects that are identical in all attributes like location, size, shape, depth and slope of margins. Thus in optic tract lesions, there is an incongruous homonymous hemianopia (Fig. 5.23). Lateral Geniculate Body Lesions A lesion in the lateral geniculate body is extremely rare. Two types of defects can occur. They are: • Incongruous homonymous hemianopia • Relatively congruous homonymous horizontal sectoranopia (Fig. 5.23) associated with sectorial optic atrophy. This is due to vascular infarction of the LGB.
Fig. 5.23: Field defects in optic tract and lateral geniculate body lesions
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Optic Radiations and Visual Cortex Lesions Various lesions (Fig. 5.24) can occur in the optic radiations and visual cortex. Depending on the site of lesion, various field defects can occur. Temporal Lobe Lesions Inferior fibers course anteriorly from the LGB into the temporal lobe, forming Meyer’s loop, approximately 2.5 cm from the anterior tip of the temporal lobe. They are separated from the superior retinal fibers, which course directly back in the optic radiations of the parietal lobe. Anterior temporal lobe lesions (Fig. 5.25) tend to produce midperipheral and peripheral contralateral homonymous superior quadrantanopia. This is called a pie in the sky field defect.
Fig. 5.24: Lesions in the optic radiations and visual cortex
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Fig. 5.25: Field defect due to temporal lobe lesions. Anterior temporal lobe lesions of Meyer’s loop produce incongruous midperipheral and peripheral contralateral homonymous superior quadrantanopia. This is a pie in the sky field defect. This case is an example of a right temporal lobe lesion
Parietal Lobe Lesions The superior fibers cross directly through the parietal lobe to lie superiorly in the optic radiations. The inferior fibers course through the temporal lobe (Meyer’s loop) and lie inferiorly in the optic radiations. Thus, there is a correction of the 90 degree rotation of the visual fibers that occurred through the chiasma into the tracts. Parietal lobe lesions (Fig. 5.26) tend to produce contralateral inferior homonymous quadrantanopia as they affect the superior fibers first. Occipital Lobe Lesions Central homonymous hemianopia In the visual cortex, the macular representation is located on the tips of the occipital lobes. A lesion affecting the tip of the occipital lobe tends to produce a central homonymous hemianopia (Fig. 5.27). Macular sparing The macular area of the visual cortex is a watershed area with respect to the blood supply (Fig. 5.16). Terminal branches of the posterior cerebral and middle cerebral arteries supply the macular visual cortex. Only the posterior cerebral artery supplies the visual cortex subserving midperipheral and peripheral fields. A more proximal (not terminal) vessel supplies the area. Therefore, when there is obstruction of flow through the posterior cerebral artery, ipsilateral macular visual cortex may be spared, because of blood supply provided by the terminal branches of the middle cerebral artery. This may be an explanation of macular sparing (Fig. 5.27). However, when there is a generalized hypoperfusion state (e.g. intraoperative hypotension), the first area
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Fig. 5.26: Field defect due to parietal lobe lesions. Parietal lobe lesions affect the superior fibers first and so produce a contralateral inferior homonymous quadrantanopia. This is a case of a right parietal lobe lesion
Fig. 5.27: Field defects due to occipital lobe lesions
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of the visual cortex to be affected is that supplied by terminal branches, the macular visual cortex, resulting in a central homonymous hemianopia. To say the patient has macular sparing at least 5 degrees of the macular field must be spared in both eyes, on the side of the hemianopia. Temporal crescents When we fixate with both eyes and achieve fusion of the visual information gained by both eyes, there is superimposition of the corresponding portions of the visual fields—the central 60 degrees radius of field in each eye. There remains in each eye, a temporal crescent of field for which there are no corresponding visual points in the other eye. This temporal crescent of field, perceived by a nasal crescent of retina, is represented in the contralateral visual cortex, in the most anterior portion of the mesial surface of the occipital lobe along the calcarine fissure. If a patient has a homonymous hemianopia with sparing of the temporal crescent (Fig. 5.27), the patient has an occipital lobe lesion, since this is the only site where the temporal crescent of fibers are separated from the other nasal fibers of the contralateral eye. Riddoch phenomenon This is a rare visual field sign. Riddoch believed that patients with severe field loss from occipital lobe involvement perceive from and movement separately. He postulated that perception of movement recovers before perception of form and that this phenomenon was of some prognostic value for recovery of field. This phenomenon is illustrated in the patient with extensive dense homonymous hemianopia as a result of an occipital lobe lesion. The patient cannot see a large stationary object in the blind field but can see a smaller object, if it is moving. Altitudinal defect Injury to both occipital poles may result in altitudinal field defects. When the upper portions of the visual cortex or posterior radiation are damaged, the resultant field defects are altitudinal with loss of the entire lower field of vision of both eyes. If the lower portion of the lobes are damaged, death usually occurs after intracranial bleeding as a result of laceration of dural sinuses. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Anatomy of the Optic Nerve Athiya Agarwal
INTRODUCTION Optic nerve, or the second cranial nerve is 5 cm in length and has four portions. 1,2 They are: (i) intracranial, (ii) intracanalicular, (iii) intraorbital, and (iv) intraocular portion. Although we speak of the optic nerve, it is very important to realize that it is really no nerve at all, but essentially a fiber tract joining two portions of the brain. The evidence for this is uncontrollable. They are: • It is an outgrowth of the brain • Its fibers possess no neurolemmal cells • It is surrounded by the meninges, unlike any peripheral nerve • Both the primary and secondary neurons are in the retina. COURSE Intracranial Portion The optic nerve ensheathed in pia runs as a flattened band from the anterolateral angle of the somewhat quadrilateral optic chiasma. It runs forwards and laterally and slightly downwards to the optic foramen. Intracanalicular Portion At its entry into the optic canal, it receives a covering of arachnoid mater and since the dura mater is prolonged through the canal as a periosteum, the nerve is in fact from here onwards surrounded by all three meninges and also of course, the cerebrospinal fluid. It traverses the optic canal and enters the orbit.
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Intraorbital Portion As a rounded cord, it now runs forwards and slightly laterally and downwards in a somewhat sinuous manner to allow for ocular movements and is continued into the back of the eyeball. Intraocular Portion It then enters the eyeball just above and 3 mm medial to the posterior pole. RELATIONS Intracranial Portion The nerve lies at first above the diaphragma sellae, which covers the pituitary body. Between the two nerves in front of the chiasma is a triangular space in which is a variable portion of the pituitary, covered by the diaphragma sellae. Above the nerve is the anterior perforated substance, the medial root of the olfactory tract and the anterior cerebral artery, which crosses superiorly to reach its medial side. The internal carotid artery is at first below and then lateral. Intracanalicular Portion The pia forms a sheath closely adherent to the nerve (Fig. 6.1). The dura constitutes the periosteal lining to the canal and at its orbital end splits to become continuous on the one hand with the periorbita and on the other hand with the dura of the optic nerve. The ophthalmic artery crosses below the nerve in the dural sheath to its lateral side. It leaves the dura at or near the anterior end of the canal. Thus, the internal carotid artery is to some extent tied to the dural sheath by its ophthalmic branch and it is also indirectly attached to the optic nerve by the adherence of the sheaths and by branches to the nerve from the ophthalmic artery. Medial to the optic nerve is the sphenoidal air sinus or a posterior ethmoidal sinus, from which it may be separated by a thin plate of bone only. This provides the explanation of retrobulbar neuritis following a sinus infection. Intraorbital Portion At the optic foramen, the nerve is surrounded by the origin of the ocular muscles. The superior and medial rectus are closely adherent to the dural sheath. It is this connection which gives rise to the pain in
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Fig. 6.1: Sheaths of the optic nerve
extreme movements of the globe, so characteristic of retrobulbar neuritis. Between the optic nerve and the lateral rectus are the divisions of the III cranial nerve, nasociliary nerve, sympathetic nerves and the VI cranial nerve. The nasociliary nerve, ophthalmic artery and superior ophthalmic vein cross the nerve superiorly between the nerve and the superior rectus from its lateral to medial side. The ciliary ganglion is lateral to the nerve between the nerve and the lateral rectus. The central retinal artery near the optic foramen, runs forwards in or outside the dural sheath of the nerve. Then it crosses the subarachnoid space to enter the nerve on its under and medial aspect about 12 mm behind the eye. Intraocular Portion The intraocular portion passes through the sclera and choroid and finally appears in the eye as the optic disk (Fig. 6.2). The intraocular portion of the optic nerve head has an average diameter of 1.5 mm,
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Fig. 6.2: Optic nerve head
which expands to approximately 3 mm just behind the sclera, where the neurons acquire a myelin sheath. The optic nerve head may be arbitrarily divided into the following four portions from anterior to posterior. They are: • Surface nerve fiber layer • Prelaminar region • Lamina cribrosa • Retrolaminar region. Surface Nerve Fiber Layer Surface nerve fiber layer is essentially composed of axonal bundles, i.e. nerve fibers of the retina, which converge on the optic disk and astrocytes. The optic disk is covered by a thin layer of astrocytes, the internal limiting membrane of Elschnig, which separates it from the vitreous and is continuous with the internal limiting membrane of the retina (Fig. 6.2). When the central portion of this membrane is thickened, it is referred to as the central meniscus of Kuhnt. All the layers of the retina, apart from the nerve fiber layer, near the optic
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nerve are separated from it by a partial rim of glial tissue called the intermediary tissue of Kuhnt. Prelaminar Region The predominant structures at this level are neurons and a significantly increased quantity of astroglial tissue. The border tissue of Jacoby (a cuff of astrocytes) separates the nerve from the choroid. Lamina Cribrosa It is a fibrillar sieve-like structure made up of fenestrated sheets of scleral connective tissue lined by glial tissue. It bridges the posterior scleral foramina or the scleral canal. The bundles of optic nerve fibers leave the eye through these fenestrations. A rim of collagenous connective tissue with some admixture of glial cells, which intervenes between the choroid and sclera and optic nerve fibers, is called the border tissue of Elschnig. The lamina cribrosa gets its rich blood supply from the circle of Zinn. Retrolaminar Region This area is characterized by a decrease in astrocytes and the acquisition of myelin that is supplied by oligodendrocytes. The addition of myelin sheath nearly doubles the diameter of the optic nerve from 1.5 to 3 mm. The axonal bundles are surrounded by connective tissue septa. BLOOD SUPPLY OF THE OPTIC NERVE Intracranial Part This part of the optic nerve is supplied by the periaxial system of vessels. The pial plexus is contributed by four sources: • Internal carotid artery • Anterior cerebral artery • Ophthalmic artery • Anterior communicating artery. Intracanalicular Part The nerve within the optic canal is supplied by the periaxial system of vessels. The pial plexus in this part is fed mainly by branches from the ophthalmic artery.
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Intraorbital Part The intraorbital part is supplied by two systems of vessels. • The periaxial system—supplying the optic nerve is derived from the 6 branches of the internal carotid artery, namely ophthalmic artery, long posterior ciliary artery, short posterior ciliary artery, lacrimal artery, central retinal artery before it enters the optic nerve and circle of Zinn. • The axial system—supplying the axial part of the optic nerve is derived from the intraneural branches of the central retinal artery, central collateral arteries which come off from the central retinal artery before it pierces the nerve and central artery of the optic nerve. The capillary network for the optic nerve is derived from both the systems. Anastomosis between the two systems has also been demonstrated. Intraocular Part This is the optic nerve head, which has 4 portions: • The surface nerve fiber layer—is mainly supplied by the capillaries derived from the retinal arterioles. These anastomose with vessels of the prelaminar region. Occasionally a ciliary-derived vessel from the prelaminar region may enlarge to form the cilioretinal artery • The prelaminar region—is supplied by vessels of the ciliary region • The lamina cribrosa region—is also supplied by the ciliary vessels which are derived from the short posterior ciliary arteries and arterial circle of Zinn-Haller • The retrolaminar region—is supplied by both the ciliary and retinal circulation with the former coming from the recurrent pial vessels. The central retinal artery provides centripetal branches from the pial plexus and also centrifugal branches. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Oculomotor Nerve Athiya Agarwal
INTRODUCTION The oculomotor (third cranial) nerve is entirely motor in function.1,2 It supplies all the extraocular muscles except the lateral rectus and superior oblique. It also supplies the sphincter pupillae and the ciliary muscle. NUCLEUS The nucleus of the oculomotor nerve lies in the midbrain at the level of the superior colliculus (Fig. 7.1). The oculomotor nucleus complex has two motor nuclei. The main motor nucleus. This is composed of the subnuclei supplying individual extraocular muscles as follows: • Dorsolateral nucleus—ipsilateral inferior rectus • Intermedial nucleus—ipsilateral inferior oblique • Ventromedial nucleus—ipsilateral medial rectus • Paramedial (scattered) nucleus—contralateral superior rectus • Caudal central nucleus—bilateral levator palpebrae superioris. The accessory motor nucleus (Edinger-Westphal nuclei). It is situated posterior to the main oculomotor nucleus mass. It consists of a median and two lateral components. Perhaps the cranial half of the nucleus is concerned with light reflexes and the caudal half with accommodation. The median part is fork shaped (nucleus of Perlia) and its role in convergence is questionable. Important points to remember is that both the LPS are supplied by one central caudal nucleus and each SR is supplied by the opposite III nerve nucleus.
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Fig. 7.1: Third nerve nucleus
EXIT FROM THE BRAIN The nerve starts from the third nerve nucleus (Fig. 7.2) and passes through the red nucleus. It then passes through the corticospinal (pyramidal) tract and emerges from the midbrain and passes into the interpeduncular space (Fig. 7.3). The nerve passes between the posterior cerebral artery and the superior cerebellar artery to reach the cavernous sinus. We should at this stage also understand the relations of the other cranial nerves when they exit from the brain (Fig. 7.3). The IV cranial nerve comes out dorsally and passes between the posterior cerebral and superior cerebellar arteries. The V nerve comes out from the pons. Between the two V nerves is the pons. Lateral to the V nerve is the middle cerebellar peduncle. The VI, VII and VIII nerve come out between the pons and medulla oblongata. The VI nerve comes out at the level of the pyramid (part of medulla oblongata), the VII nerve comes out at the level of the olive (part of medulla oblongata) and the VIII nerve comes out at the level of the inferior cerebellar peduncle (part of medulla oblongata). The IX, X and XI nerves come out between the olive and the inferior cerebellar peduncle and the XII nerve comes out between the olive and the pyramid.
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Fig. 7.2: Pathway of oculomotor nerve
Fig. 7.3: Location of exit of cranial nerves in the brain
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CAVERNOUS SINUS The oculomotor nerve is lateral to the posterior clinoid process and above the attached margin of the tentorium cerebelli. It now lies lateral to the pituitary fossa above the cavernous sinus, then piercing the dura it passes through the roof and comes to lie in the lateral wall of the cavernous sinus (Fig. 7.4). COURSE IN SUPERIOR ORBITAL FISSURE The III cranial nerve now enters the superior orbital fissure (SOF) but just before it does so it divides into a small superior and a larger inferior division. At about this point the IV nerve crosses the III nerve and lies above and then lateral to it. Definition Superior orbital fissure or sphenoidal fissure is an irregularly linear fissure situated in the most posterior part of the orbital cavity between the posterior part of the lateral wall, roof and medial wall of the orbit. Size 2 cm long.
Fig. 7.4: Cavernous sinus
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Shape It is comma shaped or retort shaped (Fig. 7.5). Limbs It comprises two limbs—a narrow lateral part and a wider medial part. Borders Superiorly, the lesser wing of the sphenoid forms the SOF, inferiorly and laterally it is formed by the orbital process of the greater wing of the sphenoid, medially by the body of the sphenoid and the orbital process of the perpendicular plate of the palatine bone. Relations The fissure is obliquely placed and its lower end is continuous anteriorly with the inferior orbital fissure and posteriorly with the pterygomaxillary fissure. Its medial end is separated from the optic foramen by the posterior root of the lesser wing of the sphenoid. Common Tendinous Ring This stretches across or lies across the fissure. It divides the fissure into an upper lateral, middle and lower medial part.
Fig. 7.5: Superior orbital fissure
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Contents Passing above the annulus from medial to lateral is the: • Trochlear nerve • Frontal nerve • Lacrimal nerve • Recurrent meningeal branch of the lacrimal artery • Orbital branch of the middle meningeal artery • The superior ophthalmic vein also passes in this part. Passing within the annulus or between the two heads of the lateral rectus is the following structures from above downwards; • Superior division of the III cranial nerve • Nasociliary nerve • Sympathetic root of the ciliary ganglion • Inferior division of the III cranial nerve • VI nerve. As a rule nothing passes below the annulus, but rarely the inferior ophthalmic vein passes through it. COURSE IN THE ORBIT The superior division inclines medially above the optic nerve and just behind the nasociliary nerve to supply the SR on its undersurface at the junction of the middle and posterior thirds and the LPS. The inferior division immediately divides into three. The branch to the MR passes under the optic nerve to enter the muscle. The branch to the IR pierces the muscle on its upper aspect near the junction of the middle and posterior thirds. The long branch to the IO runs along the floor of the orbit on the lateral border of the IR or between this muscle and the LR. It crosses above the posterior border of the IO about its middle and breaks up into 2 or 3 branches, which enter the upper surface of the muscle. It is this nerve that gives the short stout branch to the ciliary ganglion for relay to the sphincter pupillae and the ciliary muscle. CILIARY GANGLION Introduction Ciliary ganglion is a peripheral parasympathetic ganglion placed in the course of the oculomotor nerve. It lies near the apex of the orbit between the optic nerve and the tendon of the lateral rectus muscle.
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Size It measures about 2 mm anteroposteriorly and about 1 mm in diameter. Color Reddish gray. Shape Polygonal. Roots It receives posteriorly (Fig. 7.6) three so, called roots or rami. Long or Sensory Root Long or sensory root comes from the nasociliary nerve and is given off just after that nerve has entered the orbit. It is a slender nerve about 5 to 10 mm long and passes along the lateral side of the optic nerve to reach the upper and posterior part of the ganglion. It contains sensory fibers from the cornea, iris and ciliary body and possibly sympathetic fibers to the dilator pupillae.
Fig. 7.6: Ciliary ganglion
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Short or Motor Root Short or motor root comes from the nerve to the inferior oblique a few mm beyond the point where the nerve arises from the inferior division of the III nerve. It is much thicker than the sensory root and is about 1 to 2 mm long. It passes upwards and forwards to enter the posteroinferior angle of the ganglion. It carries parasympathetic fibers to the sphincter pupillae and the ciliary muscle. These synapse in the ganglion. Sympathetic Root Sympathetic root comes from the plexus around the internal carotid artery. It passes through the superior orbital fissure within the annulus tendinosus inferomedial to the nasociliary nerve. It lies below and close to the long root with which it may be blended and enters the posterior border of the ganglion between the other roots. It carries constrictor fibers to the blood vessels of the eye and dilator fibers to the pupil. Branches Short Ciliary Nerve The somata of the preganglionic parasympathetic nerve fibers reaching the ciliary ganglion are in the Edinger-Westphal nucleus. They are of course myelinated. They end in the ganglion by forming synapses with the somata and dendrites of the postganglionic neurons. These axons form the short ciliary nerves. They are unique in the fact that normally postganglionic nerve fibers are not myelinated but they are the exception to this rule and are myelinated. The short ciliary nerves contain small groups of displaced ganglion cells. The short ciliary nerves are 6 to 10 in number. They are delicate filaments, which come off in two groups from the anterosuperior and anteroinferior angles of the ganglion respectively. They run sinuously with the short ciliary arteries above and below the optic nerves, the lower group being the larger. As they pass forwards, they connect with each other and with the long ciliaries. Having given branches to the optic nerve and the ophthalmic artery they pierce the sclera around the optic nerve. They run anteriorly between the sclera and the choroid, grooving the sclera, to the ciliary muscle on the surface of which they form a plexus, which supplies the iris, ciliary body and the cornea (Fig. 7.7).
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Fig. 7.7: Supply of short ciliary nerves
BLOOD SUPPLY All nerves are supplied with blood vessels, which are essential for their normal functioning. The arteries supplying a nerve are derived from adjacent vessels, which most often are of a small size. On reaching the nerve the nutrient artery breaks up into ascending and descending branches which anastomose in the epineurium with similar branches from other nutrient arteries. From such epineural vessels, branches penetrate the perineurium where further anastomoses occurs and finally small vessels penetrate into the fasciculi and from there a rich longitudinally disposed capillary network runs up and down the nerve in unbroken continuity. This intrafascicular network is reinforced along its length by contributions from the various nutrient vessels, which reach the epineurium, but no part of the intrafascicular plexus may be regarded as being dominated by any one nutrient artery. In the same way the III, IV and VI cranial nerves get their blood supply. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Lesions of the Oculomotor Nerve Athiya Agarwal
ETIOLOGY The common causes of oculomotor nerve palsy are: neoplasms, trauma, aneurysms, ischemic lesions and others like ophthalmoplegic migraine.1,2 GENETICS Oculomotor nerve palsy could be congenital due to a hereditary cause. The mode of transmission could be either autosomal dominant or recessive. CLINICAL FEATURES Total third nerve paresis may be central, sparing the pupil or peripheral with pupillary involvement. If the pupil is spared, the most likely cause is a vascular lesion. If the pupil is involved, it is most likely due to an aneurysm. The patient has a large exotropia with hypotropia. A fixed dilated pupil is seen. On attempted adduction, the eye intorts as the superior oblique would be normal. Excluding birth trauma, the congenital form of external ophthalmoplegia has certain features—it is generally bilateral and the extraocular muscles can vary in their degree of involvement. One can also get partial paresis as the III nerve divides into a superior and an inferior division. If the superior division of the III nerve is involved, generally other cranial nerves are also involved. One can get an isolated involvement of the inferior division of the III cranial nerve. NUCLEAR THIRD NERVE PARESIS This is extremely rare and occurs if the lesion involves the III nerve nucleus (Fig. 8.1). The important points about this lesion are:
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• Each superior rectus is innervated by the contralateral third nerve nucleus. So, if there were nuclear third nerve palsy on one side then there would be a paresis of the contralateral superior rectus. • Both levator palpebrae superioris are innervated by one subnuclear structure, the central caudal nucleus. Therefore, nuclear third nerve palsy leads to bilateral ptosis. THIRD NERVE FASCICLE SYNDROMES In these cases the III nerve has already left the nucleus, so the lesions affect only one side. There are various syndromes, which can occur depending on the site of lesion (Fig. 8.1). They are due generally to an ischemic, infiltrative (tumor) or rarely inflammatory lesion. Nothnagel’s Syndrome In this case the lesion is in the area of the superior cerebellar peduncle. As the lesion involves the superior cerebellar peduncle the patient has an ipsilateral third nerve paresis with cerebellar ataxia. Benedict’s Syndrome In this syndrome the lesion is in the area of the red nucleus. This leads to contralateral hemitremor with ipsilateral third nerve paresis.
Fig. 8.1: Syndromes of the oculomotor nerve
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Claude’s Syndrome This syndrome has features of both Nothnagel’s and Benedict’s syndrome. Weber’s Syndrome In this the lesion is in the area of corticospinal (pyramidal) tract. This leads to an ipsilateral third nerve paresis with contralateral hemiparesis. UNCAL HERNIATION SYNDROME As the third cranial nerve goes towards the cavernous sinus, it rests on the edge of the tentorium cerebelli. The portion of the brain overlying the third nerve, at the tentorial edge, is the uncal portion of the undersurface of the temporal lobe. A supratentorial spaceoccupying mass located anywhere in or above this cerebral hemisphere, may cause a downward displacement and herniation of the uncus across the tentorial edge, thereby compressing the third nerve. This leads to a dilated and fixed pupil. (Fig. 8.2). This is called the Hutchinson pupil and is the first indication that altered consciousness is due to a space-occupying intracranial lesion. POSTERIOR COMMUNICATING ARTERY ANEURYSM As the third cranial nerve moves towards the cavernous sinus, it travels alongside the posterior communicating artery (Fig. 8.3). If there is an aneurysm of the posterior communicating artery it can lead to compression of the third nerve. This leads to an isolated third nerve paresis with the pupil getting involved.
Fig. 8.2: Hutchinson pupil
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Fig. 8.3: Posterior communicating artery aneurysm
CAVERNOUS SINUS SYNDROME In the cavernous sinus syndrome, there would be third nerve paresis with involvement of other nerves like IV, V and VI cranial nerves. The patients have painful ophthalmoplegia. This could be due to trauma, neoplasms, aneurysms or inflammations. This syndrome can lead to aberrant regeneration of the III cranial nerve. ORBITAL SYNDROME There can be proptosis as an early sign. The V cranial nerve can also be involved but this would involve only the ophthalmic division. PUPIL-SPARING ISOLATED THIRD NERVE PARESIS The pupillomotor fibers travel in the III nerve in the outer layers and are therefore closer to the nutrient blood supply enveloping the nerve. This is the reason why the pupillomotor fibers are spared generally in ischemic third nerve paresis but are affected in compressive lesions like tumors. Ocular myasthenia can mimic a pupil-sparing third nerve palsy, so one can perform the Tensilon test to differentiate the two. ABERRANT REGENERATION OF OCULOMOTOR NERVE Aberrant regeneration of the cranial nerve follows damage of the nerve by trauma or tumor. Lid gaze dyskinesis • Elevation of the lid on adduction (inverse Duane’s sign) • Elevation of the lid on depression (pseudo Von Graffe’s sign)
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Pupil gaze dyskinesis • Constriction on adduction (pseudo Argyll Robertson pupil) • Constriction on depression. If aberrant regeneration occur spontaneously (primary regeneration) without a preceding third nerve palsy usually is caused by a cavernous sinus tumor or aneurysm. As a rule aberrant regeneration never occurs in Ischemic III nerve palsy. MANAGEMENT Occlusion One can occlude the paretic eye for sometime, till the healing occurs and the III nerve paresis is cured. Medical Treatment One can give the patient multivitamin injections and tablets and treat the cause like diabetes or hypertension. Surgical Treatment The surgical management of a complete III nerve paralysis is a difficult job. At the very best, the surgeon will succeed only in moving the paretic eye into the primary position without restoring adduction, elevation or depression to a significant degree. A very good method to treat this condition is to do a tenotomy of the lateral rectus and the superior oblique combined with a transposition of the vertical recti muscles to the insertion of the medial rectus muscle. Even though the treated eye will continue to be immobile, it will at least be centered and this operation should be considered especially in patients who fixate with the paralyzed eye. For the ptosis one should perform a frontalis muscle sling operation. This can be done as a second step. If the patient has a partial palsy with slight medial rectus movement one can perform a maximal recession of the lateral rectus muscle (at least 12 mm) and resection of the medial rectus (at least 7 mm) with upward transposition of the tendons in case of an associated hypotropia. This may restore a small but useful field of vision even though double vision will persist in up and downward gaze. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Trochlear Nerve and its Lesions Athiya Agarwal
INTRODUCTION The trochlear nerve is the fourth cranial nerve is the thinnest and also has the longest intracranial course of about 75 mm.1,2 This is the only cranial nerve that comes out from the dorsal aspect of the brainstem. It is also the only cranial nerve that crosses completely to the opposite side. In other words, the trochlear nerve arises from the contralateral nucleus (Fig. 9.1). NUCLEUS The trochlear nerve nucleus is situated in the midbrain at the level of the inferior colliculus. It is caudal to and continuous with the third nerve nucleus complex. COURSE Exit from the Nucleus From each nucleus, the nerve fibers run laterally and emerge from the dorsal aspect of the midbrain at the level of the inferior colliculus. They pass medially and decussate completely. Thus, the IVth cranial nerve crosses to the opposite side and thus each superior oblique is supplied from the contralateral trochlear nucleus. Exit from the Brain Once the trochlear nerve exits from the brain from the dorsal side it turns towards the ventral side and passes between the posterior cerebral artery and superior cerebellar artery. It then pierces the dura on the posterior corner of the roof of the cavernous sinus to enter into it.
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Fig. 9.1: Trochlear nerve – anatomy
Cavernous Sinus In the cavernous sinus, the nerve runs forwards in the lateral wall lying below the oculomotor nerve and above the first division of the fifth cranial nerve. In the anterior part of the cavernous sinus it rises, crosses over the third nerve and leaves the sinus to pass through the lateral part of the superior orbital fissure. Superior Orbital Fissure The trochlear nerve enters the orbit through the lateral portion of the superior orbital fissure. The nerve passes medially above the origin of the levator palpebrae superioris and ends by supplying the superior oblique muscle through its orbital surface. Orbital Course In the orbit, the trochlear nerve leaves the frontal nerve which is at first close to it at an acute angle and passes medially and forwards
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beneath the periosteum and above the levator palpebrae superioris and superior rectus. It divides up in a fan-shaped manner into 3 or 4 branches, which supply the superior oblique on its upper surface near the lateral border. The most anterior branch enters the muscle at the junction of the posterior and middle thirds and the most posterior some 8 mm beyond its origin. LESIONS OF THE TROCHLEAR NERVE Depending on the level of the lesion, various syndromes can occur with damage to the trochlear nerve. They are as follows: Nuclear Fascicular Syndrome It is difficult to distinguish between nuclear and fascicular lesions due to the short course of the fascicles within the midbrain (Fig. 9.2). It could be due to hemorrhage trauma or demyelination. It is seen with contralateral Horner’s syndrome, since the sympathetic pathways descend through the dorsolateral tegmentum of the midbrain adjacent to the trochlear fascicles.
Fig. 9.2: Lesions of trochlear nerve
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Subarachnoid Space Syndrome As the fourth nerve emerges from the dorsal surface of the brainstem, it can get injured easily. When bilateral fourth nerve palsies occur, the site of injury is likely in the anterior medullary velum. Contracoup forces transmitted to the brainstem by the free tentorial edge may injure the nerves at this site. Other causes could be tumors like pinealoma or tentorial meningiomas. Cavernous Sinus Syndrome If the lesion is in the cavernous sinus, other cranial nerves in close association with the fourth cranial nerve also get involved. Orbital Syndrome In this other cranial nerves close to the fourth cranial nerve are also involved. Other orbital signs like proptosis, chemosis and conjunctival injection are also seen. This could be due to trauma, inflammation or tumors. Isolated Fourth Nerve Palsy Isolated fourth nerve palsy could be due to a congenital cause or it could be acquired. The features of a fourth nerve palsy are: Hyperdeviation The involved eye is higher as a result of the weakness of the superior oblique muscle. One should perform the Bielschowsky’s head tilting test, as when the head is tilted towards the ipsilateral shoulder the hyperdeviation becomes more obvious. Ocular Movements Depression is limited in adduction. Intorsion is also limited. Diplopia Homonymous vertical diplopia occurs on looking downwards. Usually the vision is single as long as the eyes look above the horizontal plane. The patient especially notices diplopia when coming down the stairs. Abnormal Head Posture To avoid diplopia, the head takes an abnormal head posture towards the action of the superior oblique muscle, i.e. the face is slightly turned
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to the opposite side, chin is depressed and the head is tilted towards the opposite shoulder. CHECKING FOURTH NERVE FUNCTION IN THE SETTING OF A THIRD NERVE PARESIS The problem to check the fourth cranial nerve function, if a patient also has a third cranial nerve paresis is that the involved eye cannot be adducted well due to the third cranial nerve involvement. As the eye cannot be adducted, one cannot test the vertical action (depression) of the superior oblique muscle. To solve this problem, first of all we should note a limbal or conjunctival landmark like a blood vessel or pterygium. Then, ask the patient to look down. The patient will not be able to look down as the eye is abducted and not adducted (due to the third nerve involvement). But the eye will intort as the superior oblique works. We should then check from the conjunctival landmark if the eye is intorting. If the conjunctival landmark is moving, the eye is intorting and that means the fourth nerve is intact. BIELSCHOWSKY’S HEAD TILTING TEST The Bielschowsky’s head tilting test can diagnose which muscle is paralyzed. Let us first of all look at a case of R/L hypertropia in which the right eye is at a higher position than the left eye (Fig. 9.3). R/L Hypertropia If the patient has a R/L hypertropia, then it could mean that the right eye is hypertropic in which case the depressors are paralyzed like the RIR or the RSO. It could also mean that the right eye is in the normal position but the left eye is hypotropic. This could be due to the elevators of the left eye being paralyzed like the LIO and the LSR. This is the first step or I step of the test. Out of the extraocular muscles we have narrowed down the diagnosis to four muscles. Now, we perform the II step of the test. In this we ask the patient to perform dextroversion or levoversion. This means we ask the patient to look to the right and to the left. If we ask the patient to look to the right, the right eye could be higher than the left eye. If the right eye is higher on dextroversion, then it could mean that the RIR is involved or it could mean that the left eye is hypotropic. This would be due to a LIO paralysis. In levoversion if the right eye is higher it could be due to a RSO paralysis. Alternately, it could mean that the
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Fig. 9.3: Bielschowsky’s head tilting test for R/L hypertropia
left eye is hypotropic and this would be due to LSR paralysis. Thus, we have narrowed down the muscles from 4 to 2. Finally, we perform the III step in which we tilt the patient’s head to the right and then to the left. If we tilt the head to the right, the right eye will intort and the left eye will extort. This is because nervous impulses will be sent from the semicircular canals to keep the eyes in a straight position. Now, remember the superiors are intorters. So, if the right eye intorts, it means the superiors in that eye (RSR and RSO) work and if the left eye extorts it means the inferiors of that eye (LIO and LIR) work. When this happens in the right eye the RIR will not be used at all as it is an extorter and in the right eye extortion is not taking place. But, in the left eye, extortion will take place and the LIO and LIR will work. Now, the LIO is paralyzed and so cannot work. This will make the LIR only work in that eye and as a balance will not be maintained between these two muscles the left eye will move down as the LIR is also a depressor. Thus, one can diagnose the case of LIO. If we ask the patient to tilt the head to the left, the left eye will intort and the right eye will extort. In the right eye the extorters will
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be the RIR and RIO. Now the RIR is paralyzed and so the RIO will only work and the right eye will move upwards. Similarly, we can differentiate between the RSO and the LSR in the III step. If we tilt the head to the right, the right eye will intort and the muscles that will work are the RSO and RSR. As the RSO is paralyzed the RSR will only work and the right eye will move upwards. If we tilt the head to the left, the left eye will intort and the muscles that will work are the LSR and LSO. If the LSR is paralyzed the LSO will work and the left eye will move down. L/R Hypertropia If we now work on the same principle and get the muscle involved in a L/R hypertropia (Fig. 9.4). If the patient has a L/R hypertropia, then it could mean that the left eye is hypertropic in which case the depressors are paralyzed like the LIR or the LSO. It could also mean that the left eye is in the normal position but the right eye is hypotropic. This could be due to the elevators of the right eye being paralyzed like the RIO and the
Fig. 9.4: Bielschowsky’s head tilting test for L/R hypertropia
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RSR. This is the first step or I Step of the test. Out of the extraocular muscles we have narrowed down the diagnosis to 4 muscles. Now, we perform the II Step of the test. In this we ask the patient to perform dextroversion or levoversion. This means we ask the patient to look to the right and to the left. If we ask the patient to look to the right, the left eye could be higher than the right eye. If the left eye is higher on dextroversion, then it could mean that the LSO is involved or it could mean that the right eye is hypotropic. This would be due to a RSR paralysis. In levoversion if the left eye is higher it could be due to a LIR paralysis. Alternately, it could mean that the right eye is hypotropic and this would be due to RIO paralysis. Thus, we have narrowed down the muscles from 4 to 2. Finally, we perform the III step in which we tilt the patient’s head to the right and then to the left. If we tilt the head to the left, the right eye will extort and the left eye will intort. This is because nervous impulses will be sent from the semicircular canals to keep the eyes in a straight position. Now, remember the superiors are intorters. So, if the right eye extorts, it means the inferiors in that eye (LIO and LIR) work and if the left eye intorts it means the superiors of that eye (RSO and RSR) work. When this happens, in the left eye the LSO and LSR should work. Now, the LSO is paralyzed and so cannot work. This will make the LSR only work in that eye and as a balance will not be maintained between these two muscles the left eye will move up as the LSR is also an elevator. Thus, one can diagnose the case of LSO. If we ask the patient to tilt the head to the right, the left eye will extort and the right eye will intort. In the right eye the intorters will be the RSR and RSO. Now the RSR is paralyzed and so the RSO will only work and the right eye will move downwards. Similarly, we can differentiate between the LIR and the RIO in the III step. If we tilt the head to the left, the right eye will extort and the muscles that will work are the RIO and RIR. As the RIO is paralyzed the RIR will only work and the right eye will move downwards. If we tilt the head to the right, the left eye will extort and the muscles that will work are the LIR and LIO. If the LIR is paralyzed the LIO will work and the left eye will move up. MANAGEMENT Occlusion When double vision is restricted to downward gaze as in fourth nerve paralysis, one can occlude the lower third of the spectacle lens before
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Table 9.1: Surgical treatment of superior oblique muscle paralysis (from von Noorden et al)
Class of SO Paralysis
Surgical treatment
Class 1 Class 2
Inferior oblique myectomy Superior oblique tuck (8-12 mm); recession of contralateral inferior rectus as a secondary procedure Hypertropia of < 25 prism diopters; inferior oblique myectomy. If there is hypertropia of < 25 prism diopters; inferior oblique myectomy with superior oblique tuck As in class 3 plus recession of ipsilateral superior rectus or contralateral inferior rectus Superior oblique tuck with recession of ipsilateral superior rectus or recession of contralateral inferior rectus As in classes 1-5 but bilateral surgery Explore trochlea
Class 3
Class 4 Class 5
Class 6 Class 7
the paretic eye with semiopaque scotch tape. This can be performed if the medical condition is not suitable for surgery. Surgery Depending on the class of SO paralysis the surgical treatment is done according to von Noorden (Table 9.1). REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Abducent Nerve and its Lesions Athiya Agarwal
INTRODUCTION The abducent nerve (sixth cranial nerve) is a small, entirely motor nerve that supplies the lateral rectus of the eyeball.1,2 NUCLEUS The abducent nucleus is situated in the lower part of the pons, close to the midline (Fig. 10.1). The facial nerve lies close to it and crosses it and turns around the nucleus to emerge from the brain just adjacent to the abducent nerve. Medial to the abducent nerve nucleus lies the medial longitudinal fasciculus and the pontine paramedian reticular formation (PPRF). Lateral to it lies the fifth cranial nerve and the sympathetic neuron. Just ventral to it lies the pyramidal tract. EXIT FROM THE BRAIN The abducent nerve exits from the brain between the pons and the medulla oblongata at the level of the pyramid. Next to it lies the facial nerve and then comes the eighth cranial nerve. COURSE The abducent nerve runs from the pons towards the middle cranial fossa (Fig. 10.2). Just beyond its origin the III, IV and V nerve are above it (Fig. 10.3). The sixth nerve passes inferior to the inferior petrosal sinus in an anterolateral direction and runs almost vertically up the back of the petrous temporal near its apex. It is placed and held here in a groove, which has a very variable appearance. Having arrived at the sharp upper border of the bone, it bends forwards practically at a right angle (Fig. 10.2) under the petrosphenoid ligament
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Fig. 10.1: Nucleus of the abducent nerve and the brainstem syndromes
Fig. 10.2: Course of abducent nerve
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Fig. 10.3: Abducent nerve and its relations
called the Gruber’s ligament to enter the cavernous sinus. It is thus passing through a canal called the Dorello’s canal. Cavernous Sinus In the cavernous sinus, the sixth nerve runs almost horizontally forwards. In the posterior part of the sinus, the nerve winds around the lateral aspect of the ascending portion of the internal carotid artery thus making a second bend this time however with a lateral convexity (Fig. 10.2). Further forwards the sixth nerve lies below and lateral to the horizontal portion of the internal carotid artery. Superior Orbital Fissure The sixth nerve then passes through the superior orbital fissure to enter the orbit. The nerve passes through the middle portion of the superior orbital fissure. Orbit In the orbit, the abducent nerve runs forwards and enters the ocular surface of the lateral rectus muscle (Fig. 10.4) just behind its middle portion before dividing into 3 to 4 branches.
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Fig. 10.4: Abducent nerve and other nerves in the orbit III A – Upper division of oculomotor; III B – Lower division of oculomotor; IV – Trochlear nerve; VI – Abducent nerve; LPS – Levator palpebrae superiors; SR – Superior rectus; LR – Lateral rectus; IR – Inferior rectus; MR – Medial rectus; SO – Superior oblique; IO – Inferior oblique
CLINICAL FEATURES OF SIXTH NERVE PALSY Deviation In the primary position the eyeball is converged due to the unopposed action of the medial rectus muscle. Ocular Movements Abduction is limited due to weakness of the lateral rectus muscle. Diplopia Uncrossed horizontal diplopia occurs, which becomes worse towards the action of the paralyzed muscle. Head Posture The face is turned towards the action of the paralyzed muscle to minimize diplopia.
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LESIONS Various lesions of the abducent nerve in its course (Fig. 10.5) can produce various syndromes. They are as follows: The Brainstem Syndrome A brainstem lesion of the sixth nerve may also affect the fifth, seventh and eight cranial nerves and also the cerebellum. The sixth nerve nucleus has also connections via the medial longitudinal fasciculus with the III nerve nucleus and so a lesion here produces a gaze palsy. Three syndromes can occur in the brainstem (Fig. 10.1). They are as follows. Millard-Gubler Syndrome In this the lesion is ventral and involves the facial nerve and the pyramidal tract. Thus, there is a sixth nerve paresis, ipsilateral VII nerve paresis and contralateral hemiparesis. Raymond’s Syndrome In this syndrome the lesion involves only the sixth cranial nerve and the pyramidal tract. Thus, the patient has a sixth nerve paresis and contralateral hemiparesis.
Fig. 10.5: Lesions of the abducent nerve
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Foville’s Syndrome In this the lesion is dorsally. As the lesion is dorsal the areas affected are the medial longitudinal fasciculus, the pontine paramedian reticular formation, the fifth nerve and the sympathetic neurons. Thus, the patient has horizontal conjugate gaze palsy, ipsilateral V, VI, VII and VIII nerve palsies with ipsilateral Horner’s syndrome. Subarachnoid Space Syndrome Elevated intracranial pressure may result in downward displacement of the brainstem, with stretching of the sixth nerve, which is tethered at its exit from the pons and in Dorello’s canal. This gives rise to nonlocalizing sixth nerve palsies of raised intracranial pressure. Thirty percent of patients with pseudotumor cerebri have sixth nerve paresis, besides papilledema and its visual field changes. Petrous Apex Syndrome The sixth nerve passes under the Gruber’s ligament in the Dorello’s canal. This makes it liable to a lesion. Gradenigo’s Syndrome This is due to a localized inflammation or extradural abscess of the petrous apex following complicated otitis media. This leads to: • Sixth nerve palsy • Ipsilateral decreased hearing (eighth nerve involvement) • Ipsilateral facial pain in the distribution of the fifth nerve • Ipsilateral facial paralysis. Pseudo-Gradenigo’s Syndrome This is seen in two conditions: Nasopharyngeal carcinoma This may cause serous otitis media due to obstruction of the eustachian tube and the carcinoma may subsequently invade the cavernous sinus causing sixth nerve paresis. Cerebellopontine angle tumor This may cause sixth nerve paresis with decreased hearing (VIII nerve), VII nerve palsy, V nerve palsy, ataxia and papilledema. Cavernous Sinus Syndrome In this other nerves in the cavernous sinus also are involved like the third, fourth and fifth nerves.
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Orbital Syndrome In this proptosis is an early sign and the optic nerve may appear normal or demonstrate atrophy or edema. The ophthalmic division of the fifth nerve is involved. The third, fourth and sixth nerves are also involved. It occurs due to trauma, tumors or inflammations. Isolated Sixth Nerve Palsy This can also occur. DIFFERENTIAL DIAGNOSIS • • • • • •
Thyroid eye disease Myasthenia gravis Duane’s syndrome type 1 Spasm of the near reflex Medial wall orbital blow-out fracture with restrictive myopathy Break in fusion of a congenital esophoria.
MANAGEMENT Occlusion One can perform occlusion when double vision is present in lateral gaze in patients with mild sixth nerve paresis. Treatment of the Cause One should find out the cause and treat it. Surgery A maximal recession-resection procedure suffices in most instances of incomplete abducens paralysis to restore a useful field of single binocular vision and to eliminate the head turn. If there is a complete paralysis of the lateral rectus muscle, one can perform a transposition of the superior and inferior rectus muscles to the insertion of the lateral rectus muscle. This is called Hummelsheim’s operation (Fig. 10.6). In this half the SR and LR are transposed to the area of the LR. Recession of the MR is also done. In Jensen’s operation also (Fig. 10.7), the transposition is done with recession of the medial rectus. In this operation, the LR is split and so also the SR and IR. Then the split portions of the SR and IR are sutured to the split portions of the LR.
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Fig. 10.6: Hummelsheim’s operation. 1. Half the SR and IR are transposed to the area of the LRl; 2.Recession of the MR is also done
Fig. 10.7: Jensen’s operation. 1. LR is split and so also the SR and IR are split. Then the split portions of the SR and IR are sutured to the split portions of the LR; 2. Recession of the MR is also done
Botulinum Toxin Injection Temporary paralysis of an extraocular muscle can be used in conjunction with the transposition procedures or in isolation. To determine the state of recovery of the lateral rectus following a sixth nerve palsy, a tiny dose of Botulinum toxin is injected into the belly of the overacting medial rectus muscle. This makes the medial rectus paralyzed and so the horizontal forces on the globe are more balanced and the esotropia reduced or eliminated. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Trigeminal Nerve Athiya Agarwal
INTRODUCTION The trigeminal nerve1,2 is the fifth cranial nerve and is both motor and sensory. On the sensory root there is a large ganglion called the trigeminal ganglion. NUCLEUS There are two portions to discuss regarding the nuclei: The first is the motor nucleus and the second is the sensory nucleus. The motor nucleus is in the upper pons. The sensory nucleus extends in continuity throughout the whole length of the brainstem and descends into the upper 2 or 3 segments of the spinal cord. The mesencephalic part is for propioception, the pontine part is for nice sensations, and the spinal or medullary nucleus is for nasty sensations. EXIT FROM THE BRAIN The trigeminal nerve exits from the brain at the level of the pons. Lateral to the fifth nerve is the middle cerebellar peduncle. The motor nerve emerges separately, slightly cranial and medial to its companion. TRIGEMINAL CAVE Together they pass below the tentorium cerebelli to the mouth of the trigeminal cave. This is a tubular prolongation of arachnoid. The sensory root expands into a large flat crescentic trigeminal ganglion. The motor root remains separate. The trigeminal ganglion lies in the trigeminal or Meckel’s cave. The anterior half of the ganglion gives off its three sensory divisions: (i) the ophthalmic division (V1), (ii) maxillary division (V2), and (iii) mandibular vision (V3). The motor
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root of the nerve has no connection with the ganglion but lies on its deep surface, crossing from the medial to the lateral side, to join the mandibular divisions of the trigeminal nerve (Fig. 11.1). The ophthalmic and maxillary divisions pass forwards in the lateral wall of the cavernous sinus . They are wholly sensory. The mandibular division passes straight down from the lower part of the ganglion to the foramen ovale. Here the motor root (Fig. 11.1) joins it. OPHTHALMIC DIVISION In the cavernous sinus, the ophthalmic division picks up sympathetic fibers from the cavernous plexus. These are for the dilator pupillae muscle. It divides just posterior to the superior orbital fissure into three branches, which pass through the superior orbital fissure to enter the orbit (Fig. 11.1).
Fig. 11.1: Ophthalmic division of the trigeminal nerve 1. Lacrimal nerve; 2. Frontal nerve: (A) Supraorbital N (B) Supratrochlear N; 3. Nasociliary nerve (A) Sensory root to the ciliary ganglion; (B) Long diliary nerve; (C) Posterior ethmoidal nerve; (D) Anterior ethmoidal nerve; (E) Infratrochlear nerve
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Lacrimal Nerve This is the smallest branch. It passes through the lateral portion of the superior orbital fissure lateral to the frontal and IV nerve and above the superior ophthalmic vein. In the orbit, it runs forwards just lateral to the upper border of the LR to reach the lacrimal gland. It also supplies the conjunctiva and skin of the lateral part of the upper lid. Frontal Nerve This is the largest of the three branches of the ophthalmic division. It arises in the cavernous sinus just behind the superior orbital fissure through which it enters the orbit. In the superior orbital fissure, it is between the lacrimal nerve and the IV cranial nerve. It runs above the LPS and divides into two branches—a large supraorbital and a small supratrochlear nerve. Nasociliary Nerve It is intermediate in size between the lacrimal and frontal nerve. It passes through the superior orbital fissure within the annulus tendon between the divisions of the third cranial nerve. In the orbit, it inclines medially with the ophthalmic artery above the optic nerve and below the SR. Thus, the nasociliary nerve, ophthalmic artery and the superior ophthalmic vein lie between the optic nerve and the SR muscle. The branches of the nasociliary nerve are: Sensory root of the ciliary ganglion This is given off just in front of the superior orbital fissure. It reaches the ciliary ganglion and does not synapse there. From the ciliary ganglion about 6 short ciliary nerves are given off which are sensory to the whole eyeball including the cornea but not the conjunctiva which is supplied by the lacrimal and supratrochlear nerves. Long ciliary nerves They are two in number and come off the nasociliary nerve. They pierce the sclera and pass in the suprachoroidal space to supply the iris, ciliary muscle and cornea. They also carry sympathetic fibers to the dilator pupillae muscle. Posterior ethmoidal nerve This passes through the posterior ethmoidal foramen. Anterior ethmoidal nerve This passes through the anterior ethmoidal foramen. This nerve enters the anterior cranial fossa and reaches the tip of the nose as the external nasal nerve. This is important as if a patient has herpes zoster and the tip of the nose is affected it means the nasociliary nerve is involved and that means the eye will definitely get involved. This is called Hutchinson’s rule.
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Infratrochlear nerve This is the terminal branch of the nasociliary nerve. MAXILLARY DIVISION The maxillary division passes through the foramen rotundum and gives off three posterior superior alveolar nerves (Fig. 11.2), a middle superior alveolar nerve and an anterior superior alveolar nerve. Then, it passes through the infraorbital canal and emerges as the infraorbital nerve. A loop of nerve called the loop of Woodron connects the posterior and middle superior alveolar nerves. It also gives off a nerve to supply the lacrimal gland, which travels along the lacrimal nerve. It also gives off the zygomatotemporal and zygomatofacial nerves. MANDIBULAR DIVISION The mandibular division passes through the foramen ovale and gives off first the meningeal branch, which passes back into the skull through the foramen spinosum. It then divides into two divisions—the anterior and posterior division. Each in turn has some branches (Fig. 11.3). Thus, the branches of the mandibular division are: • Meningeal branch • Anterior division which in turn has: 1. Temporal branch 2. Masseteric branch
Fig. 11.2: Maxillary division of the trigeminal nerve
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Fig. 11.3: Mandibular division of the trigeminal nerve 1. Meningeal branch; 2. Anterior division ; 3. Posterior division
3. Pterygoid branch 4. Buccal nerve. • Posterior division which in turn has: 1. Auriculotemporal nerve 2. Nerve to medial pterygoid 3. Lingual nerve 4. Inferior alveolar nerve. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Facial Nerve and its Lesions Athiya Agarwal
INTRODUCTION The facial nerve1,2 is the seventh cranial nerve and it is both a motor as well as a sensory nerve. NUCLEUS The seventh cranial nerve has three nuclei: The Main Motor Nucleus This lies in the lower part of the pons. The part of the nucleus that supplies the muscles of the upper part of the face receives corticonuclear fibers from both cerebral hemispheres. The part of the nucleus that supplies the muscles of the lower part of the face receives corticonuclear fibers from the opposite cerebral hemisphere only. Parasympathetic Nuclei These include the superior salivatory and lacrimatory nuclei. The former supplies the submandibular and sublingual glands and the latter the lacrimal gland. Sensory Nucleus This is situated in the upper part of the medulla oblongata. COURSE The facial nerve exits from the brain (Fig. 7.3) at the level of the junction between the pons and the medulla. Medial to it lies the VIth nerve and lateral to it lies the VIIIth nerve. The nerve then passes through the internal auditory meatus (Fig. 12.1). At its exit from the brain a
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cerebellopontine angle tumor can affect it. In such a case the nerves affected are the Vth, VIth, VIIth and VIIIth. The geniculate ganglion is located on the first bend of the facial nerve. This is a sensory ganglion. A nerve starts from the geniculate ganglion called the greater superficial petrosal nerve. This joins another nerve called the deep petrosal nerve, which is a branch from the sympathetic plexus around the internal carotid artery. These two nerves join to become the Vidian nerve or the nerve of the pterygoid canal. This then passes through the Vidian canal or the Pterygoid canal and ends in the pterygopalatine ganglion. This ganglion is the largest parasympathetic peripheral ganglion. It serves as a relay station for secretomotor fibers to the lacrimal gland and to the mucous glands of the nose, palate and pharynx. From the pterygopalatine ganglion secretomotor fibers go to the lacrimal gland. These hitchhike on to V2 (maxillary division of the trigeminal nerve) and then onto the lacrimal nerve (branch of
Fig. 12.1: Course of the facial nerve
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V1—ophthalmic division of the trigeminal nerve). Remember that the lacrimal gland’s tear production is due to the VIIth nerve and not due to the Vth nerve. From the geniculate ganglion the facial nerve curves downwards and gives off a nerve called the nerve to the stapedius. If this is cut the patient develops tinnitus. Then another nerve is given off called the chorda tympani nerve. This supplies taste for the anterior twothird of the tongue. The IXth (Glossopharyngeal nerve) nerve supplies the posterior one-third of the tongue. The VIIth nerve also supplies submandibular and sublingual glands. The facial nerve then comes out through the stylomastoid foramen and gives of the posterior auricular nerve. It then goes to supply the muscles of the face by dividing into two branches—zygomatotemporal and cervicofacial. The former gives off the temporal and the zygomatic branches. The latter gives off the cervical and mandibular branches. The buccal nerve is between these two branches. Thus, these five nerves supply the muscles of the face and this distribution is like a claw of a tiger and hence is called pes anserinus. The zygomatic branch supplies the orbicularis oculi muscle. LESIONS OF THE FACIAL NERVE The lesions of the facial nerve are shown in Figure 12.2. They are as follows: Supranuclear Lesion If the lesion is supranuclear the lower half of the face is only involved and if it is a lower motor neuron lesion the whole half of the face is involved. This is because the upper half of the face has a bilateral innervation. Cerebellopontine Angle Tumor Just as the VIIth nerve comes out from the brain it can get affected by the cerebellopontine angle tumor. The patient has: • Total ipsilateral facial weakness (VIIth nerve involvement) • Decreased tearing (lacrimation involved) • Hyperacusis (nerve to stapedius involved) • Decreased taste from the anterior two-third of the tongue (chorda tympani nerve involved) • Vth, VIth and VIIIth nerve involved with cerebellar dysfunctions.
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Fig. 12.2: Lesions of the facial 1. Supranuclear lesion; 2. Cerebellopontine angle tumor; 3. Geniculate ganglionitis (Ramsay Hunt syndrome); 4. Isolate ipsilateral tear deficiency; 5. Lesion before nerve to stapedius; 6. Lesion after nerve to stapedius; 7. Lesion after chorda tympani nerve; 8. Bell’s palsy – isolated total ipsilateral facial palsy; 9. Isolated partial ipsilateral facial palsy
Geniculate Ganglionitis Geniculate ganglionitis is known as the Ramsay-Hunt syndrome. The features are: • Same findings as in cerebellopontine angle tumors except no associated neurological deficits • May see zoster vesicles on tympanic membrane, external auditory canal or external ear.
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Isolated Ipsilateral Tear Deficiency Isolated ipsilateral tear deficiency occurs in nasopharyngeal carcinomas, which affect the Vidian nerve or the pterygopalatine ganglion. Lesion before Nerve to Stapedius Lacrimation is normal. The other findings are: • Hyperacusis (nerve to stapedius involved) • Decreased taste from the anterior two-third of the tongue (chorda tympani nerve involved) • Total ipsilateral facial weakness (VIIth nerve involvement). Lesion after Nerve to Stapedius • Decreased taste from the anterior two-third of the tongue (chorda tympani nerve involved) • Total ipsilateral facial weakness (VIIth nerve involvement). Lesion after Chorda Tympani Nerve Only total ipsilateral facial weakness (VIIth nerve involvement). Bell’s Palsy Only total ipsilateral facial weakness (VIIth nerve involvement). Isolated Partial Ipsilateral Facial Palsy In this only certain branches of the VIIth nerve are affected. SUMMARY Thus, if we understand the course of the facial nerve, we can diagnose the level of lesion in the facial nerve. REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003. 2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.
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Congenital Optic Nerve Anomalies
Priya Narang, Sameer Narang, Amar Agarwal
INTRODUCTION Congenital optic nerve anomalies are quite a common entity and are often included in the differential diagnosis of various clinical disorders as they are often associated with visual field defects central nervous system (CNS) malformations and other ocular abnormalities. A thorough knowledge of the embryological development of the optic nerve entails a better understanding of the development of optic nerve anomalies. The optic nerve develops from the optic stalk or optic pedicle. The closure of the fetal fissure converts the optic stalk into a rounded cord-like structure. Its cavity communicates on one side with the cavity of diencephalon and on the other side with the primary optic vesicle. The nerve fibers then grow from the ganglion cells towards the brain through the stalk. The optic nerve is then filled with glial tissue and fibrous septa. The sheaths of the optic nerve develop from the mesoderm. The medullation of the nerve fibers which begins from the brain and extends up to the lamina cribrosa is nearly complete at term. As stated above, any deviation from the normal development leads to congenital anomalies which are described here. CAUSES • • • • • • •
Abnormal small optic disk Aplasia Abnormal shape of the optic disk Bergmister’s papillae Optic nerve head drusen (Fig. 13.1) Myelineated nerve fibers (Fig. 13.2) Optic disk coloboma
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• Optic disk pit • Morning glory syndrome • Tilted disk. APLASIA Aplasia is a rare anomaly characterized clinically by a total blind eye with an afferent pupillary defect, an absent optic disk and an absent retinal vasculature. HYPOPLASIA The optic disk hypoplasia is a sporadic condition. The affected can be micro-ophthalmic or of normal size and usually exhibit a wide range of visual impairment from normal vision to severe visual loss with strabismus or nystagmus in bilateral cases. Visual acuity is determined primarily by the integrity of the papillomacular bundle. The visual fields show a localized defect. The disk is surrounded by a peripapillary halo, bordered by a dark pigment ring called as the double ring sign. Retinal vascular tortuosity is commonly seen. Histologically optic nerve hypoplasia is characterized by a subnormal number of optic nerve axons with normal mesodermal elements and glial supporting tissue. Some of the optic nerve hypoplasia are segmental. A pathognomonic superior segmental hypoplasia with an inferior visual field defect occurs in some children of insulin dependent diabetic mothers. In cases of homonymous hemianopic hypoplasia, there is congenital cerebral hemiatrophy. Patients with periventricular leukomalacia often have a unique form of optic nerve hypoplasia characterized by an abnormally large cup and a thin neuroretinal rim contained within a normal sized disk can be associated with intracranial and facial anomalies like septo-optic dysplasial De Morsiers syndrome, congenital hypopitutarism, hydrancephaly, arrhinencephaly, aniridia, homonymous optic hypoplasia associated with congenital hemispheric aplasia, cyclopia, enchelomeningocele and hypertelorism. De Morsier’s syndrome refers to the constellation of small anterior visual pathways, absence of septum pellucidum, and agenesis or thinning of the corpus callosum. MRI is the optimal noninvasive neuroimaging modality for delineating congenital CNS malformations in patients with septo optic dysplasia. In bilateral optic nerve hypoplasia the coronal MRI shows diffuse thinning of the optic chiasma.
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The detection of hypopitutarism is an essential component of the evaluation of children with optic nerve hypoplasia, because children with endocrinological deficiency are at risk for impaired growth, hypoglycemia, developmental delay, seizures and death. Parents should be asked about the history of protracted neonatal jaundice and previous episodes of hypoglycemia in the neonatal period. Infants with optic nerve hypoplasia have superimposed delayed visual maturation. Therefore infants who initially appear to be blind may have improvement of their vision during the first several months of life. Treatment Superimposed ambylopia should be treated with a trial of occlusion therapy children with hypopitutarism should be treated with pituitary hormone replacement. BERGMISTER’S PAPILLAE The glial sheath of Bergmister envelops the posterior third of the hyaloid artery it begins to atrophy about the seventh month of gestation, even before the main vessel atrophies. The extent of the atrophy is below the surface of the disk. If the atrophy at the disk is less complete a tuft of glial tissue may be seen thorough out the life over the optic disk called the Bergmister’s papillae. MYELINEATED NERVE FIBERS Medullation or myelineation of the optic nerve begins in the fetal life from the lateral geniculate body towards the globe. Normally the myelination is completed shortly after birth at which time the myelin sheath reaches the posterior aspect of the lamina cribrosa. The medullated fibers may be seen starting from the disk and extending towards the periphery (Fig. 13.2). Fundus examination shows irregular feather-like patches which may or may not obscure the retinal blood vessels. Rarely, isolated peripheral patches of myelination may also occur. Myelination of the nerve fibers results in visual field defects. Myopia, coloboma, polycoria, keratoconus, oxycephaly and neurofibromatosis have been associated with myelineated nerve fibers. OPTIC NERVE HEAD DRUSEN Deposition of hyaline like calcified material within the substance of the optic nerve head.Optic nerve head drusen (Fig. 13.1) can be
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inherited or can be associated with heredodegenerative conditions like retinitis pigmentosa or angioid streaks or can be following long standing papilledema, papillitis, vascular occlusions. Clinically has an irregular, nodular, mulberry like appearance of the surface of the disk. The physiological cup can be absent but venous pulsation is present there can be abnormal tortous, anomalously branching vessels. Disk can be pallor sometimes but will have irregular margins. They vary greatly in size, shape and number, smaller ones often coalesce to form larger ones. The differential diagnosis of optic disk drusen includes papilledema with which it is often confused. Fluorescein angiography helps to differentiate between both the conditions which closely simulate each other. Drusens’ exhibit the phenomenon of autofluorescence and may stain during the late stages of angiogram. They exhibit no leakage of fluorescein from the optic nerve head which is usually present in papilledema. Patients with disk drusen usually remain asymptomatic although few cases have been reported to develop peripapillary and macular hemorrhage. Drusens may directly compress the nerve fibers within the disk and cause various visual field defects like enlargement of the blind spot, arcuate scotoma or peripheral field constriction. Central visual acuity is usually good. COLOBOMA OF OPTIC DISK A coloboma of the optic disk (Fig. 13.1) results from incomplete closure of the embryonic fissure. The fissure initially closes in the middle and then extends anteriorly and posteriorly until a small crescent at the posterior pole remains open. When the lips of the fissure fail to fuse, typical colobomas result. The coloboma of the optic nerve may occur alone or may be associated with coloboma of the iris, retina, choroid or ciliary body. It usually occurs in two forms. Optic Disk Coloboma in Association with Retinochoroidal Coloboma This form of coloboma is more common and frequently occurs bilaterally. It is characterized by a large excavation which is usually situated inferiorly with the normal appearing disk tissue pushed superiorly. It is associated with superior visual field defects. The retinochoroidal coloboma may involve the optic nerve completely or occasionally there is a patch of healthy tissue between
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Fig. 13.1: Optic nerve head drusen
the retinochoroidal coloboma and the optic disk coloboma. Such colobomas are known as Bridge colobomas. Coloboma of the Optic Nerve Entrance These are isolated colobomas of the optic nerve wherein the disk shows an enlarged and excavated nerve head with an expanded scleral canal. It is usually unilateral and is associated with high myopia and amblyopia. The central area of the nerve shows persistent hyaloid remnants. The blood vessels which are believed to be cilioretinal in origin emerge like the spokes of a wheel in a radical fashion from the rim of the excavation. This is known as Morning glory syndrome (Fig. 13.2).
Fig. 13.2: Myelineated nerve fibers
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Occasionally mild failure of closure of embryonic fissure leads to the development of inferior crescent which is situated at the lower edge of the disk. It closely resembles the myopic crescent and is found to occur more commonly in hypermetropic and astigmatic eyes. MORNING GLORY SYNDROME The morning glory anomaly is a congenital, funnel shaped excavation of the posterior fundus that incorporates the optic disk. The disk is markedly enlarged, orange or pink in color and typically situated within a funnel shaped excavation. Surrounding the excavation is a variably elevated annular zone of altered retinal pigmentation. A white tuft of glial tissue overlies the recessed central portion of the lesion. The blood vessels appear increased in number and arise from the periphery of the disk. They run an abnormally straight course over the peripapillary retina and tend to branch at acute angles. It is often difficult to distinguish arterioles from venules. The macula may be incorporated into the excavation called as macular capture. Computed tomography shows a funnel shaped enlargement of the distal optic nerve at its junction with the globe. Visual acuity anges from 20/200 and finger counting. Morning glory syndrome is more common in females and rare in blacks. Serous retinal detachment is the most noted complication of this anomaly 26 to 38 percent of the eyes with morning glory result in retinal detachment. Associated with basal encephalocele with midfacial anomalies (hypertelorism, cleft lip, cleft palate, depressed nasal bridge, midline upper lid notch). MRI is indicated in patients with mid facial anomalies and neurological deficits because these patients are at high risk for an associated basal encephalocele. Treatment superimposed ambylopia should be treated with a trial of occlusion therapy. Patients with basal encephalocele should be evaluated for surgical repair. TILTED DISK Tilted disk is caused by an oblique insertion of the optic nerve into the globe. The upper temporal portion of the disk often lies anterior to the lower margin. The vertical axis of the disk is directed obliquely
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which gives it an oval appearance. This condition may be associated with visual field defects which involve the upper temporal quadrant because of the ectasia of inferonasal portion of the fundus. The visual fields in the congenital tilted disk does not respect the vertical meridian and it usually crosses the vertical meridian. Can be associated with the situs inversus of the blood vessels. Tilted disk is often found to be associated with degenerative high myopia wherein scleral ectasia or staphyloma involve the posterior pole temporal to the disk. This results in an oblique exit of the optic nerve. OPTIC DISK PIT Optic disk pit is usually seen as a small excavation along the temporal border of the disk covering nearly one-third of the surface of the disk. It is usually round or oval in shape and appears darker than the surrounding disk tissue probably because of the inability to illuminate these small deep excavations. It is usually unilateral and the disk may appear larger as compared to the fellow eye. In 15 percent of the cases it can be bilateral. A cilioretinal artery is found in 59 percent of the eyes with optic disk pit. Approximately 45 percent of the eyes with congenital optic disk pit develop serous macular elevations. The macula demonstrates the following progression of events.An inner layer retinoschisis cavity initially forms in direct communication with the optic pit an outer layer macular hole develops beneath the boundaries of the retinoschisis cavity. An outer layer retinal detachment develops around the macular hole. This outer layer detachment ophthalmoscopically can be mistaken for an pigment epithelial detachment, but it does not hyperflouresce on FFA. The outer layer detachment eventually enlarges and obliterates the retinoschisis cavity. At this stage, it becomes clinically indistinguishable from a primary serous macular detachment. BIBLIOGRAPHY 1. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005. 2. David J Apple, Maurice F. RABB (3rd ed) Ocular Pathology Mosby. 3. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003.
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Optic Nerve Tumors Nick Mamalis, Garrett Smith
INTRODUCTION Tumors of the optic nerve are relatively rare lesions. However, these lesions have significant risk for visual morbidity as well as other problems related to the central nervous system (CNS). Optic nerve glioma (astrocytoma) is the most common intrinsic tumor of the optic nerve. Juvenile pilocytic astrocytomas are by far the most common optic nerve tumor of children. Malignant gliomas of the optic nerve occur much less frequently and are seen in adults. Meningiomas of the optic nerve sheath are the second largest group of tumors which may affect the optic nerve and occur more commonly in adults. Lastly, secondary tumors of the optic nerve may arise from direct invasion from intraocular malignancies, meninges, adjacent structures, as well as distant metastases. OPTIC NERVE GLIOMAS Gliomas (juvenile pilocytic astrocytoma) are the most important optic nerve tumor of children, accounting for 65 percent of all intrinsic optic nerve tumors. 1 Gliomas are benign neoplasms arising from the neuroglia (astrocytes and oligodendrocytes). The majority of optic nerve gliomas are of astrocytic origin. However, a few rare optic nerve gliomas arise from oligodendrocytes. The descriptive term juvenile pilocytic astrocytoma is often used to describe this low-grade glioma. Gliomas grow slowly, but can spread under the dura to invade local structures. Patients typically present before the age of 20 with progressive visual loss, proptosis, and disk pallor with or without papilledema. Management includes observation, radiation, and surgery.
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Clinical Features Age In 1816 Antonio Scarpa first described optic nerve tumors and noted that the majority of his patients with gliomas were children. This fact has been substantiated in subsequent reports.1 In Dutton’s review of gliomas of the anterior visual pathway, the mean age of presentation was 8.8 years, with 70 percent of optic nerve gliomas occurring in the first decade of life, 20 percent in the second decade, and 10 percent between the ages of 20 and 80.1 Optic nerve gliomas are rare lesions estimated at 5 percent of intracranial tumors and 3 percent of all orbital tumors.2,3 Sex Optic nerve gliomas show equal to a slight female preponderance. One study of 594 patients had 295 (50 percent) females and 299 (50 percent) males.1 For gliomas confined to the optic nerve, earlier studies suggest a slight female preponderance of about 2:1.4,5 Location The size, growth pattern, and symptoms of the tumor depend upon the location of the tumor. In a study of 1278 cases, 75 percent involved the chiasm and optic nerve, while 25 percent were confined to the optic nerve alone.1 Of the lesions involving the chiasm, 7 percent were confined solely to the chiasm. Extension from the optic nerve into intraocular structures, meninges, and brain occurs in a few rare cases.6,7 It is thus helpful to divide optic nerve gliomas into two categories: orbital gliomas and intracranial or chiasmal gliomas. Orbital gliomas vary in size and growth pattern, but are generally slow growing benign tumors. Many orbital tumors slowly enlarge to reach a plateau, then remain unchanged for many years. This stabilization phenomenon is the reason that many considered these as hamartomas. Hamartomas are a focal malformation resembling a neoplasm, but is the result of faulty organ development composed of an abnormal mixture of tissue elements. Chiasmal gliomas seem to be more aggressive than orbital gliomas, and a few cases have reported malignant change.8,9 Of the tumors in the chiasm, 46 percent involved the hypothalamus or third ventricle, interfering with hypothalamic and pituitary function.1 Thus, patients with chiasmal tumors often present with endocrine abnormalities.
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Chiasmal tumors are also a concern because they can obstruct the third ventricle causing intracranial pressure elevation. Presenting Signs and Symptoms Orbital gliomas present with more orbital manifestations, while chiasmal gliomas demonstrate more neurological symptoms. However, both tumors share many of the same symptoms and many patients present with tumors involving both the orbital optic nerve and the chiasm. Regardless of tumor location, patients may experience some degree of unilateral visual dysfunction, visual field loss, afferent pupillary defect, decreased ocular motility, optic atrophy, pain, headache, and nystagmus. In Dutton’s review, 88 percent of patients presented with vision loss, 26 percent presented with acuities between 20/20 and 20/ 40, 19 percent between 20/50 and 20/200, and 55 percent were 20/ 300 or worse.1 Visual field loss occurred in 63 percent of patients and an afferent pupillary defect was seen in 75 percent of individuals. Visual loss occurs due to astrocyte proliferation within the confines of the dura and bone in cases of intracranial lesions. Initially, this causes longitudinal axon bundle separation and nerve fiber compression. The compression inhibits axoplasmic transport, with little loss of axonal conduction. Further compression leads to demyelination and mechanical disruption of axons. Intracranial gliomas are more confined and compress the axon faster, producing quicker vision loss. Orbital gliomas have more room to grow causing the characteristic slow progressive visual loss, because only individual axons degenerate. Spontaneous improvements in vision have been reported.10,11 This is theorized from variations in mucoid substance and hydration, and their effects on the optic nerve. In some cases rapid vision loss occurs due to occlusion of the vascular supply. Gliomas affecting the optic disk and retrolaminar portions of the nerve may compress the central retinal vein producing optic disk swelling. The visual loss is rapid and the clinical picture may simulate optic neuritis. Proptosis is often the chief complaint of an orbital glioma in young children, occurring 94 percent of the time in orbital lesions (Fig. 14.1).1 Because the tumor arises from the nerve within the muscle cone, the proptosis is usually axial. Minimal proptosis is 2.0 to 4.0 mm ranging up to severe proptosis at 10.0 mm or more. Nystagmus is another initial sign of both orbital and chiasmal gliomas occurring in 23 percent of patients.1 It may be vertical, horizontal, seesaw, or rotary. Pain or headaches, and limited ocular motility are other common symptoms of both types of gliomas.
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Fig. 14.1: Child with an optic nerve glioma of the left eye demonstrating proptosis with moderate inferior displacement of the left globe
On fundoscopic examination, 59 percent of patients demonstrated some degree of optic atrophy and disk pallor (Fig. 14.2). Disk swelling presents more frequently in orbital gliomas with a 48 percent occurrence rate.1 In chiasmal tumors, disk swelling occurred 22 percent of the time, and was often bilateral, due to increased intracranial pressure. Optociliary shunt vessels are occasionally seen with optic nerve gliomas, however they are far more common in optic sheath meningiomas. Other late and infrequent orbital glioma signs are venous stasis retinopathy with iris neovascular glaucoma, anterior segment ischemia, and hemorrhagic glaucoma from retinal vascular occlusion. In chiasmal gliomas, 27 percent of patients had third ventricle involvement causing increased intracranial pressure and 26 percent reported hypothalamic or endocrine abnormalities.1,12 The endocrine abnormalities included obesity, diabetes insipidus, panhypopituitarism, dwarfism and precocious puberty. Association with Neurofibromatosis Several studies have published a 15 to 21 percent occurrence rate of optic gliomas in neurofibromatosis patients. A study of 2186 published cases of patients with optic gliomas demonstrated 29 percent of them to have neurofibromatosis.1 Patients presenting to doctors with café-
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Fig. 14.2: Fundus examination of the same child showing diffuse atrophy of the optic nerve
au-lait spots and diagnosed with neurofibromatosis, should have regular ophthalmic examinations. Neurofibromatosis type 1 (NF-1) patients commonly develop multiple CNS astrocytomas and these lesions show a predilection for the orbital optic nerve and chiasm.13 NF-1 lesions tend to be multifocal and more extensive along the optic pathways than in patients without NF-1. Patients with bilateral optic gliomas usually have NF-1. 14 However, the incidence of visual symptoms and progressive neurologic deficits was lower among those patients with NF-1. Radiographic Findings On plain orbital radiographs 65 percent of optic gliomas can be visualized mainly through enlargement of the optic canal.1 The classic radiographic findings are enlargement of the optic foramen and Jshaped excavation of the sella turcica. The optic canals are usually symmetrical, and a 1.0 mm difference in the diameters or a vertical height of 6.5 mm or more is considered pathologic. Computerized tomography scans are more accurate, especially for orbital lesions. The tumor usually appears as a well-defined spindle or rounded shaped enlargement of the optic nerve.15 Kinking of the nerve is a characteristic finding in orbital gliomas, due to elongation of the nerve from secondary axial growth and downward deflection.15,16
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In evaluating anterior pathway lesions CT and Magnetic Resonance Imaging are equivalent.17 However, for chiasmal, hypothalamic, and optic tract lesions MRI is superior to CT, because in CT scans the tumor images are isodense to brain tissue.17,18 MRI differentiates tumor tissue from normal brain and neural structures better, thereby allowing improved diagnosing and monitoring. However, microscopic extension of the tumor cannot be detected. MRI has several other advantages over CT. MRI does not expose young children to ionizing radiation, allowing repeat serial examinations and it avoids scatter artifact near bone.19 On T2-weighted images, gliomas are hyperintense compared to normal optic nerve. Therefore, T2 weighted images is the best for demarcation of tumor borders (Fig. 14.3).20 Arachnoidal gliomatosis in neurofibromatosis patients can be visualized on T2-weighted axial MRI studies as an area of high-signal intensity (due to a high water content in the myxomatous tissue) surrounding a linear core of lower signal intensity. 16,21 Gliomas in T1-weighted images are slightly hypointense compared to normal optic nerve (Fig.14.4). T1-weighted image is best for demonstrating tissue composition, characterizing necrosis and mucinous degeneration.20 Histopathology Gross Appearance Optic nerve gliomas are typically contained within the dura (Figs 14.5A and B). The dura is stretched and thin, but usually intact. Typical gliomas appear tan to dusky red from the vascular congestion within the tumor. Orbital gliomas are characteristically fusiform, with the
Fig. 14.3: Axial MRI scan of a patient demonstrating a diffuse, fusiform enlargement of the optic nerve within the nerve sheath
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Fig. 14.4: Sagittal MRI scan demonstrating sausage-like enlargement of the optic nerve secondary to a glioma
Fig. 14.5A: Gross specimen demonstrating a relatively normal optic nerve on the left with disuse enlargement of the nerve itself within the intact sheath secondary to glioma
Fig. 14.5B: Low-power photomicrograph of the same patient demonstrating a normal optic nerve to the left with an intact sheath around it. There is an enlargement of the nerve itself secondary to the glioma with multiple large cystic spaces with myxomatous type degeneration (hematoxylin-eosin × 10)
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borders of the tumor difficult to delineate. Thus, it is helpful to obtain cross-sections at the end of each specimen.22 Gliomas may also invade the arachnoid and pia, and extend through the subdural space. This pattern occurs more often in neurofibromatosis patients.23 The nerve itself may be of normal thickness, but the overall diameter may be increased because of the perineural component. Cross-sections through the middle portion show the whitish nerve enlarged and surrounded by a cuff of arachnoidal tissue, which is then covered by stretched dura. Microscopic Findings Most optic nerve gliomas consist of elongated, spindle-shaped, pilocytic (hair-like) astrocytes (Fig. 14.6). Some researchers thus use the term juvenile pilocytic astrocytoma to differentiate them from other intracranial astrocytomas in older patients.24 These astrocytes have a benign histological appearance rarely demonstrating mitotic figures or malignant degeneration.22 The nuclei are usually uniform and oval with some being hyperchromatic (Fig.14.7). The cytoplasm is extended and contains glial filaments visible with special stains such as GFAP.25 These spindle-shaped astrocytes are fairly cohesive and damage the optic nerve by forming intersecting bundles that cause axon separation or compression of the nerve. The most distinctive and frequently encountered degenerative change found in optic nerve gliomas is the Rosenthal fiber.22 Rosenthal fibers are elliptical eosinophilic swellings found within astrocyte cell processes and surrounded by hyalinized connective tissue (Fig.14.8). These fibers consist of electron-dense granular material and glial
Fig. 14.6: Low-power photomicrograph of a juvenile pilocytic astrocytoma (hematoxylin-eosin × 100)
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Fig. 14.7: Moderate power photomicrograph demonstrating a low-grade astrocytoma of the optic nerve (hematoxylin-eosin × 200)
Fig. 14.8: Moderate power photomicrograph demonstrating multiple eosinophilic staining cytoplasmic inclusions consistent with Rosenthal fibers (hematoxylineosin × 250)
filaments. Foci of calcification from axonal debris commonly appear in the fiber. Vascular proliferation and atypia are frequently seen. These vessels are located either in the pial septa or between bundles of astrocytes. Periodically, enlarged congested sinusoidal vessels are encountered, but hemorrhagic necrosis rarely occurs. Pale staining areas that appear microcystic on hematoxylin-eosin staining are frequently interspersed among the astrocytes. With special stains, the microcystic spaces can show mucosubstance (myxomatous
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glioma) from mucin-producing cells that are present in the area. The “microcysts” are not intracellular but are extracellular accumulations of a mucicarmine-negative mucoid substance that stains with periodic acid-Schiff (PAS) and acid mucopolysaccharide. It is believed that astrocytes produce this mucoid hydrophilic material that also contributes to tumor enlargement.22 Older gliomas become fibrotic with lipoidal histiocytes and thickwalled fibrotic blood vessels suggestive of an angiomatous lesion, thus, making older gliomas more difficult to recognize. Optic nerve gliomas have two distinct growth patterns: perineural and intraneural. 26 In the perineural pattern, more of the perimeter astrocytes proliferate to widen the epipial-subarachnoid space within the intact dura while thus compressing the residual optic nerve as a central band. This circumferential tumor tissue consists mostly of proliferating astrocyte nests, intermingled with meningothelial cells, fibroblasts, and fibrovascular arachnoidal trabeculae, with mucinous and microcystic degeneration. Studies by Stern et al demonstrated these findings and they proposed the term arachnoidal gliomatosis (Fig.14.9). 26 Perineural growth often involves more of the optic pathways, because the perimeter astrocytes proliferate and can tunnel along the nerve under the dura. This perineural growth is associated with neurofibromatosis type 1 patients.16,26 One study observed 94 percent of glioma patients with perineural growth also had neurofibromatosis.16 The intraneural growth pattern predominates in patients without neurofibromatosis.26 In this pattern, the optic nerve enlarges instead of being compressed. Intra-axial astrocytes proliferate causing
Fig. 14.9: Low-power photomicrograph demonstrating proliferation of the lowgrade astrocytoma from the optic nerve to the area underlying the sheath demonstrating arachnoid gliomatosis from a patient with neurofibromatosis (hematoxylin-eosin × 50)
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expansion of fibrovascular trabeculae with slight cystic degeneration. The increasing nerve diameter crushes the subarachnoid space and fuses the pia mater to the arachnoid and dura.1 In both types of growth patterns the optic tumor enlarges by proliferation of neoplastic glial cells, accumulation of extracellular PASpositive mucosubstance secreted by the astrocytes, reactive gliosis, meningeal hyperplasia, and congestion within dilated blood vessels. Growth is usually slow, but accelerated expansion can result from cystic degeneration or intralesional hemorrhage. The majority of gliomas are benign and enlarge by bulk local growth causing demyelination and compression of optic nerve fibers. However, gliomas are true neoplasms and can tunnel under the dura extending along optic tracts and infiltrate the leptomeninges or intraocular structures.9,27 A few rare gliomas can undergo malignant evolution and spread throughout the cerebrospinal fluid.28,29 Gliomas and meningiomas of the optic nerve usually produce similar symptoms. Therefore, identifying which type of lesion the patient has is important. Current imaging and ultrasound techniques have become excellent at distinguishing the type of lesion the patient has, but when there is doubt many clinicians still advocate biopsy. However, even on biopsy confusion may arise. Possible reactive proliferation of meninges overlying the glioma making possible the misdiagnosis of meningioma if a very superficial biopsy of the optic nerve is done. Management Defining clear-cut guidelines for correct management of optic gliomas is difficult, because the natural course of gliomas is variable. Reported statistics and treatments results vary considerably causing much controversy to exist over the proper management of optic gliomas. A study by Wright and McDonald30 showed that in half of their patients, the tumor appeared to stop growing without treatment. It is thought that in this group the tumor was stable upon presentation or slowly enlarged to reach a plateau remaining unchanged for many years. In the other half of the patients, the glioma continued growing, resulting in clinical signs and symptoms that required surgical removal. This study shows the dilemma of whether to surgically intervene causing blindness in that eye or to just follow the tumor radiographically and maintain partial vision. If the tumor appears stable it is worth watching, but if the tumor progresses intracranially, it can be deadly.
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If a patient presents with an optic glioma that appears to be fairly asymptomatic and confined to the orbit, current thought is to follow the patient without treatment.1 Because many studies have shown approximately half the gliomas plateau and remain dormant, with some cases of vision actually improving later on.30,31 Serial CT or MRI scans, pupillary reactions, visual acuity, and visual field examinations should be done to monitor tumor growth. If the tumor enlarges to cause blindness, severe proptosis, or pain, then complete removal by lateral orbitotomy is warranted.32 The risk of just monitoring gliomas is that some can spread throughout the CSF invading distant areas. A few rare gliomas undergo malignant evolution.8 Kocks reported a child who developed lumbar spinal metastases from a chiasmal glioma.33 However, the majority of gliomas grow slowly over months to years and spread by local enlargement. If on radiographic scans, the tumor shows extension along the intracranial portion of the nerve and threatens the chiasm, then surgery is also recommended. Once the tumor extends to the optic chiasm the risk of death rises to about 28 percent.1 Surgical intervention at this point does not improve survival, and has significant visual morbidity and potential mortality. Some research suggests a short-term benefit from radiotherapy in doses exceeding 4500 cGy for chiasmal and midbrain tumors,11,34 but overall survival and ultimate recurrence show no benefit to radiotherapy.1,35 This raises the question as to whether radiotherapy is worth the side effects, because radiation in children has many permanent adverse effects on the CNS and endocrine function. 36 Among 511 patients treated with radiotherapy and followed for 10 years, 69 percent demonstrated stable vision, 42 percent showed tumor progression, and 28 percent died from the disease. In contrast to the treated group, 203 similar patients were followed without treatment and showed comparable results; 77 percent demonstrated stable vision, 42 percent showed tumor progression, and 29 percent died.1 In a study by Packer et al they advocated that chemotherapy could significantly delay the need for radiation in children.14 Yet, there is little published data on the role of chemotherapy. Although optic gliomas are benign neoplasms they can result in significant morbidity and mortality. Therefore, the clinical approach to these tumors must be vigilant, with attentive observation and aggressive intervention when necessary.
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MALIGNANT GLIOMAS OF THE OPTIC NERVE Malignant astrocytomas of the optic nerve are a rare, but aggressive and deadly disease. The tumor arises from malignant astrocytes located in intracranial optic pathways and rapidly spreads to invade numerous structures. Patients typically are middle-aged adults that present with decreased vision, visual field loss, retro-orbital pain, and disk swelling. Most patients progress to blindness and death within a year.37 Clinical Features In contrast to benign gliomas that occur in children, malignant gliomas are a disease of middle-age. In Dutton’s review the average of presentation was 47, with patients ranging from six to eighty. 1 Malignant optic gliomas show a male preponderance, with 65 percent occurring in males, and 35 percent occurring in females. Malignant gliomas of the optic nerve arise from malignant astrocytes that originate in intracranial optic pathways.37 Rarely, it arises in the orbital optic nerve. Malignant gliomas rapidly spread anterior and posterior to involve the optic nerve, chiasm, optic tracts, hypothalamus, third ventricle, thalamus, temporal and occipital lobes. The clinical course is unilateral visual loss that progresses to blindness and death in an average of 11 weeks, but can range up to 60 weeks.1 The malignant astrocytes typically attack one side, then rapidly spread through the chiasm to involve both optic nerves. At presentation 64 percent of patients have bilateral visual loss. The final visual acuity reported in a study of 22 patients showed that in the less affected eye only 23 percent had vision of 20/400 or better, while 63 percent were NLP. In the more affected eye 86 percent were NLP. Visual field defects occurred in 94 percent of patients.1 On initial presentation normal optic disks are often seen, but within weeks the disk progressively swells. If the patient lives long enough optic atrophy ensues. Malignant gliomas typically arise intracranially or in the chiasm and generally affect intracranial optic pathways. Thus, neurological symptoms are more common than proptosis. Neurological signs include convergence and gaze abnormalities, paresthesias, partial ophthalmoplegia, seizures, confusion, and hallucinations. Hypothalamic involvement usually occurs in the final stages and causes many of the deaths.37
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Retro-orbital pain is a common symptom. The visual loss and retroorbital pain often lead to an initial diagnosis of optic neuritis. Rapid and progressive visual loss should include radiological imaging. Radiology Plain orbital radiographs rarely reveal malignant gliomas. Computerized tomography provides a 79 percent chance of disclosing the tumor on initial examination.1 Images portray an enlarged chiasm and optic nerves. Few reported cases have used MRI, but MRI has revealed the tumor in all cases.38,39 Pathology Histological examination is consistent with malignant astrocytoma showing atypical pleomorphic astrocytes with numerous mitotic figures. Secondary vascular and endothelial proliferation can also be found.40 The malignant cells encircle and compress the optic nerve inhibiting axoplasmic transport and capillary perfusion, causing demyelination and axonal degeneration. The neoplastic cells usually extend under the pia along the optic pathways or directly within the brain substance. The tumor can spread to invade the orbit, hypothalamus, third ventricle, basal ganglia, or intraparenchymal brain. Prognosis Malignant gliomas are a sad and devastating disease with the overall mortality rate of 97 to 100 percent with a mean survival of 8.7 months following diagnosis.1 Some patients treated with 5000 to 6000 cGY radiotherapy showed temporary visual acuity improvements and slightly prolonged life, but ultimately died from the disease. Advances in cancer research will hopefully led to better treatments. OPTIC NERVE MENINGIOMAS Meningiomas are the second most common optic nerve tumor, after gliomas. 41 Meningiomas are benign neoplasms arising from meningothelial cells typically in the arachnoid. Patients generally are middle-aged adults and present with decreased vision, visual field loss, proptosis, disk atrophy, disk swelling, and later on optociliary shunt vessels. Meningiomas grow slowly, but are invasive and infiltrate surrounding structures. Management includes conservative monitoring, radiotherapy, and surgery.
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Clinical Features In contrast to gliomas, meningiomas occur later in life. In Dutton’s review of optic nerve meningiomas, a study of 256 patients demonstrated the average age of presentation to be 40.8 years.41 The average age for males was 36, and the average age for females was 42. Even though the average age for females was older, meningiomas show a slight female preponderance at 61 percent female and 39 percent male. Approximately 4 to 10 percent of meningiomas occur in children and tends to be more aggressive.22,41 Therefore, meningiomas should still be included in the differential diagnosis of a lesion causing proptosis and progressive visual loss in a child. Similar to gliomas, there is a proven higher incidence of meningiomas in patients with neurofibromatosis.42 Researchers classify optic nerve meningiomas into three types based on tumor origin. Primary tumors if they originate from the meninges in the optic nerve and secondary tumors if they originate from cranial meninges and then extend into the orbit. Approximately 90 percent of meningiomas affecting the optic nerve are secondary, extending from the olfactory groove and sphenoid ridge.43,44 A third rare type, ectopic (extradural) arise from congenitally displaced meningothelial cells along the floor or roof of the orbit. Signs and Symptoms The signs and symptoms of meningiomas depend upon the origin and location of tumor growth. For ease of understanding, meningiomas affecting the eye can be divided into four groups depending upon location: (i) dura restricted, (ii) orbital, (iii) intracanalicular, and (iv) secondary. The natural course of meningiomas is unpredictable, because they can invade any surrounding structure. Therefore, different tumors share many of the same clinical and pathologic signs. Ninety-five percent of primary meningiomas have unilateral involvement, but 5 percent are bilateral.41 The bilateral meningiomas typically arise within the optic canal or chiasm (intracanalicular).41,43 The most common symptom of all meningiomas is gradual vision loss occurring over one to five years. A study of 380 patients demonstrated 96 percent to have decreased vision; with 45 percent presenting with acuities between 20/20 and 20/40, 31 percent between 20/60 and 20/400, and 24 percent with counting fingers or worse.41,45 The second most common symptom was visual field loss occurring in 83 percent of patients.41,46 Peripheral constriction was the most characteristic visual field loss. Central, centrocecal, paracentral
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scotomas, and increasing blind spot visual field losses also occurred. Decreased color vision was reported in 73 percent of the patients. Early or rapid vision loss occurs in dura-restricted meningiomas. These meningiomas grow similar to a glioma, and remain confined within the dura. As the meningothelial cells proliferate within the subdural spaces, the tumor begins compressing the optic nerve and inhibits axoplasmic transport. Further compression leads to demyelination and mechanical disruption of axons. Similarities to gliomas also occur when the meningioma infiltrates the nerve and widens the septa. More characteristic slow visual loss occurs when the meningioma penetrates the dura and grows outside of the dura (orbital meningiomas). In this situation, meningothelial cells proliferate for many months to years within the orbit and the tumor becomes very large before compressing the optic nerve. The tumor begins to slowly push on the posterior pole of the globe causing axial proptosis, hyperopia, and striae. Axial proptosis is often the presenting symptom of meningiomas and occurred in 59 percent of the study patients.41 In this situation, when the tumor enlarges outside the dura, it can impinge upon the extraocular muscles limiting ocular motility. Forty-seven percent of study patients complained of limitation of ocular motility. The tumor infrequently encroaches on one of the cranial nerves, causing cranial nerve palsy.44 In dura-restricted meningiomas, as the tumor enlarges it impinges and stiffens the optic nerve causing a mechanical restriction of extraocular muscle function. Disk swelling is an early finding in 48 percent of patients of all types.41 Disk swelling occurs due to compression of the central retinal vein and meningeal vasculature or spread of tumor cells to the anterior end of the perineural space, with interference of disk circulation. As compression of the optic nerve progresses the incidence and degree of optic atrophy increases. Forty-nine percent of patients progress to develop optic atrophy. The classic pathognomonic triad for meningiomas of gradual unilateral vision loss, optic atrophy, and optociliary shunts (Fig. 14.10) occurs in 30 percent of patients.41 Imes et al47 followed the development of optociliary shunts over eight and a half years in a woman with an optic nerve meningioma. The first two years the woman had chronic disk swelling and congestion of the central retinal vein. After two years, Imes observed the dilation of regressed, but vestigeal, retinociliary anastomoses that were present in earlier embryonic development. The prolonged inhibition of retinal vein circulation re-established the flow of blood from retinal veins through optociliary shunts into the choroidal circulation. Then as the optic atrophy worsened in the woman, the shunts regressed over the years.
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Fig. 14.10: Fundus photograph of the optic nerve from an elderly female patient demonstrating optociliary shunt vessels with atrophy of the nerve
Meningiomas affecting the optic canal or chiasm (intracanalicular) may simulate atypical retrobulbar neuritis with decreased visual acuity and optic atrophy. Proptosis and disk edema are rarely seen. Tumors in the sphenoid ridge may also affect the nerves to the extraocular muscles resulting in strabismus as a presenting sign. Radiology Plain orbital radiographs rarely see meningiomas. Cases of hyperostosis of neighboring bone will show up, but these are rare.48 Computerized tomography has revolutionized diagnosing optic nerve tumors, with visualization of 97 percent of meningiomas.41 CT scans should be obtained before and after iodinated contrast medium infusion. Thin sections (1.5 to 3 mm) should be taken to demarcate tumor edges. Dura-restricted meningiomas often appear as a welldefined smooth tubular enlargement of the optic nerve.48 The majority (64%) of meningiomas shows this diffuse tubular thickening of the optic nerve.49 Orbital tumors growing outside the dura show globular perioptic or irregular and serrated enlargement, unlike dura-restricted tumors that demonstrate a fusiform shape.48,49 The dura-restricted tumors are commonly confused with gliomas, because they both are ensheathed by the dura. Helpful findings are calcifications, which are usually present in meningiomas and not typically found in gliomas.50 Another important radiographic sign helpful in diagnosing meningiomas is tram tracking.41 In tram tracking the optic nerve can be seen as a central black line through the whitish mass (Fig. 14.11). Tram tracking, however, may also be visualized in inflammatory
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Fig. 14.11: CT scan of the eye and orbit showing a diffuse meningioma of the nerve anteriorly with the “tram-track” sign
perioptic pseudotumor and other diffuse sheath thickenings.51 In coronal views the denser and thickened optic nerve sheath appears as a dense circle around the more radiolucent optic nerve. Magnetic resonance imaging offers more precise and sensitive detection of intracanalicular or intracranial extension of meningiomas than CT.48,52 T1-weighted images should include fat-suppressed finecut axial and coronal images with and without gadolinium enhancement. The T1-weighted images disclose the characteristic tram-track appearance of the optic nerve in meningiomas. Axial and coronal T2weighted images provide the most sensitive method of determining the extent of tumor involvement. An additional imaging technique called OctreoScan is used to support and follow the diagnosis of meningiomas. OctreoScan (Indium-111 pentetreotide) is a radio-labeled ligand that binds to the somatostatin receptors in meningiomas. The binding is highly sensitive, but not very specific because other classes of tumors also bind somatostatin. OctreoScan is therefore helpful in following tumor progression in cases of observation or tumor treatment response.52 Histopathology Meningiomas can arise from any of the different cells that comprise the meninges (Fig. 14.12). However, current researchers believe the majority of meningiomas arise from the meningothelial cap cells found in arachnoid villi.41,42 Arachnoid villi are smaller and similar to arachnoid granulations (grape-like tufts of arachnoid that penetrate dural venous sinuses and affect transfer of CSF to the venous system). Arachnoid villi are collected along the intraorbital and canalicular
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Fig. 14.12: Gross photograph of an optic nerve sheath meningioma
portions of the optic nerve and also along the sphenoid ridge, tuberculum sellae, olfactory groove, and other areas of the meninges. Neoplastic meningothelial cap cells are spindle or oval shaped and form densely packed concentric whorls with psammoma bodies (Figs 14.13A and B). Psammoma bodies are calcifications that develop in the whorl centers from hyalinization and deposition of calcium salts (Figs 14.14A and B). This pattern is the meningothelial pattern and is the most idiosyncratic degenerative change found in meningiomas. Meningiomas rarely show mitotic figures or malignant degeneration.22 Cells from the arachnoidal trabeculae of the meninges are of mesodermal origin and can proliferate to cause fibroblastic meningiomas. This type may metastasize. 41 A combination of meningothelial and fibroblastic is called the transitional pattern. Meningiomas are benign neoplasms that grow slowly over months to years. Similar to gliomas, meningiomas can tunnel in the subdural spaces traveling along the optic pathways and infiltrate intraocular structures. However, unlike gliomas, meningiomas are invasive and can penetrate the dura to invade adjacent orbital structures, such as the extraocular muscles, sclera, or bone.22 Optic nerve meningiomas arising in the orbit can spread posteriorly through the optic canal to the chiasm or into the middle cranial fossa. At present, it is thought that meningiomas do not invade the brain or pituitary, and it appears meningiomas have little effect on the pituitary-hypothalamic axis or increasing ICP. 42,44,53 Meningiomas can infiltrate the bone by entering the haversian canals and initiate hyperostosis and bony proliferation.54
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Fig. 14.13A: Low-power photomicrograph demonstrating nests or whirls of meningothelial cells underlying the optic nerve sheath which is to the left (hematoxylin-eosin × 100)
Fig. 14.13B: Medium-power photomicrograph of a meningioma showing the spindle cells with a concentric whirl-type arrangement in the center (hematoxylin-eosin × 200)
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Fig. 14.14A: Medium-power photomicrograph of a meningioma demonstrating cells with a round nucleus and an eosinophilic staining cytoplasm with a small psammoma body in the center (hematoxylin-eosin × 200)
Fig. 14.14B: Higher power photomicrographs showing a large, calcified, hyalinized, psammoma body (hematoxylin-eosin × 250)
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Management The management of optic nerve meningiomas is controversial because their course is unpredictable. Traditional management includes observation, radiotherapy, and surgery. Traditionally, if a patient presents with the tumor confined to the orbit and visual acuity better than 20/40, observation was recommended.46 Observation includes ophthalmic examinations and CT or preferably MRI scans every six months. If visual acuity is progressively lost below 20/40, the visual field is constricting, or imaging scans show dangerous growth the patient is encouraged to undergo radiotherapy for preservation of vision.46,52 If the eye is totally blind and the meningioma confined to the orbit then the patient can choose to monitor the tumor or surgically excise it. If the meningioma is spreading posterior or enlarging and causing proptosis then total removal should be performed. Because of the characteristic slow growth and benign pattern of primary optic nerve meningiomas, the overall tumor-related mortality rate is 0 percent according to Dutton’s major review.41 This fact coupled with the risks of radiation or surgery are the reasons many researchers advocate observation in patients over 40. The disadvantages to sole observation is the possible risk of tumor spread. Of 228 orbital lesions only 20 percent showed posterior extension.41 However, tumors originating in the canal or chiasm have a 38 percent chance of contralateral involvement.52 The most obvious disadvantage of simple observation is gradual vision loss. Kennerdell et al showed that of 39 patients that did not receive treatment of any kind, not one maintained good visual acuity for more than four years.46 This is in striking contrast to patients treated with radiotherapy where 73 percent of them had improved vision.41 Radiotherapy is the most promising treatment modality because of its ability to inhibit tumor growth and restore vision.46,55 Older radiation treatments were less precise and exposed the chiasm, contralateral optic nerve, and surrounding tissues to ionizing radiation, causing optic neuropathy and secondary malignancies. Leber et al56 studied the dose to damage relationship of older modalities. They found that the patients receiving less than 10 Gy per day had no incidences of optic neuropathy. 26.7 percent of patients receiving 10 to 15 Gy developed sequelae and 77.8 percent of patients receiving greater than 15 Gy developed sequelae. The newer conformal radiotherapy is much more precise and attains an improved therapeutic ratio. The accuracy of computer-guided stereotactic radiotherapy only
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exposes the patient to 1.8 Gy.52 This explains why many current researchers advocate radiotherapy as primary management in all optic nerve meningiomas as well as adjuvant treatment for incompletely resected tumors.46,55,57,58 A few successful therapeutic surgical interventions have been reported in tumors confined to the anterior or middle third of the optic nerve.46,52,59-61 However, most surgical intervention results in blindness, typically attributed to ischemia of the optic nerve.46,52 In blind eyes surgical excision of the tumor is warranted if the tumor threatens, the optic canal, chiasm, or intraocular structures. Surgical removal is also indicated in blind eyes if the enlarging tumor causes pain or proptosis. Although optic nerve meningiomas are benign neoplasms, they can result in blindness. Many technological advances have helped patients maintain their vision, but the clinical approach must be attentive and when necessary aggressive treatment implemented. SECONDARY OPTIC NERVE TUMORS The majority of tumors involving the optic nerve are from secondary malignancies. Only 18 percent of tumors arise within the optic nerve itself, while 82 percent invade the nerve secondarily.62 There are four main routes of invasion into the optic nerve: direct extension from the eye, meninges, adjacent structures, and blood-borne metastatic invasion via the ophthalmic artery. Ginsberg et al63 presented a review of 117 cases of secondary optic nerve tumors. They found 39 percent to arise from intraocular tumors, 33 percent from blood-borne tumor seeding, 20 percent from meningeal tumors, and 8 percent invaded from adjacent structures. Extension from the Eye The most common secondary optic nerve malignancy is from intraocular structures. 62 Retinoblastoma and uveal melanoma constitute the majority of secondary intraocular tumors. Retinoblastoma has been known for many years to invade the optic nerve, with 26.7 percent of patients with retinoblastoma in a mass eye and ear study showing extension into the optic nerve.62 The tumor is usually limited by the lamina cribrosa, but may extend past it to invade the chiasm or brain.64 Predisposing factors to nerve invasion include elevated intraocular pressure, glaucoma, tumor seeding into the vitreous, and necrotic retinoblastoma.65 The prognosis significantly worsens once the tumor progresses beyond the lamina. Kopelman
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et al66 reported that the most dangerous risk factor of retinoblastoma was penetration of the coats of the eye, and the second most significant risk factor was the degree of optic nerve invasion. Uveal melanomas invade the nerve less than retinoblastoma, with 6.5 percent of uveal melanomas invading the optic nerve.62 The diffuse melanomas have a more malignant cell type than typical nodular melanomas. Thus, diffuse melanomas are more aggressive at invading the optic nerve and carry a worse prognosis. Juxtapapillary melanomas can invade the nerve by direct extension causing hyperemia and disk edema. The lamina cribrosa generally limits the tumor growth, but posterior extension into the orbit, chiasm,65 and brain67 have been reported. Weinhaus et al68 on univariate analysis found a direct correlation between tumor death and the degree of optic nerve invasion. Predisposing factors for invasion include elevated intraocular pressure, juxtapapillary location, glaucoma, and necrotic tumors. Blood-Borne Metastasis Hematopoietic malignancies involving the optic nerve include leukemia, lymphomas, and myeloma. In most forms of leukemia the optic nerve and nerve head become infiltrated with abnormal white blood cells. Children with acute lymphoblastic leukemia are the most affected with 13 percent of patients having optic nerve invasion.69 In 384 autopsy specimens, Kincaid et al70 found 82 percent of patients to have ocular involvement. Unilateral or bilateral visual loss is the most common clinical symptom. Disk swelling, as well as pallor, splinter hemorrhages from infiltration, and increased intracranial pressure often occur. Histologically, perivascular and discrete tumor infiltration can be seen. Combined intrathecal chemotherapy and localized radiotherapy have improved visual function in some cases.71 A few cases of Hodgkin’s and Non-Hodgkin’s lymphomas involving the optic nerve have been reported.62 Invasion into the optic nerve occurs from both chronic systemic lymphoma and CNS lymphoma that invades via the meninges. Multiple myeloma occasionally invades the eye, but only one case of optic nerve invasion has been reported.72 Solid tumors that metastasize to the eye and optic nerve are rare and typically occur in parallel with widespread systemic metastasis. In Ginsberg’s review of primary metastatic sites to the optic nerve, breast cancer was the most recurrent distant tumor at 33 percent. Lung cancer followed second at 11 percent and stomach third at 6 percent. Others included pancreas 3 percent, mediastinum 3 percent, skin 3 percent, melanoma 2 percent, uterine 2 percent, and ovarian at 2 percent.63
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Extension from the Meninges and Brain Neoplastic cells gain access to the optic nerve by anterior progression through the optic canal via the subarachnoid space. Neoplasms entering the nerve by this route include primary intracranial tumors (meningial carcinomas, reticuloendothelial sarcomas) plus secondary metastatic tumors to the CNS, which include lymphomas, melanoma, and myeloma.65 The course of these neoplasms is variable depending on the aggressiveness of the tumor. Slow growing tumors can spread anteriorly producing papilledema and visual dysfunction after the disease is advanced. Aggressive, rapidly proliferating neoplasms invade the axonal bundles, causing early visual loss and disk edema. The prognosis is poor once visual loss occurs from metastasis, with survival less than two years. 73 Palliative treatment consisting of chemotherapy and radiation has resulted in transient improvement in visual function in some cases.74 Primary tumors from the CNS (ependymoblastoma, pituitary adenoma) rarely invade the optic nerve, but will commonly compress the optic nerve causing a neuropathy.62 Extension from Adjacent Structures Tumors arising in the orbit, nasal sinuses, and nasopharynx generally compress the optic nerve instead of invading it. Visual field loss, proptosis, and pain are common presenting symptoms. Treatment for orbital tumors involves radiation, which often causes optic neuropathies. REFERENCES 1. Dutton JJ. Gliomas of the anterior visual pathway. Survey of Ophthalmol 1994;38:427-49. 2. Fowler FD, Matson DO. Gliomas of the optic pathways in childhood. J Neurosurg 1957;14:515-28. 3. Reese AB. Tumors of the Eye. Harper and Row: Hagerstown 1976;163-64. 4. Borit A, Richardson EP Jr. The biological and clinical behavior of pilocytic astrocytomas of the optic pathways. Brain 1982;105:161-87. 5. Desoretz DE, Blitzer PH, Wang CC. Management of glioma of the optic nerve and/or chiasm. Cancer 1980;45:1467-71. 6. Grimson BS, Perry DD. Enlargement of the optic disk in childhood optic nerve tumors. Am J Ophthalmol 1984;97:627-31. 7. Lloyd LA. Gliomas of the optic nerve and chiasm in childhood. Trans Am Ophthalmol Soc 1973;71:488-535. 8. Wilson WB, Feinsod M, Hoyt WF, et al. Malignant evolution of childhood chiasmal pilocytic astrocytoma. Neurology 1974;26:322-25.
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9. De keizer RJW, de Wolff-Rouendaal D, Bots GTA. Optic glioma with intraocular tumor seeding in a child with neurofibromatosis. Am J Ophthalmol 1989;108:717-25. 10. Frohman LP, Epstein F, Kupersmith MJ. Atypical visual prognosis with an optic nerve glioma. J Clin Neuro-ophthalmol 1985;5:90-94. 11. Hoyt WF, Baghdassarian SA. Optic gliomas of childhood—natural history and rational for conservative management. Br J Ophthalmol 1969;53:793-98. 12. Albert D, Puliafito C. Foundation of Ophthalmic Pathology. Appleton-CenturyCrofts: New York 1979. 13. Riccardi VM, Eichner JE. Neurofibromatosis: Phenotype, Natural History and Pathogenesis. Johns Hopkins University Press: Baltimore 97, 1986. 14. Packer RJ, Sutton LN, Bilaniuk LT. Treatment of chiasmal/hypothalamic gliomas of childhood with chemotherapy—an update. Ann Neurol 1988;23:79-85. 15. Jakobiec FA, Depot MJ, Kennerdell JS. Combined clinical and computed tomographic diagnosis of orbital glioma and meningioma. Ophthalmol 1984;91:137-55. 16. Imes RK, Hoyt WF. Magnetic resonance imaging signs of optic nerve gliomas in neurofibromatosis-1. Am J Ophthalmol 1991;111:729-34. 17. Brown EW, Riccardi VM, Mawad M, et al. MR imaging of optic pathways in patients with neurofibromatosis. Am J Neuroradiol 1987;8:1031-36. 18. Haik BG, Saint-Louis L, Bierly J, et al. Magnetic resonance imaging in the evaluation of optic nerve gliomas. Ophthalmol 1987;94:709-17. 19. Holman RE, Grimson BS, Drayer BP, et al. Magnetic resonance imaging of optic gliomas. Am J Ophthalmol 1985;100:596-601. 20. Patronas NJ, Dwyer AJ, Papathanasiou M, et al. Contributions of magnetic resonance imaging in the evaluation of optic gliomas. Surg Neurol 1987;28: 367-71. 21. Seiff SR, Brodsky MC, MacDonald G, et al. Orbital optic glioma in neurofibromatosis—magnetic resonance diagnosis of perineural arachnoidal gliomatosis. Arch Ophthalmol 1987;105:1689-92. 22. Spencer WH, Rao NA. Ophthalmic Pathology: An Atlas and Textbook (4th ed) WB Saunders: Philadelphia 1996;580-608. 23. Jenkin D, Angyalfi S, Becker L, et al. Optic glioma in children—surveillance, or irradiation? Int J Radiat Oncol Biol Phys 1993;25:215-25. 24. Yanoff M, Davis RL, Zimmerman LE. Juvenile pilocytic astrocytoma (glioma) of the optic nerve—clinicopathologic study of sixty-three cases. In Jakobiec FA (Ed): Ocular and Adnexal Tumors. Ala: Aesculapius:Birmingham, 1978;685-707. 25. Cutarelli PE, Rossmann UR. Immunohistochemical properties of human optic nerve glioma. Investigative Ophthalmol and Visual Sci 1991;32:2521-24. 26. Stern J, Jakobiec FA. The architecture of optic nerve gliomas with and without neurofibromatosis. Arch Ophthalmol 1980;98:505-11. 27. Dossetor FM, Landau K, Hoyt WF. Optic disk glioma in neurofibromatosis type 2. Am J Ophthalmol 1989;108:602-03. 28. Civitello LA, Packer RJ, Rorke L, et al. Leptomeningeal dissemination of low grade gliomas in childhood. Neurology 1988;38:562-66. 29. Bruggers CS, Freidman HS, Phillips PC, et al. Leptomeningeal dissemination of optic pathways gliomas in three children. Am J Ophthalmol 1991;111:719-23. 30. Wright JE, McDonald WI. Management of optic nerve gliomas. Br J Ophthalmol 1980;64:545-52.
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31. Glaser JS, Hoyt WF, Corbett J. Visual morbidity with chiasmal glioma—longterm studies of visual fields in untreated and irradiated cases. Arch Ophthalmol 1971;85:3-12. 32. Shields JA, Shields CL. Atlas of Orbital Tumors Lippincott William and Wilkins: Philadelphia 1999;91-102. 33. Kocks W, Kalff R, Reinhardt V, et al. Spinal metastasis of pilocytic astrocytoma of the chisama opticum. Child Nerv Syst 1982;5:118-20. 34. Chang CH, Woods EH. The value of radiation therapy for gliomas of the anterior visual pathway. In Brockhurst SA, Borouchoff BT, et al (Eds): Controversy in Ophthalmology WB Saunders: Philadelphia, 1977;876-86. 35. Alvord EC, Lofton S. Gliomas of the optic nerve or chiasm. J Neurosurg 1988;68:85-98. 36. Kingsley DPE, Kendall BE. CT of the adverse effects of therapeutic radiation of the central nervous system. Am J Neuroradiol 1981;2:453-60. 37. Hoyt WF, Meshel LG, Lessell S, et al. Malignant optic glioma of adulthood. Brain 1973;96:121-32. 38. Evens PA, Brihaye M, Buissert T, et al. Gliome malin du chiasma chez l’adulte. Bull Soc Belg Ophthalmol 1987;224:59-60. 39. Hufnagel TJ, Kim JH, Lesser R. Malignant glioma of the optic chiasm eight years after radiotherapy for prolactinoma. Arch Ophthalmol 1988;106:1701-05. 40. Hamilton AM, Garner A, Tripathi RC, et al. Malignant optic nerve glioma— report of a case with electron microscope study. Br J Ophthalmol 1973;57: 253-64. 41. Dutton JJ. Optic nerve sheath meningiomas. Surv Ophthalmol 1992;37:167-83. 42. Spencer WH. Primary neoplasms of the optic nerve and its sheaths—clinical features and current concepts of pathogenetic mechanisms. Trans Am Ophthalmol Soc 1972;70:490-528. 43. Craig WM, Gogela LJ. Intraorbital meningiomas—a clinicopathologic study. Am J Ophthalmol1949;32:1663-80. 44. Wilson WB. Meningiomas of the anterior visual system. Surv Ophthalmol 1981;26: 109-27. 45. Alper MG. Management of primary optic nerve meningiomas. J Clin Neuroophthalmol 1981;1:101-17. 46. Kennerdell JS, Maroon JC. The management of optic nerve sheath meningiomas. Am J Ophthalmol 1988;106:450-57. 47. Imes RK, Schatz H, Hoyt WF. Evolution of opto-ciliary veins in optic nerve sheath meningioma. Arch Ophthalmol 1985;103:59-60. 48. Mafee MF, Goodwin J, Dorodi S. Optic nerve sheath meningiomas, role of MR imaging. Radiologic Clin North Am 37: 37-58. 49. Sibony PA, Krauss HR. Optic nerve sheath meningiomas—clinical manifestations. Ophthalmol1984;91:1313-26. 50. Jakobiec FA, Depot MJ, Kennerdell JS. Combined clinical and computed tomographic diagnosis of orbital glioma and meningioma. Ophthalmol 1984;91:137-55. 51. Dutton JJ, Anderson RL. Idiopathic inflammatory perioptic neuritis simulating optic sheath meningioma. Am J Ophthalmol 1985;100:424-30. 52. Fineman MS, Augsburger JJ. A new approach to an old problem. Surv of Ophthalmol1999;43:519-24.
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53. Newell FW, Beamon TC. Ocular signs of meningiomas. Am J Ophthalmol 1958;45:30-40. 54. Als E. Intraorbital meningiomas encasing the optic nerve. Acta Ophthalmol 1969;47:900-03. 55. Kupersmith MJ, Warren FA, Newall J, et al. Irradiation of meningiomas of the intracranial anterior visual pathway. Ann Neurol 1987;21:131-37. 56. Leber KA, Borgloff J, Pendl G. Dose-response to tolerance of the visual pathways and cranial nerves of the cavernous sinus to stereo tactic radiosurgery. J Neurosurg 88: 43-50, 1998. 57. Smith JL, Vuksanovic MM, Yates BM. Radiation therapy for primary optic nerve meningiomas. J Clin Neuroophthalmol1981;1:85. 58. Barbo NM, Gutin PH, Wilson CB, et al. Radiation therapy in the treatment of partially resected meningiomas. Neurosurgery1987;20:525. 59. Cristant L. Surgical treatment of meningiomas of the orbit and optic canal—a retrospective study with particular attention to the visual outcome. Acta Neurochir 19984;126:27-32. 60. Delfini F, Missori P, Tarantino R, et al. Primary benign tumors of the orbital cavity—comparative data in a series of patients with optic nerve glioma, sheath meningioma or neurinoma. Surg neurol 1996;45:147-54. 61. Clark WC, Theofilos CS. Primary optic sheath meningiomas. J Neurosurg 1989;70:37-40. 62. Christmas NJ, Mead MD, Richardson EP, et al. Secondary optic nerve tumors. Surv Ophthalmol 1991;36:196-206. 63. Ginsberg J, Freemond AS, Calhoun JB. Optic nerve involvement in metastatic tumors. Ann Ophthalmol 1970:2:604-17. 64. Merriam GR. Retinoblastoma—analysis of seventeen autopsies. Arch Ophthalmol 1974;44:71-108. 65. Spencer WH. Optic nerve invasion of intraocular neoplasm. Am J Ophthalmol 1975;80:465-71. 66. Kopelman JE, Mclean IW, Rosenburg SH. Multivariate analysis of risk factors for metastasis in retinoblastoma treated by enucleation. Ophthalmol 1987;94: 371-77. 67. Jones DR, Scobie IN. Intracerebral metastases from ocular melanoma. Br J Ophthalmol 1988;72:246-47. 68. Weinhaus RS, Seddon JM, Albert DM, et al. Prognostic factor study of survival after enucleation for juxtapapillary melanoma. Arch Ophthalmol 1985;103:1673-77. 69. Allen RA, Straatsma BR. Ocular involvement in leukemia and allied disorders. Arch Ophthalmol 1961;66:490-508. 70. Kincaid MC, Green WR. Ocular and orbital involvement in leukemia. Surv Ophthalmol 1983;27:211-32. 71. Murray KM, Paolini F, Goldman JM, et al. Ocular involvement in leukemia— report of three cases. Lancet 1977;1:829-31. 72. Gudas PP Jr. Optic nerve myeloma. Am J Ophthalmol 1971;71:1085-89. 73. Miller NR. Secondary tumors of the central nervous system. In Miller NR (Eds): Walsh and Hoyt’s Clinical Neuro-Ophthalmology. Williams and Wilkins: Baltimore 1988;1662-709. 74. Altrocchi PA, Reinhardt PH, Ecman PB. Blindness and meningeal carcinomatosis. Arch Ophthalmol 1972;88:508-12.
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Abnormalities of Optic Nerve Head
Reena M Choudhry, Saurabh Choudhry, Amar Agarwal
OPTIC ATROPHY Optic atrophy is characterized by loss of conducting function of the optic nerve, with an increase in pallor of the disk as a result of gliosis and loss of capillaries of the disk.1-16 Optic atrophy results from injury to any portion of the retino-geniculate pathway (from retinal ganglion cells to lateral geniculate body). • Primary optic atrophy is caused by lesions which cause a death of the axons of the optic nerve without causing a swelling of the optic nerve. The lesions may affect the visual pathway from retrolaminar portion of the optic nerve to the lateral geniculate body. Causes of primary optic atrophy can be retrobulbar neuritis, compression due to aneurysms or tumors, toxic and nutritional neuropathies and trauma. • Secondary optic atrophy is caused by conditions, which produce swelling of the optic nerve head. The causes include papilledema, papillitis, and anterior ischemic optic neuropathy. • Consecutive optic atrophy is a result of retinal or choroidal disease leading to destruction of ganglion cells. It could occur following chorioretintis, Retinitis pigmentosa, pathological myopia, central retinal artery occlusion and after pan retinal photocoagulation. • Cavernous (Glaucomatous) optic atrophy is caused by loss of nerve fibers in advanced glaucoma. The neuroretinal rim is healthy in glaucomatous optic atrophy in contrast to primary optic atrophy with a large cup. • Segmental optic atrophy is usually seen in toxic and nutritional neuropathies and ischemic optic neuropathies. • Hereditary optic atrophy may be congenital or associated with Leber’s optic neuropathy, Kejr syndrome, Behr syndrome and other systemic syndromes like Friedreich’s ataxia.
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Fig. 15.1: Optic atrophy
Clinical Features • Primary optic atrophy shows chalky white disk (Fig. 15.1) with sharply defined margins and normal appearing retinal vessels and surrounding retina (Table 15.1). • Secondary optic atrophy shows dirty gray pallor of the optic nerve head with poorly defined margins, obliterated cup, sheathing and narrowing of arteries in the peripapillary area. • Consecutive optic atrophy shows waxy pallor of the disk with marked attenuation of the arteries. Signs of associated retinal pathology are present. • Cavernous optic atrophy shows a pale disk with pathological cupping, thinning of the neuroretinal rim, nerve fiber layer loss and laminar dot sign. • Segmental optic atrophy shows pallor of the temporal side or other segments with sharply defined margins and no retinal pathology. • Relative afferent pupillary defect is present in unilateral and asymmetric cases. • Color vision is reduced in correlation with the visual loss. • Visual fields show varied defects depending upon the cause of the optic atrophy. • Kejr syndrome: This is an hereditary optic atrophy which is bilateral and is autosomal dominant. It occurs between the ages of 4-10 years. • Behr syndrome: This is autosomal recessive and is another hereditary optic atrophy condition. Occurring during the first 10 years of life. • Wolfram syndrome: This is another hereditary optic atrophy disease and is also referred to as DIDMOAD = Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness.
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Table 15.1: Differences between primary, secondary and consecutive optic atrophy Features
Primary
Secondary
Consecutive
1. Disk color 2. Margins 3. Lamina cribrosa 4. Retinal vessels
Chalky white Well-defined Well-seen
Dirty grey Blurred Not seen
Waxy pallor Well-defined Well-seen
Normal
Marked attenuation of arteries
5. Surrounding retina
Normal
Peripapillary sheathing and narrowing of arteries. Veins are Tortous and Walls are Sclerosed Edema
6. Example
Pituitary Tumor, optic Nerve tumor
Papilledema, papillitis
Associated retinal pathology Retinitis pigmentosa, CRA occlusion
• Foster-Kennedy syndrome: There is unilateral papilledema and contralateral optic atrophy. It occurs due to frontal lobe tumors. • Pseudo Foster-Kennedy syndrome: In this there is optic atrophy in one eye and a disk swelling in the other eye due to AION. Differential Diagnosis One should differentiate between primary, secondary and consecutive optic atrophy (Table 15.1). Optic Neuritis Optic neuritis is defined as an inflammatory or demyelinating disorder of the optic nerve characterized by sudden loss or diminision of vision, associated with ocular pain and dyschromatopsia.1-16 Most common cause of optic neuritis is demyelinating disorders like multiple sclerosis. Viral (mumps, measles, herpes zoster, cytomegalovirus, or HIV), bacterial (tuberculosis, syphilis or lymes disease) and other (histoplasmosis,cryptococcosis,toxoplasmosis or toxocariasis) infections can also cause optic neuritis. In children optic neuritis can occur post-immunization. Other possible causes are adjacent paranasal sinus inflammation, systemic collagen vascular diseases and intra ocular inflammation.
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Clinical Features • Decreased visual acuity ranging from 6/9 to no perception of light. There is rapid worsening in next few days reaching maximum deficit by 1-2 weeks. Recovery occurs over next 4-6 weeks. • Decreased color vision, which is more than the visual deficit. Acquired optic nerve disease tends to cause red-green defects. An exception occurs in glaucoma and in autosomal dominant neuropathy which initially causes blue-yellow deficit. It has been recently found that visual field loss in glaucoma is detected earlier if perimetry is performed using a blue light stimulus on a yellow background. Acquired retinal disease tends to cause blue-yellow defects except in cone dystrophy and Stargardt’s disease which cause a predominantly red-green defect. • Contrast sensitivity and stereoacuity is reduced. • Relative afferent pupillary defect (RAPD) is present in unilateral or asymmetric cases. • Visual fields show central, centrocaecal or arcuate field defects. • Cells may be seen in the vitreous. • Fundus examination: Retrobulbar neuritis: Optic disk appears normal (most common presentation in adults). Papilitis: The disc appears swollen and hyperemic (Fig. 15.2A), associated with or without peripapillary flame shaped hemorrhages. Cells in the posterior vitreous may be present. Retina can show venous sheathing in the peripapillary area. Neuroretinitis: Disk edema associated with macular star (least common). On fluorescein angiography (Fig. 15.2B) there is pre-papillary capillary dilatation and leakage very similar to papilledema. There is hyperfluorescence of the disk with late leakage possibly involving the nerve fiber layer. With resolution of the swelling there is a pale disk with variable loss of the pre-papillary capillaries evidenced on fluorescein angiogram. There is ocular pain, which worsens on ocular movements. Age at presentation ranges between 20-45 years and women are more commonly affected than men. In children the involvement is bilateral. Some patients may complain of defective color vision. Patients with multiple sclerosis may have transient obscurations of vision on exertion or rise in body temperature (Uhthoff’s symptom).
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Figs 15.2A and B: Papillitis: (A) color picture (B) FFA
Management • In mild cases (vision 20/30 or better) only observation is indicated, as the disease is self-limiting. • In cases where vision is 20/40 or worse intravenous (IV) methylprednisolone 1 gm daily for 3 days followed by oral steroids 1 mg/kg body weight for 11 days is administered. Optic Neuritis Treatment Trial (ONTT) • Patients treated with intravenous methylprednisolone followed by oral steroids recovered vision faster than patients treated with oral steroids alone. • The final visual outcome at 1 year was same with or without IV steroids. • Patients treated with oral steroids alone had higher rate of recurrences and increased rate of second eye involvement.
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PAPILLEDEMA Papilledema (Fig. 15.3) is a passive, non-inflammatory, hydrostatic edema of the optic nerve head, secondary to raised intracranial pressure (ICP). 1-16 It is usually bilateral, although it may be asymmetrical. One should differentiate it from papillitis (Table 15.2). The following are the causes of raised ICP, which in turn cause papilledema. 1. Intracranial space occupying lesions. 2. Focal or diffuse cerebral edema. 3. Blockage of flow of cerebrospinal fluid (CSF) within the ventricular system (aqueduct stenosis). 4. Reduced absorption of CSF (meningitis, subarachnoid hemorrhage, etc). 5. Hypersecretion of CSF by choroid plexus tumor. 6. Increase in CSF viscosity (Guillain-Barre syndrome). 7. Benign intracranial hypertension (pseudotumor cerebri). Clinical Features Clinically, papilledema can be classified into four stages. 1. Early stage: In this stage the visual symptoms are absent and visual acuity remains normal. Ophthalmoscopically the optic nerve head shows hyperemia, blurring of disk margins. Mild disk swelling may be present which is best appreciated with slit lamp biomicroscopy. Absence of spontaneous venous pulsations could be an early sign of papilledema. Presence of spontaneous venous pulsations rules out papilledema.
Fig. 15.3: Papilledema
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Table 15.2: Differences between papillitis and papilledema
Features
Papillitis
Papilledema
1. 2. 3. 4. 5.
Unilateral Sudden Sudden Moderate Central or centrocaecal scotoma
Bilateral Insidious Gradual Marked Concentric Contraction of the visual field Clear
Laterality Onset Loss of vision Swelling of the disk Field defects
6. Posterior vitreous
Fine opacities
2. Established stage: In this stage patient may be asymptomatic or complain of transient visual obscuration lasting few seconds. During these episodes the vision may vary from mild blurring to complete blindness. Ophthalmoscopically there is gross elevation of optic nerve head with engorged veins. The disk margins are markedly blurred and edematous nerve fiber layer obscures the traversing blood vessels. Peripapillary splinter hemorrhages, cotton wool spots, choroidal folds and retinal striae (Paton’s lines) are present. The macula may have hard exudates forming an incomplete star. 3. Chronic stage: Constriction of peripheral fields may be associated with the enlargement of the blind spot. Ophthalmoscopically hemorrhages and disk edema slowly resolves. The cup ultimately obliterates and nerve fiber layer begins to atrophy giving gray white color to the disk. 4. Atrophic stage; Secondary optic atrophy ensues. The optic disk is pale to white with indistinct margins and attenuated and sheathed vessels in the peripapillary area. Severe atrophy of nerve fiber layer is present. Other signs are: • The pupillary reactions are normal. • The color vision is unaffected in early stages but as the chronic papilledema progresses to optic atrophy the color vision becomes abnormal. • Visual fields—In the initial stages enlargement of the blind spot is present but as the atrophy sets in constrictions of peripheral fields are seen. • Unilateral or bilateral sixth nerve palsy may be present due to stretching of the sixth nerve in the posterior fossa as a result of raised ICP.
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Very rarely papilledema may be unilateral or more pronounced in one eye than the other (preexisting unilateral optic atrophy, Foster Kennedy syndrome or unilateral congenital anomaly of optic nerve sheath) (Fig. 15.4). On the fluorescein angiogram there is immediate filling of the dilated capillaries giving hyperfluorescence and leakage from both the prepapillary and peripapillary capillary plexus and associated leakage into the surrounding retina. With resolution of the papilledema the optic disk is flat and pale and there is lack of filling of the pre-papillary capillary plexus. In long-standing cases, the prepapillary capillary plexus might anastomose with the choroidal plexus with a consequent optociliary shunt vessel. In chronic papilledema the optic disk becomes pale and there is only minimal leakage of fluorescein. Ocular symptoms mainly consist of bilateral transient obscurations of vision lasting few seconds. These are often precipitated by postural change. Rarely patients may complain of reduced vision. Double vision, which may be intermittent, can be present in some cases. Systemic symptoms are associated with raised ICP and consist of headaches, which are more severe early in the morning or in the recumbent position. Other symptoms like nausea, vomiting, loss of consciousness and motor rigidity may be present.
Fig. 15.4: Foster-Kennedy syndrome
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Management The treatment is focused towards the cause of raised ICP. If increased ICP is related to a mass lesion, removal of the mass is the obvious treatment of choice. Medical treatment in the form of carbonic anhydrase inhibitors may help reduce the ICP. If the lesion cannot be removed, or if the CSF absorption is reduced then treatment is directed towards shunting of the CSF into the peritoneal cavity (Lumboperitoneal shunts). In cases of idiopathic intracranial hypertension optic nerve sheath decompression has been advocated by some authors to alleviate fluid retention within the surrounding meninges by creating a small fenestration site within the intraorbital portion of the nerve. While this procedure has yielded some positive results, it is extremely complex work and may fail in up to one-third of all cases. ARTERITIC ANTERIOR ISCHEMIC OPTIC NEUROPATHY (AAION) Etiology AAION is infarction of the prelaminar or laminar portion of optic nerve head due to inadequate perfusion by posterior cilliary arteries and is most commonly associated with giant cell arteritis (GCA). GCA is the most common cause of AAION. Other conditions that may cause AAION are herpes zoster, rheumatoid arthritis, relapsing polychondritis, Takayasu’s arteritis, systemic lupus erythematosus, and periarteritis nodosa. Classic Signs • Unilateral visual loss (gross reduction of vision). • Relative afferent pupilliary defect (RAPD) is present in unilateral cases. • Fundus examination shows pale and swollen disk. Splinter hemorrhages at and around the disk margins may be present. Within 1-2 months the disk swelling subsides and optic atrophy ensues. • Visual fields commonly have altitudinal defect in eyes which can be tested. • In few cases cranial nerve palsy may be present as an associated sign. • Systemic signs of GCA are tender, palpable non-pulsatile temporal arteries.
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• Involvement of other arteries may lead to myocardial infarction, renal failure and brainstem stroke. In some cases central retinal artery occlusion may be an associated finding. • Erythrocyte sedimentation rate (ESR) and C-reactive protein are invariably raised. Symptoms Patients classically present with sudden onset unilateral visual loss (partial or complete), which may rapidly become bilateral. Average age of presentation is usually 55 years and above. Women are affected more commonly than men. Patients may give history of amaurosis fugax before the onset of visual loss. Diplopia may be present in few cases. Systemic complaints of headaches, jaw claudication, scalp tenderness, myalgia, fever and weight loss may be present. Differential Diagnosis 1. Non-arteritic anterior ischemic optic neuropathy - Patients are younger than those with GCA. - The visual loss is less severe. - Systemic hypertension or diabetes mellitus is frequently present. - Erythrocyte sedimentation rate (ESR) is usually normal. - Involvement of other eye is less common. - No benefit from systemic steroids. 2. Optic neuritis (papillitis) - Affects younger age group (20-40 years). - The visual loss is severe and recovery is better. - Pain during ocular movements is frequently present. - The disk swelling is hyperemic and associated with cells in posterior vitreous. 3. Compressive optic neuropathy - Visual loss is gradual in onset and slowly progressive. - Disk edema may be absent. - Proptosis or restricted ocular movements are often present (associated with orbital disease). - Systemic signs and symptoms of GCA are absent. Work-up 1. Temporal artery biopsy should be performed in patients where GCA is suspected before starting steroid therapy or within 2 weeks. (The biopsy specimen should be at least 2.5 cm long and if the
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biopsy is negative but response to steroids is positive biopsy of opposite artery should be considered). 2. Temporal artery Doppler can also be done. Risk Factors In AAION associated with GCA the involvement of other eye without treatment is seen in 50 percent of cases within days to few weeks. Management AAION is a medical emergency and needs to be treated with intra venous methyl prednisolone 1 gm daily for 3 days followed by 80100 mg oral corticosteroids on a slow tapering dose for a period of 6 months to 1 year to prevent involvement of the other eye. Patients of GCA confirmed by temporal artery biopsy are maintained on initial dose of corticosteroids for 4 weeks until ESR normalizes and slowly tapered while monitoring the ESR levels. Pharmacology Rare instances of anaphylactoid (e.g., bronchospasm) reactions have occurred in patients receiving parenteral corticosteroid therapy so appropriate precautionary measures should be taken prior to administration, especially when the patient has a history of allergy to any drug. There are also reports of cardiac arrhythmias and/or circulatory collapse and/or cardiac arrest following the rapid administration of large IV doses of methylprednisolone sodium succinate (greater than 0.5 gram administered over a period of less than 10 minutes). Bradycardia has been reported during or after the administration of large doses of methylprednisolone sodium succinate, and may be unrelated to the speed or duration of infusion. POSTERIOR ISCHEMIC OPTIC NEUROPATHY (PION) In the posterior variety (PION) there is no disk edema noted in the acute phase although the symptoms and clinical findings are otherwise similar to the anterior variety. The circulation impairment affects the posterior vessels and there is no impairment of the axoplasmic flow . The PION is seen more frequently in cases with acute severe blood loss or sustained hypotension, postsurgical complications, migraine, collagen vascular diseases and giant cell arteritis.
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REFERENCES 1. Hayreh SS. Risk factors in AION. Ophthalmology. 2001;108(10):1717-8. 2. Chan CC, Paine M, O’Day J. Steroid management in giant cell arteritis. Br J Ophthalmol. 2001;85(9):1061-4. 3. Ischemic Optic Neuropathy Decompression Trial: twenty four month update. Arch Ophtalmol. 2000;118(6):793-8. 4. Beri M et al. Anterior ischemic optic neuropathy. VII. Incidence of bilaterality and various influencing factors. Ophthalmology. 1997;94(8):1020-8. 5. Jacobs M, Taylor D. The systemic and genetic significance of congenital optic disc anomalies. Eye. 1991;5(Pt4):470-5. Review. 6. Villalonga Gornes PA, Galan Terraza A, Gil-Gibernau JJ. Ophthalmoscopic evolution of papilary colobomatous malformations. J Pediatr Ophthalmol Strabismus 1995;32(1):20-5. 7. Frisen L, Holmegaard L. Spectrum of optic nerve hypoplasia. Br J Ophthalmol. 1978; 62(10:7-15). 8. Traboulsi EI, O’Neill JF. The spectrum in the morphology of so called “morning gllory disc anomaly”. J Pediatr Ophthalmol Stabismus. 1998;25(2):93-8. 9. Lee MS, Gonzalez C. Unilateral peripapillary myelinated retinal nerve fibers associated with stabismus, amblyopia, and myopia. Am J Ophthalmol. 1998;125(4):554-6. 10. Principles and Practice of Ophthalmology by Albert Jackobiec, Chapter 20;Page: 2549-60. 11. Atlas of optic neuritis disorders by Thomas J Spur. 12. Focal points 1993, Module 5, Henry JL Van, DyK. 13. Walsh and Hoyt’s Clinical Neuro-opthalmology. 5th Edition. The Essentials. Neil R Miller, Nancy J Newman. 196-220. 14. Trobe JD, et al. The impact of optic neuritis treatment trial on the practices of ophthalmologists and neurologists. Ophthalmology. 1999;106(11):2047-53. 15. Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee; India; 2003. 16. Amar Agarwal. Handbook of Ophthalmology; Slack inc, USA, 2006.
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Ocular Myopathies S Soundari
INTRODUCTION Myasthenia results from the dysfunction of the neuromuscular junction caused by autoimmunity. Ocular myasthenia most commonly presents with diplopia, ptosis or both that is variable and characteristically worse towards the end of the day. Serum antibodies to acetylcholine receptors are detected in 90 percent of the patients with generalized myasthenia but only 50 percent will be detected in ocular myasthenia. Neonatal forms of myasthenia gravis occur in 10 to 15 percent of children born to the mothers with myasthenia gravis, because of the placental transfer of antibodies to ach receptor. The impairment of the neuromuscular conduction causes weakness and fatigue of the skeletal musculature, but not of cardiac and involuntary muscles. The disease affects females twice as commonly as males and may be ocular, bulbar or generalized. CLINICAL FEATURES • Myasthenic signs and symptoms are variable and tend to worse with fatigue and stress • Fatigability: When testing for lid fatigue, the patient is asked to look up without blinking at the examiners hand for 1-2 min. Lid fatigue on prolonged up gaze is perhaps the most frequently elicited signs • Peek sign: When the patient is asked to close the lids gently, one or both inadvertently open slightly or peek • There can absence of Bell’s phenomenon • Cogan’s lid twitch: After prolonged down gaze refixation to the primary position results in overshooting of the upperlid • Hop of the upper lid occurs on looking to the side
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• Myasthenic ptosis, when unilateral is associated with controlateral lid retraction • If one eye lid is elevated manually as the patient looks up, the fellow eyelid will show fine oscillatory movements • Ice pack test: The degree of ptosis improves after the ice pack is placed on the eyelid for 2 minutes. The test is negative in non myasthenic ptosis • Diplopia: This is very frequently vertical although any of the muscle can be involved. Pupil is not involved. A pseudointernuclear ophthalmoplegia can occur • Saccadic abnormalities like hypometric large saccades, hypermetric small saccades, quiver movements, hyper fast saccades can occur. Investigations Tensilon test: Intravenous injection of edrophonium is the gold standard for the diagnosis of ocular myasthenia. Edrophonium is a short acting anticholinestrase which increases the amount of acetylcholine available at the neuromuscular junction. In myasthenia this results in transient improvement of symptoms and signs such as weakness, ptosis and diplopia. Uncommon complications include bradycardia, loss of consciousness and even death. Lacrimation, salivation and abdominal cramps are mentioned as common minor side effects. The test should be done with a resuscitation trolley in hand if in case of sudden cardiorespiratory arrest. Objective baseline measurement of ptosis or diplopia with hess chart should be taken. Intravenous injection of atropine 0.3 mg is given to minimize muscarinic side effects. Intravenous dose of 0.2 ml
Fig. 16.1: Myasthenia
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containing 2 mg of edrophonium hydrochloride is given, if definitive improvement is noted the test can be terminated. If no response then the remaining 0.8 ml of 8 mg is injected after 60 seconds if there is no adverse reaction. The response lasts only for 5 minutes. Perverse reaction like worsening of the strabismus or a paradoxical response like right hypertropia becoming a left hypertropia after the injection is considered positive by some. Neostigmine Test • Intramuscular injection of neostigmine is useful in children. The effect lasts for 15 minutes to peak and lasts for only 30 minutes • Presence of acetylcholine receptor antibodies is virtually diagnostic of myasthenia gravis. Electromyography • Repetitive stimulation and single muscle fiber will show a decremented response • Sleep test is useful in neonates and babies. There will be improvement after sleep • Imaging the chest with the computed tomography or magnetic resonance imaging for the presence of thymoma. Differential diagnosis for myasthenia gravis: • Isolated or combined third, fourth, sixth or seventh cranial nerve palsies • Decompensated strabismus • Thyroid disease • Eaton lambert myasthenic syndrome • Botulism • Chronic progressive ophthalmoplegia • Myotonic dystrophy. Treatment Treatment of myasthenia gravis can be divided into—optical treatment, medical, and surgical treatment. Optical Treatment • Because of the variability of signs and symptoms it is difficult to treat. For binocular diplopia occlusion of one eye, but it makes the patient to view monocularly
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• Fresnel prism can be tried if the ocular deviation is stable for weeks • The crutch glasses are helpful in the case of ptosis. Medical Treatment • Anticholinergic drugs like pyridostigmine (60 mg) three times a day. One must be always aware of the cholinergic crisis if too much of pyridostigmine is given. The patient should be told to stop if bulbar symptoms or generalized weakness occurs. • Corticosteoids is used along with pyridostigmine. The patient should be maintained on steroids for months before tapering and should be a slow tapering for months when the patient is maintained on low dose of steroids there can relapse or unmasking of generalized myasthenia. • Immunosuppressant: Azathriopine is effective against myasthenia. It is given in the dose of 2-3 mg/kg/day • Cyclosporine A, plasmapheresis, mycophenolate and IV gamma globulin also can be used in generalized myasthenia. Surgical Treatment • Thymectomy is very effective for ocular myasthenia. The result of thymectomy for generalized myasthenia are very favorable with about 35 percent entering complete remission and 50 percent improving. • Eyelid surgery or ptosis and eye muscle surgery for diplopia are considered only if it is stable for few months and as a last resort. CHRONIC PROGRESSIVE EXTERNAL OPHTHALMOPLEGIA The clinical features are the involvement of the upgaze and then the lateral movements and may later be affected in all gaze resulting in a fixed globe. Because the muscle involvement is symmetrical, diplopia does not usually occur. There is also slowly progressive bilateral ptosis. Kearns-Sayre Syndrome • This is a mitochondrial cytopathy, inherited from the mother. • It is characterized by pigmentary retinopathy with coarse granularity. • Conduction defects of the heart can occur. Heart block may result in sudden death. • Other features are short stature, muscle weakness, cerebellar ataxia, neurosensory deafness, mental handicap and delayed puberty.
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Treatment Treat the associated conditions. Lubricants for the exposure keratopathy, base down prisms within reading glasses for reading if the down gaze is restricted.pacemaker may be required for the cardiac condition. In ocular pharyngeal dystrophy, for the dysphagia and aspiration cricopharyngeal surgery. Genetic counseling. MYOTONIC DYSTROPHY This is dominantly inherited in the gene of chromosome 19q. Usually manifest in the third decade. Peripheral muscle involvement which makes the release of grip difficult which can be tested with the Hand Shake. A mournful expression caused by bilateral facial muscle wasting. Slurred speech because of the involvement of tongue muscles and pharyngeal muscles hypogonadism, frontal baldness, intellectual detoriation, pulmonary and cardia complication can occur. Other ocular features are presenile cataract with polychromatic luster, ptosis, pigmentary retinopathy, light near dissociation, external ophthalmoplegia. ESSENTIAL BLEPHAROSPASM Blepharospasm can be a very disabling condition in terms of vision and social life. More commonly affects female in the older age group. This is a type of facial dystonia in which there idiopathic tonic contraction of orbicularis oculi. If it is secondary to any ocular pathology (corneal or conjuctival foreign body, trichiasis, blepharitis, dry eyes) then it is called secondary blepharospasm. Clinical Features • There is a bilateral involuntary lid closure which may be precipitated by stress, fatigue, social interactions. This is always bilateral. Disappears during sleep • Secondary ocular changes like ptosis or entropion can occur • This can be differentiated from hemifacial spasm which does not disappear during sleep. Treatment: Botulinum toxin given as multiple injections on the upper and lower lid. The effect generally last for 3 months time. In cases of secondary blepharospasm treat the underlying cause which is precipitating the blepharospasm.
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Fig. 16.2: Blepharospasm
Other treatment option are medical like benzodiazepine or surgical like myectomy. Meige’s Syndrome This is a blepharospasm with midfacial spasm. It may lead on to compromise of speech , eating and drinking. Breughel Syndrome This is associated with severe mandibular and cervical muscle involvement. Hemifacial spasm: This is a tonic clonic spasm of the musculature which occurs even during sleep. Usually affects the younger age group. It is thought to be caused by the irritation of the root of seventh cranial nerve by a compressive lesion. MRI of the cerebellopontine angle should be obtained to rule out tumor. Treatment It includes observation, botulinum toxin injection or neurosurgical decompression of the seventh nerve (Janetta procedure) Tourette’s Syndrome This includes multiple compulsive muscle spasms associated with utterances of bizarre sounds.
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Tic Douloureux Acute episodes of pain in the areas of distribution of the trigeminal nerve. Tardive Dyskinesia This is a orofacial dyskinesia, often with restlessness and dystonic movements of the trunk and the limbs. Ususlly it is associated with the long-term use of antipsychotic medication. Facial Myokymia Fleeting movements of the facial musculature which may be associated with stress, multiple sclerosis, caffeine or rarely tumors of the brain stem. Lid Apraxia • In lid opening apraxia there is total inhibition of the LPS with no activation of orbicularis oculi. This results in the lid closure with difficulty in initiating the lid opening. It is associated with parkinson’s disease, progressive supranuclear palsy, Huntington’s disease and Wilson’s disease. • Lid retraction and poor closure of the lids can occur in Parkinson’s, Parinaud’s and progressive supranuclear palsy. BIBLIOGRAPHY 1. 2. 3. 4.
Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005. American Academy of Ophthalmology- section 5- Neuro-ophthal 2004-2005. Jack J Kanski (6th ed) Clinical ophthalmology, Butterworth Heinmann 2007. Parson’s Diseases of The Eye (18th ed) Butterworth-Heinemann International editions. 5. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003.
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Miscellaneous Jeyalakshmi Govindan, S Soundari
PITUITARY TUMORS INTRODUCTION Pituitary adenomas occur most frequently between the fourth and sixth decade of life. Pituitary adenomas with secretory function can clinically manifest endocrine acivity. It can be either eosinophilic or basophilic. Eosinophilic adenomas secretes excessive amount of growth hormone producing acromegaly in adults and gigantism in the young. The hands and feet are enlarged, the jaws become prominent, the tongue is thickened, and the libido fails. Amenorrhea in the female and impotence in the male develop. Prolactin secreting adenomas results in galactorrhea and amenorrhea. Basophilic adenomas secrete ACTH and produce cushing’s syndrome. The clinical features of basophilic adenoma include adiposity, moon face, hypertension, hypogonadism and osteoporosis. Visual failure and field defects are less common with functional adenomas than with nonfunctional adenomas. Nonsecreting chromophobe adenoma is a highly common intracranial tumor. Pituitary hypofunction may be present in some cases. Headache is the most common neurological manifestation. Bursting headache is considered as the characteristic of pituitary adenoma. Loss of vision is the predominant ocular manifestation. The great majority of the visual symptoms consisted of visual loss in one or both eyes. The visual loss preceded other symptoms and signs such as headache and endocrinopathy in many patients.
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The location of the chiasma may be: Central chiasma: Chiasma lies directly above the sella , normally 80 percent of the individuals have central chiasma. Post fixed: Chiasma is located more posteriorly on the dorsum sella,present in 10 percent of the individuals. If there is a involvement from pituitary tumors the optic nerves are involved first. Prefixed: Chiasma located anteriorly over the tuberculum sella. If there is an involvement from the pituitary tumors the tract fibers get involved first. Present in 10 percent of the normals. If the chiasma is central both superotemporal fields are initially affected as inferonasal fibers pass low and anteriorly. As the tumor grows the inferior temporal field defect progress. The patient may not present until the central field is involved. Color desaturation across the midline is the earliest sign of chiasmal field defect. Optic atrophy is present in 50 percent of the patients. The other features which the patient can present with, is the seesaw nystagmus of Maddox and diplopia as a result of involvement of the cavernous sign and involvement of cranial nerve. Investigation • Coronal plane MRI is the investigation of choice • Endocrinological evaluation according to the clinical presentation. Treatment • Surgery for the pituitary tumor through transsphenoidal approach • Bromocriptine can shrink prolactinomas • Radiotherapy can also be used. CRANIOPHARYNGIOMA It is a slow growing tumor of Rathke’s pouch. It can interfere with the hypothalamic function resulting in dwarfism, delayed sexual development and obesity. As the tumor compresses from above and behind the inferotemporal field defects starts early as the upper nasal fibers pass high and posteriorly. MRI shows the location of the tumor. CT scan shows calcification in 60 percent of the cases. Treatment is mainly surgical. Postoperative radiotherapy may be helpful but recurrence are common.
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HEADACHE INTRODUCTION Headache is defined as pain in the head that is located above the eyes or the ears, behind the head (occipital), or in the back of the upper neck. Headache is a universal experience as over 90 percent of individuals have noted at least one headache during their lifetime. History The cause can usually be elicited from the history. Points to be noted are mode of onset, duration, frequency, location, nature of headache, prodromal symptoms, precipitating relieving factors and medical history and medication list. Omnious signs of headache include: 1. Abrupt onset, after 4th decade 2. Progressive symptoms 3. Focal neurological signs 4. Associated with fever, cough, straining 5. Change with position or exertion. Classification There are two types of headaches: Primary headaches and secondary headaches. Primary headaches are not associated with (caused by) other diseases. Examples of primary headaches are migraine headaches, tension headaches, and cluster headaches. Secondary headaches are caused by associated disease. The associated disease may be minor or serious and life threatening. Migraine A migraine is a common type of headache that may occur with symptoms such as nausea, vomiting, or sensitivity to light. In many people, a throbbing pain is felt only on one side of the head. An estimated 18 percent of women and 6 percent of men experience recurrent headache classified as migraine. It tends to start from age 10 but the peak prevalence is between the ages of 25 and 55.70 to 90 percent of migraine patients have a positive family history. Evidence suggests involvement of genetic factors in that defective gene encodes for a voltage dependent calcium channel that ultimately leads to neuronal excitability.
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Pathophysiology of migraine is not clearly understood. Evidence suggests the role of trigeminal –vascular projections and the neurochemical serotonin. The hyperexcitability of brain stem neurons is caused by release of vasoactive neuropeptides which also stimulate inflammatory cascade dilating meningeal vessels(pain) and activating portions of cortex(aura). Variour trigger factors that are thought to bring about migraine include certain foods, especially chocolate, cheese, nuts, alcohol, stress, sleep deprivation or birth control pills. Symptoms and Signs The headache usually begins in the fronto temporal region, unilateral but can be bilateral. The onset is usually gradual. The episodes may start after awakening and are generally relieved by sleep. The aura of headache precedes by 15-45 minutes. It may include • Scotoma (blind spots) • Fortification (zig-zag patterns) • Scintilla (flashing lights) • Unilateral paresthesia/weakness • Hallucinations • Hemianopia Classification of Migraine Based on Clinical Presentation 1. Common migraine (80%) (headache without aura) 2. Classic migraine (20%) (headache with aura) 3. Acephalic migraine
- Preceded by nausea, vomiting and autonomic symptoms - Preceded by visual or sensory dysfunction - Transient neurological events without headache occur over the age of 40. 4. Complicated migraine - Migraine with permanent neurological deficit. 5. Ophthalmoplegic migraine - Ipsilateral palsy of one or more extraocular muscles as the migranous headache is resolving. Common before the age 10. 6. Retinal migraine - Sudden monocular visual loss without flashes. Occasionally constriction of retinal arterioles and venules noted.
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7. Basilar migraine
- Bilateral blurring of vision, field defects, ataxia vertigo, nystagmus, dysarthria
INTERNATIONAL HEADACHE SOCIETY Criteria for Migraine Without Aura A. Five attacks fulfilling criteriaB-D B. Headache lasting for 4 to 72 hours(untreated) C. Headache has two of the following: 1. Unilateral 2. Pulsating quality 3. Moderate to severe intensity 4. Aggravated by physical activity. D. During headache at least one of the following: 1. Nausea or vomiting 2. Photophobia or phonophobia. Diagnosis Neuroimaging is rarely indicated in a patient with typical migraine and a normal examination. CT scan of the head is indicated to rule out intracranial mass or hemorrhage in selected or atypical cases. MRI and magnetic resonance angiography are more sensitive. They are useful if neurologic examination findings are abnormal, the migraine occurs for the first time after age 40 years, the frequency or intensity is increasing, and the accompanying symptoms of the attack change. Lumbar puncture is done when suspecting a diagnosis of subarchnoid hemorrhage, meningitis or pseudotumor cerebri. Treatment Symptomatic or abortive therapy is helpful when the attack occurs less than twice a week and short lived (Table 17.1). Prophylactic therapy (Table 17.2) is indicated when the headaches are more frequent or produce significant disability.Elimination of triggering factors contributes to prevention.
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Table 17.1: Abortive Therapy in Migraine Triptans NSAIDs Antiemetics Corticosteroids Miscellaneous
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Sumatriptan, Rizatriptan, Zolmitritan, Eletriptan Naproxyn, Indomethacin, ketorolac Droperidol, Prochlorperazine, Metoclopramide Prednisone, Methylprednisolone Acetaminophen, caffeine, Ergotamine, Butalbital
Table 17.2: Preventive Therapy in Migraine Beta blockers Calcium channel Blockers Antidepressants Anticonvulsants Miscellaneous
-
Propranolol, Nadolol Verapamil, Nifedipine
- Amitriptyline, Fluoxetin - Valproic acid,Topiramate - Lithium, Methysergide
Tension Headache It is the most common type of chronic recurring pain. Tension headache can be episodic or chronic. The pain is often described as pressure or tightness. It may occur under emotional stress or intense worry. Tenderness may be elicited in the scalp or neck. Criteria for Episodic Tension Headache A. At least 10 previous headache episodes for filling criteria B-D. B. Headache lasting for 30 minutes to 7 days. C. At least two of the following: 1. Pressure/tightening quality 2. Mild or moderate intensity 3. Bilateral location 4. No aggravation with physical activity. D. Both of the following: 1. No nausea or vomiting 2. Photophobia and phonophobia are absent. Treatment The abortive and prophylactic medications for migraine may be tried. The antidepressants nortryptiline and amitryptiline may be the first line agents for these patients. Botox injected into the frontal and occipital muscles has been tried in refractory tension headache.
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Cluster Headache Cluster headache, also known as histamine headache refers to a grouping of headaches, usually over a period of several weeks. Attacks usually are severe and unilateral and typically are located at the temple and periorbital region predominanatly occurs in middle ages men.Alcohol is common trigger.About 30 to 50 percent of patients will develop signs of Horner syndrome. Criteria for Cluster Headache A. At least five attacks B. Severe unilateral orbital,supraorbital or temporal pain lasting 15 to 180 minutes C. Headache associated with at least one of the following: 1. Conjunctival injection 2. Lacrimation 3. Nasal congestion 4. Rhinorrhea 5. Forehead and facial sweating 6. Miosis 7. Ptosis 8. Eyelid edema D. Frequency of attacks from one to eight per day. The major entity to exclude in a patient with painful horner syndrome is carotid dissection. Treatment The following may be tried in acute cluster attack: • 100 percent oxygen via a facemask • Subcutaneous or intranasal sumatriptan • Intranasal dihydroergotamine • Corticosteroids. Preventive therapies that are available are lithium, verapamil, methysergide. Headache and Ocular Diseases Headache due to ocular causes are often associated with periorbital pain and other eye signs. Some of them are given in the table.
Miscellaneous Ocular diseases
Examples
1. Corneal diseases Corneal erosions 2. Intraocular causes Scleritis, iritis, Angle closure glaucoma 3. Optic nerve diseases 4. Eye strain
Optic neuritis Uncorrected Hyperopic Refractive error, Convergence insufficiency
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Clinical features Severe pain and foreign body sensation on awakening Pain over the eye, tender to palpate and photophobia is universal pain on eye movements and eye may be tender Pain over the brow, spreading to scalp
The Differential Diagnosis of Headache Disorders Entity
Characteristics of pain
Subarchnoid hemorrage Brain tumor Hypertension Pseudotumor cerebri
Acute, occipital, worst ever, with meningismus Subacute dull ache with focal signs Acute frontal or occipital throbbing Subacute, dull, with transient visual loss and papilledema Acute or chronic, throbbing, with fever and meningism Throbbing pain over periorbital, with horner’s syndrome or ipsilateral visual loss Severe pain over the temple, tender Cough induced headache may be associated with posterior fossa lesions Throbbing, global in location after falling asleep, short lived in elderly
Meningitis Carotid dissection Temporal arteritis Cough headache Hypnic headache
FUNCTIONAL VISUAL LOSS INTRODUCTION An apparent loss of visual acuity or visual field with no substantiating physical signs;often due to natural concern about visual loss combined with suggestibility and a fear of the worst; best treated with reassurance. Functional visual loss (FVL) is frequently encountered in ophthalmic practice. Identifying such patients is extremely important in order to avoid unnecessary laboratory testing and secondary gain.
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Clinical Presentation • Binocular (rare) and monocular blindness • Decreased visual acuity (LP to 20/30) or fluctuating acuity on different visit • Visual field defects - monocular hemianopias, bitemporal and binasal defects, ring scotomas, tubular fields, spiral fields, starshaped fields • Diplopia • EOM paralysis • Paralysis, spasm and sluggish accommodation • Voluntary nystagmus • Total color blindness, non-recognition of Ishihara demo plate • Disturbances of reading and writing • Frequent blinking and blepharospasm • Ocular Munchausen’s syndrome FVL also has been reported in children due to underlying lack of parental attention or move to a different school. Tests for Functional and Simulated Defects The diagnosis can be made only with high degree of suspicion. The tests must be objective in nature. • Attitude of the patient: A patient with true vision loss tends to move cautiously, the hysterical patient move flawlessly; the malingerer will purposely bump into things. • Visual acuity: This is one of the most important tests as vision loss is the most common symptom of FVL. Varying test distance is a useful technique. • Pupillary reflexes: A patient who complains of total blindness with intact pupillary responses but no cortical lesion is likely to be functional. • Menace reflex: Blinking to visual threat • Stereopsis: Touching index fingers togther depends on proprioception and not on vision. • Optokinetic nystagmus: One eye observed ophthalmoscopically, while the drum revolves before the other. A slight nystagmus will be easily observed. • Head rotation nystagmus test: Head is rotated passively about 30° alternatively to right and left. The presence of vestibular nystagmus indicates true blindness. • VEP: The flash evoked visual potential can be used to document intact visual pathway.
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Tests for Simulation of Uniocular Blindness • Fixation test: Relies on refixation movement. A four diopter base out prism is placed infront of alleged blind eye. A true blind will show no refixation movement. • Diplopia test(Graefe’s test): The suspected eye is covered and uniocular diplopia elicited in the good eye by bisecting the pupil with the use of a strong prism.The suspected eye is then quickly uncovered and simultaneously the prism is slipped over the whole pupil of the other. If diplopia is still confessed malingering is proved. • Fogging test: Add progressively strong concave or convex lens in front of good eye as the patient reads. If reading continues vision with other eye is proved. • Color tests: Vectographic or duochrome visual acuity testing are also useful in patients with monocular complaints. Tests for Simulated Abnormal Visual Field • Monocular visual field defects: The most valuable instrument in the detection of FVL is the tangent screen as test distance can be varied. Patients with FVL typically manifest with tubular fields, i.e. the field remains the same size regardless of test distance. Also seen are spiraling and crossing isopters. • Binocular field defects: Standard perimetry is performed with both eyes open patient with FVL never realize the extent of nasal field of the contralateral eye.But automated perimetry does not definitely distinguish an organic defect from a functional one. • Central scotomas: It can be tested using the red Amsler’s grid and the red/green glasses.If the scotoma disappears when the red lens is over the affected eye and the green lens is over the good eye then the patient is functional. Differential Diagnosis • • • •
Amblyopia Optic neuropathies Retinal degeneration Cortical visual loss. When the diagnosis is uncertain MRI with contrast, ERG can be performed. Rarely neuroimaging with positron emission tomography may be done for suspected cortical visual loss.
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Management The successful management lies in physician’s empathy and encouragement. Emphasis must be laid on statements such as peripheral vision seems good and optic nerves are healthy. Treatment such as prescription of drops, low power spectacles and ‘retinal test’ where both eyes are patched and patient is isolated tend to satisfy them and improve the FVL. Finally psychiatric consultation is required in some patients. In children with FVL the prognosis for visual recovery is excellent.
OCULAR MANIFESTATIONS OF INTRACRANIAL ANEURYSMS INTRODUCTION The ophthalmologist may be the first physician to encounter clinical manifestations of intracranial vascular abnormalities that may herald devastating neurological complications. The common intracranial vascular abnormalities are intracranial aneurysms, carotid-cavernous fistulas and arteriovenous malformations. Intracranial Aneurysms An estimated 1 to 6 percent of the general population harbors an intracranial aneurysm. The annual rupture rate of aneurysms has been estimated to range from 0.05 to 2 percent, with a higher rate associated with a previous history of subarachnoid hemorrhage (SAH), symptomatic clinical presentation (mass effect or cranial neuropathy), large aneurysm size (>10 mm) or posterior circulation location. Subarachnoid Hemorrhage It is the most common manifestation in 90 percent of cases. 10 to 20 percent of patients presenting with aneurysmal subarachnoid hemorrhage (SAH) will die immediately prior to seeking medical attention. Others may develop papilledema, subhyaloid hemorrhage (terson’s syndrome), and paresis of lateral rectus of both eyes. Complications after SAH are rerupture, hydrocephalus, and delayed cerebral arterial vasospasm with ischemic neurologic deficits.
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Intracranial aneurysm can be congenital, saccular or berry aneurysm occurring in association with circle of Willis. The ocular manifestations depend on mechanical pressure on the structures nearby, sudden increase in size (>1 cm) and rupture. The unruptured aneurysms of the internal carotid, anterior communicating, posterior communicating and middle cerebral cause mass effect. The symptoms can be retro-orbital pain, third cranial nerve palsy, cavernous sinus syndromes, hydrocephalus, visual field deficits (Table 17.3), mild to moderate hemiparesis, or hypothalamicpituitary dysfunction. Carotid cavernous aneurysms are uncommon accounting for only 2 percent of all intracranial aneurysms. The aneurysm frequently involve the abducent nerve early. The pupil sparing third nerve palsy and ophthalmic(V1) involvement may also occur. The aneurysmal rupture result in carotid-cavernous fistula (see below) and rarely SAH. Diagnosis Transfemoral cerebral angiography is currently the “gold standard” for diagnosing intracranial aneurysms. An angiogram provides important information about site, size, direction of the aneurismal dome and neck, and relationship with the parent vessel and perforators. A transcranial Doppler study is useful in detecting the development of arterial vasospasm. A CT scan is important for establishing the diagnosis of SAH. An MRI scan is becoming an important tool for diagnosing a cerebral aneurysm. Currently, it will detect, with high reliability, aneurysms that are larger than 5 mm. This ability may be especially useful for monitoring a patient with a small, unruptured aneurysm. An MRI scan is also helpful in demonstrating the degree of intramural thrombus in giant aneurysms. In fact, magnetic resonance angiography may eventually replace transfemoral cerebral angiography. Table 17.3: Visual field defects due to intracranial aneurysms
Aneurysms
Visual field defects
Internal carotid artery
Nasal hemianopia on the affected side and temporal hemianopia on the other side bitemporal hemianopia From above bitemporal hemianopia Posteriorly homonymous hemianopia
Anterior and middle cerebral
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Management Surgical intervention is typically recommended for unruptured aneurysms (same as CCF below). Carotid-Cavernous Fistula Carotid-cavernous fistulas (CCFs) are abnormal communications between the carotid arterial system and the venous cavernous sinus. Mechanism of Direct CCF • Trauma (75%): High flow basal skull fracture • Spontaneous causes (25%): Low flow rupture of intracavernous aneurysm, neurofibromatosis, collagen vascular diseases and atherosclerotic disease Ophthalmic consequences of CCF are caused by compression and ischemia related to increased venous pressure and reduced arterial pressure. Clinical signs commonly associated with carotid-cavernous fistula include proptosis in 94% cases, pulsating exophthalmos (40%), bruit (75%), fronto-orbital headache, orbital pain (40%), chemosis (71%), extraocular palsy and diplopia (60%), loss of visual acuity (46%) 5th cranial nerve involvement in 24.6 percent cases and increased intraocular pressure and glaucoma. Causes of Glaucoma in CCF • • • •
Elevation of episcleral venous pressure Elevation of orbital pressure secondary to venous stasis and edema Secondary neovascular glaucoma Secondary angle closure from congestion of choroids and forward shift of lens iris diaphragm. Indirect CCF or Dural arteriovenous malformations result from communications between branches of internal or external carotid artery within the dura of cavernous sinus. They are most often seen in women over the age of 50 in association with systemic hypertension. Onset is insidious. The patient may experience diplopia and ophthalmoplegia (often from CN VI palsy), tinnitus or orbital bruit, and a red, congested eye that is often mistreated as an ocular infection or inflammation with arterialized conjunctival vessels and mild proptosis.
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Differential Diagnosis of CCF • • • •
Cavernous sinus thrombosis Retrobulbar hematoma Unrecognized intraorbital foreign body with cellulitis Tumor Diagnosis is accomplished through neuroimaging and arteriography. Contrast-enhanced CT scan and MRI will demonstrate a dilated superior ophthalmic vein and cavernous sinus. Ultrasonography may also demonstrate superior ophthalmic vein engorgement. Magnetic resonance angiography (MRA) is also very useful in identifying fistulas as well as particular vessel involvement. Arteriography is still the gold standard in identifying CCF with vessel involvement, but due to a small risk of morbidity and mortality associated with this procedure, we reserve this method for potential surgical cases (direct rupture of the ICA in high-flow CCF or highrisk dural CCF). Management High-flow CCF resulting from intracavernous rupture of the ICA, in 80-90 percent of cases without treatment result in blindness from central retinal vein occlusion or glaucoma. Other complications that may be seen are epistaxis, intracerebral hemorrhage and even death 99 percent treatment done by interventional neuroradiologist by placement of intravascular coils, carotid artery ligation or finally surgical clipping. Indications for Treatment • • • • •
Glaucoma Diplopia Intolerable bruit Severe proptosis causing exposure keratopathy Posterior segment ischaemia. Low-flow dural sinus CCF is very likely to resolve spontaneously in 20-50 percent of cases. In these cases, periodic observation is the best therapy. For exposure keratopathy artificial tears are prescribed and diplopia managed with occlusion therapy. Watch for clinical deterioration that indicates that a high-risk cortical venous drainage has developed.
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CONCLUSION Intracranial aneurysm is diagnosed with high index of suspicion that needs prompt referral to the neurosurgeons to facilitate early management and therapy. BIBLIOGRAPHY 1. Amar Agarwal. Handbook of ophthalmology; Slack USA 2005. 2. Bhatti, Tariq M, et al. Delayed Exacerbation of Third Nerve Palsy Due To Aneurysmal Regrowth After Endovascular Coil Embolization Journal of NeuroOphthalmology. 2004;24(1):3-10. 3. Carotid cavernous fistula Indian journal of otolaryngology and head and neck surgery 2005;57:65-67. 4. Catalano RA, Simon JA, Krohel GB, et al. Functional visual loss in children. Ophthalmology 1986;93:385-90. 5. Fahle M, Mohn G. Assessment of visual function in suspected ocular malingering. Br J Ophthalmol 1989;73:651-4. 6. Gilbert, Molly E Sergott, Robert C. Intracranial aneursyms Current Opinion in Ophthalmology. 2006;17(6):513-8. 7. Grant T Liu, Nicholas J, Steven L. Galetta Neuro ophthalmology Diagnosis and management philadelphia, Pennsylvania; W.B. Saunders Company; 2001. 8. Headache classification committee of the international headache society: Classification and diagnostic criteria for headache disorders, cranial neuralgias and facial pain. Cephalalgia. 1988-8 (suppl 7):1-96. 9. Hupp SL, Kline LB, Corbett JJ. Visual disturbance of migraines. Surv ophthal 1989;33:221-36. 10. Kline B, Frank J. Bajandas Neuro ophthalmology Review manual: Slack Incorporated 2004. 11. Lance JW. Current concepts of migraine pathogenesis. Neurology 1993;43 (suppl 1): S11-S15. 12. Miller NR, Keane JR. Walsh and Hoyt’s clinical neurophthalmology. Baltimore, Williams and Wilkins, 1998. 13. Peyman-Sanders-Goldberg-third volume-principles and practice of ophthalmology. 14. Sunita Agarwal, Athiya Agarwal, et al. Textbook of ophthalmology; Jaypee, India 2003. 15. Walsh and Hoyt’s clinical neuro ophthalmology Neil miller and Nancy Newman 6th edition 1995 Lippincott Williams.
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Examination of a Neuro-ophthalmology Case S Soundari
HISTORY Examination of a neuro-ophthalmology case is crucial.1-4 • Onset of the visual loss “its progression and the severity” whether associated with pain • Any history of headache, vomiting • Anyaura with the headache • Eye pain: Whether associated with visual loss • Double vision: onset, for distance and near, which direction it is more • Involuntary movements of the eyeball • Balck outs • Color vision defect • Drooping of the eyelids: Onset, whether it is constant or variable • Any associated double vision, progression and associated features • Any field defects. Past History • • • • • •
History of medical diseases like diabetes milletus, hypertension Whether on any drugs for long-term like ATT Any thyroid eye disease Myasthenia Any treatment history like radiotherapy and chemotherapy Any past CNS problem.
Examination Best corrected visual acuity: The processs of examination begins with assessment of visual acuity, the most common measure of the central visual function is the best
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corrected visual acuity which measure the maximal foveal spatial discrimination, should be obtained with refraction vision should be tested for both distance and near. Color Vision – by Pseudo-Ishihara’s Chart Testing of color vision compliments assessment of visual acuity. In optic nerve disease, particularly optic neuritis, the degree of dyschromatopsia may be proportionality greater than the degree of smaller visual acuity loss. In macular diseases, acuity and color vision tend to decline to corresponding degrees. Persistent dyschromatopsia is common even after recovery of visual acuity in optic neuropathy. Pseudoischromatic plates are commonly used clinically as a gross test of color vision because opticneuropathies often manifest prominent red-green defects. Pupil Examination • • • •
Direct light reflex Indirect (consensual) light reflex Swinging flash light test Near reflex.
DIRECT LIGHT REFLEX • The light reflex is tested in dim light with the patient looking at a distant target to neutralise the near reflex • The bright light is brought from the side for the right eye. The pupil will constrict to the bright light briskly • The same is repeated now for the other eye. INDIRECT LIGHT REFLEX The eyes are separated by placing a hand in between the right and the left eye. The patient is asked to fixate at the distant object. The light is shown to the right eye and the response is seen in the left eye and the vice versa. SWINGING FLASH LIGHT TEST The test is done in dim illumination and the patient focusing at the distance object. The examiner alternatively illuminates both eyes with a relatively bright light. Constant distance, constant duration of the illumination and light intensity should be maintained so that both eyes must adopt the same conditions.
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When the pupil constricts more slowly and dilates rapidly is called as relative afferent pupillary defect NEAR REFLEX Near reflex is the triad of: • Convergence • Accomodation • Constriction of the pupil. The near reflex is tested by asking the patient to look at the distance and to bring the focus to with in 10 cm of the eye. Confrontation Visual Fields Make the patient sit opposite to the examiner at 1 meter at the same eyelevel. Patient should be able to appreciate the object used for testing the visual fields, for the peripheral visual field. Each eye has to be tested separately instruct the patient to cover the left eye and look into the examiners right eye. Present the finger in each quadrant to test quadrantanopia. For checking the central field: Red pin is used. The pin is brought towards the center from each quadrant and the ask the patient to comment about when he is seeing the pin red. Ask the patient to tell again when the red becomes faded or disappeared as the pin is moved inwards. Where the pin has disappeared from that point move the pin in all directions till it is seen in each direction. This maps out the blind spot. For color desaturation two red objects should be presented simultaneously and compared. Ocular Movements Shine the torch light into the patients eye form from front and look for any obvious tropia. Look for any abnormal head posture or ptosis Torch light can be used and it should be moved in all nine diagnostic positions and look for any obvious deviation and nystagmus. Saccades have to be performed both in the horizontal and vertical directions. This is performed by showing patient fist and an object placed for apart. The patient is asked to look from the fist to the object alternatingly. Convergence: An object is moved from 50 cm towards the patient. Normal people will achieve a near point at 10 cm. If there is any obivious deviation then diplopia charting and hess charting are done.
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Diplopia Charting In a dark room, a red glass is placed before one eye and a green before the other to distinguish their images. A bar of light through a stenopalic slit in a hand torch is then moved about in the field of binocular fixation at a distance of at least 120 cm from the patient, the patients head being kept stationery. The positions of the images are accurately recorded upon a chart with nine squares marked upon it. The follow data are derived from diplopia charting of: i. The area of single vision and diplopia. ii. The distance between the two images in the areas of diplopia. iii. Whether the images are on the same level or not. iv. Whethere one image is inclined or both are erect. v. Where the diplopia is homonymous or crossed. Test is purely a subjective one. The positions of gaze where the separation of the images is maximal is found. In that position of gaze, the furthest displaced image belongs to the eye with the muscle palsy. Hess Charting To measure the degree of deviation, especially if torsional and particularly to measure any progressive increase, the Hess screen is used. It consists of a tangent screen marked in lines on a black cloth with spots at the intersection of 15o and 30o lines with themselves and with the horizontal and vertical lines. The patient wears a red-green filter goggles and holds a green light projection pointer. First red in front of right eye. The examiner holds a red light projection pointer onto the screen at those spots. The patient is asked to super impose the green light into the red light. In normal circumstances, the two pointers should be nearly super-imposed in all nine positions of gaze. The goggles are then reinversed with red in front of the left eye. The eye with the green filter is the one, which is tested. It is useful as a prognostic guide. If the paresis of the muscle persists, then the shapes of both charts will change as follows: 1. Secondary contracture of the ipsilateral antagonist will develop, which will show up on the chart as an overaction. 2. This will lead to a secondary (inhibitional) palsy of the antagonist of the yoke muscle, which will show as underaction. With further passage of time, the two charts become more and more concomitant, until it may be impossible to determine which was the primary pareitic muscle.
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Nystagmus Observe for any abnormal head posture for maintaining in the null position. Nystagmus to be observed in the primary position. Its plane like horizontal, vertical, rotatory or see saw to be noted. Its type like whether it is jerky or pendular. Its direction, the fast phase of the nystagmus and its amplitude whether it is fine, medium or coarse. Ocular motility is then performed and look for dampening of the amplitude with convergence when the eye accommodates. Cover test to be performed to identify manifest nystagmus. Fundus Examination • To look for margins—whether blurred or well defined, its color whether normal pink color hyperemia or pallor • To look for abnormal vasculature like optociliary shunt • And to look into the macula for the evidence of neuroretinitis. Visual Fields Visual loss necessities visual field testing, which aids in localizing the lesion along the affluent visual pathway and quantifies the defect. Both kinetic and static and kinetic techniques are important. Testing may be considered qualitative (looking for the pattern of any visual field abnormality) or quantitative (measuring the degree of damage). All points of the equal threshold may be connected to form an isopter. This contour map represents the outer limits of visibility. Scotomas are areas of depressed visual function surrounded by normal visual function. Nerve fibres from the two eyes decussate in the chiasm. Lesions at the chiasm result in damage to the nasal crossing fibers and corresponding impairment in the heteronymous temporal visual fields as Bitemporal hemianopia. Lesions that injure one optic nerve at its function with the optic chiasm produce the anterior chiasmal syndrome with functional scotoma where there is a central visual field loss in one eye accompany a supero-temporal defect in the opposite eye. As the fibers course in the retrochiasmal visual pathway (Optic tract, temporal lobe, parietal lobe and occipital lobe visual radiation). Crossed nasal fibers from the controlateral eye and uncrossed temporal fibers from the ipsilateral eye run together. Damage results in homonymous field defects. Anterior lesions produce incongruous defects and the posterior damage results in progressively congruous defects.
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Other Cranial Nerve Examination First Cranial Nerve Tested by covering each nostril in turn and presenting the patient with familiar smell like coffee. Irritants must not be used as it stimulates the trigeminal nerve. Second Cranial nerve Visual acuity, pupillary reaction, visual fields, visualizing the optic nerve head. Third, Fourth and Sixth Cranial Nerves Examination of the ocular motility in all nine diagnostic positions. Fifth Cranial Nerve • Motor part is tested by palpating the temporalis and the muscles of mastigation when the patient clenches his teeth • Sensory part is tested by checking for light touch in the three dermatomes corneal reflex to be tested. Seventh Cranial Nerve • Patient is asked to wrinkle his forehead, smile and blow his mouth. • Attempt to open the eyelids with eyes closed and to look for bell’s phenomenon. Eighth Cranial Nerve Perform the webers and the rinne’s test by using tunning fork. Ninth and Tenth Cranial Nerves Gag reflex can be done. Ask the patient to say Ah and to look for any deviation. Eleventh Cranial Nerve Patient should be able to shrug the shoulders against resistance and to rotate the head against resistance. Twelfth Cranial Nerve Make the patient put out his tongue and observe for wasting and deviation.
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CNS Examination • Orientation to time place and person. Memory both short and long term memory • Tone of the muscle to be checked • Power of the muscle to be graded — Grade 0–no movement — Grade 1–flicker movement — Grade 2–presence of movement when gravity is eliminated — Grade 3–movement against gravity — Grade 4–movement against resistance but power not full — Grade 5–full muscle power. Reflexes • Both superficial and deep reflexes to be elicited • Biceps, triceps, supinator and finger reflex for the upper limbs • Knee jerk, ankle jerk and babinski reflex for the lower limb. Coordination • Finger nose test and to look for disdiadokinesia for the upper limb • Getting the patient to put his heel on the shin and run it up and down for the lower limb. Sensation • • • • •
Pin prick and temperature Joint and position sense Vibration sense Observe the patient for the gait Spastic gait, wide based gait.
REFERENCES 1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee, India 2003. 2. Amar Agarwal. Handbook of ophthalmology; Slack USA 2005. 3. Parson’s Diseases of The Eye-(18th ed)-Butterworth-Heinemann International editions. 4. American Academy of Ophthalmology- section 5- Neuro-ophthal 2004-2005.
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Imaging in Neuro-ophthalmology P Ramesh
COMPUTED TOMOGRAPHY Principles Computed tomography (CT) was the first modern imaging technique which was able to distinguish different soft tissues by measurement of their different densities. The basis of this technique is the measurement of different absorption values after exposure to X-rays. In the slice of interest, the absorption values of parts of a defined matrix (so-called voxels) are transformed to gray-scale units by specific algorithms, the reconstruction is shown on a display, and all data are sampled in a digital manner. The absorption value is named after its inventor as the Hounsfield unit (HU) (Hounsfield 1973). It varies linearly in proportion to the absorption coefficient and is defined arbitrarily: thus, water is defined at 0 HU, air may have –1000 HU and less, and in bone, values of more than +1000 HU are measured. The mean values of fat range from –20 to –100 HU, cerebrospinal fluid (CSF) shows about 4–10 HU, and brain parenchyma normally presents as 35 HU (white matter) to 45 HU (gray matter). CT, along with MRI and ultrasound (for orbital pathologies), is one of the so-called noninvasive imaging modalities. It remains the method of choice for intracranial emergency screening, also for suspected fractures, and when an analysis of possible bony changes, e.g., a calcification is helpful or essential for the decision of the differential diagnosis. The distinctly different X-ray absorption of bone, fat, muscles, vitreous body, and lens represents a very good natural intrinsic contrast of the different orbital tissues.
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Contrast Medium In normal extracranial parenchymal tissue (e.g., the lacrimal gland) the effect of diffusion of iodized contrast material out of the lumen of capillary vessel into the extracellular space is seen as increased density (>10 HU). As a result of the sum of all contrast medium-filled capillaries with an intact blood-brain barrier (BBB), the contrast enhancement of normal brain parenchyma is only 3–5 HU. The BBB represents a property of the pial vessel, where the tight junction of their capillary endothelium prevents a passive diffusion of macromolecules, such as water-soluble contrast medium (Sage and Wilson, 1994). In case of a breakdown of the BBB, whether caused by a tumor or an infection, the continuous endothelial tight junctions are destroyed, and the extravasation of contrast medium into the pathologic process leads to a contrast enhancement (> 5 HU). In CT examination of the orbit, the indication of IV contrast is limited to suspected vascular lesions, as differential diagnosis is mainly led by morphological changes. If indicated, two main contraindications should be considered: 1. A distinct renal impairment may lead to renal failure. The risk of contrast agent-induced renal failure is high in dehydrated patients, in those with a known renal or cardiovascular insufficiency, and in those suffering from plasmocytoma, hypertonus, and hyperuricemia (Katzberg, 1997). Especially in patients with diabetes mellitus and an additional renal insufficiency, the risk of contrastinduced renal failure is about 9 percent (Parfrey et al. 1989). Although no absolute limiting value can be defined, the serum creatinine should not exceed >1.5 mg/dl, and the use of nonionic contrast agent should be standard (Schwab et al. 1989; Uder 1998). 2. In case of a manifest or known history of hyper-thyreosis, an application of iodized contrast material should be avoided. If imperatively necessary, it should be applied only after blockage of the thyroid, in order to avoid a thyrotoxic crisis, still a lifethreatening disease (Kahaly and Beyer 1989). It is recommended to start prophylactic medication at least 2–4 hours before the application and continue it for 14 days, at a dosage of 900 mg perchlorate per day. In patients at risk, a facultative medication with 20 mg Thiamazol per day can be administered additionally (Rendl and Saller 2001). A known allergic reaction to iodine represents a relative contraindication, as short-term medication with H1- and H2-blockers immediately before the exposure to iodized contrast medium can prevent this complication (Wangemann et al. 1988).
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MRI Basic Physical and Technical Principles of Relaxation, Special Sequences Magnetic resonance imaging (MRI) is a method to generate crosssectional images from the interior of the body based on the physical phenomena of nuclear magnetic resonance without using ionizing radiation. Atomic nuclei such as those of 1H, 13C, 14Na, 19F, 23N, and 31P with an odd number of protons and/or neutrons have a magnetic dipole moment. Hydrogen nuclei are abundant in biological tissue, as in the hydrogen atoms of water molecules. This is the reason for the use of hydrogen nuclei in medical MRI. Without the influence of an external magnetic field, the directions of the innumerable single dipoles are randomly arranged such that they cancel each other out, resulting in no macroscopic magnetic dipole moment. However, in the presence of an external static magnetic field, the small nuclear magnetic dipoles tend to align in the direction of the field, like a compass needle to the magnetic field of the earth. The nuclear magnetic dipoles are not aligned statically, rather they are staggering around the direction of the external static magnetic field. This phenomenon can be compared with the tumbling of a top around the direction of the gravitational force. This movement is called precession. The number of revolutions of this precession, designated Larmor frequency, depends on the magnetic moment of the nucleus and the strength of the external magnetic field applied. In case of a 1.5-T MRI scanner, the Larmor frequency of the hydrogen nuclei is 63.87 MHz. This characteristic allows the transfer of energy from an external radiofrequency pulse to the nuclei provided that the frequency is precisely the same. This means that there is a resonance between the transmitter and the macroscopic oscillating magnetic moment, which acts as the receiver. During energy absorption, the precessing nuclear spin axes circumscribe a cone that becomes increasingly flat. This can be illustrated as an exciting nucleus that opens its umbrella. The Brownian motion of molecules leads to a continuous rearrangement of the dipoles, such that statistically only one per million (5 ppm: parts per million) of the hydrogen nuclei are aligned with the direction of an external 1.5-T field at room temperature. After the termination of the applied radiofrequency pulse, the macroscopic magnetic field returns to its prior state by emitting simultaneously decreasing electromagnetic waves with the precessional frequency. These waves emitted during the relaxation are measurable and represent values which are attributed to the brightness of the individual pixels (picture elements) of which the images are composed by the application of sophisticated mathematical reconstruction algorithms.
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There are two types of relaxation. One is the signal decay of the sum vector parallel to the strong external magnetic field, which is termed the longitudinal relaxation or the T1 relaxation. During the T1 relaxation (spin-lattice relaxation), the excess energy is transferred from the nuclei to the environment (the term lattice is derived from crystalline solids and is used here in a broader meaning). The other relaxation is the signal decay of the sum signal vector perpendicular to the strong magnetic field and is designated the transverse or T2 relaxation. In T2 relaxation, there is a dispersion of the primarily synchronized precessional rotation of the spins. One can imagine the spins as an ensemble of ballet dancers, who initially obey the instructions of the maestro and start all in the same position (they are in phase). After this moment, they show a lack of discipline, and each ballet dancer turns a little faster or slower than the others (loss of coherence), resulting in a random distribution of the positions (out of phase). If we return to the spinning direction, at the beginning of this process we can record the net sum vector of all synchronized (in phase) individual spins, with a rapid decay as they go off phase. The loss of coherence is caused by minute local magnetic inhomogeneities around the macromolecules. As the adjacent spins also exchange excitation energy with each other, T2 relaxation is termed spin-spin relaxation. Signals registered from the biological tissue depend on the water or proton concentration that can be excited and on the relaxation characteristics. Pure or so-called free water would show a high concentration of excitable protons and a slow relaxation caused by only slightly restricted tumbling of small molecules. On the other hand, protons bound to macromolecules would show a fast relaxation by dissipating their energy to the environment and a loss of coherence. The MRI characteristics of tissue are defined by the composition of these components, represented in this paper in a simplified manner. Manipulation of the MRI examination parameters enables us to enhance the differences between the local tissues, resulting in a better inherent contrast. The terms T1-weighted (T1w), proton density-weighted (PDw) or T2-weighted (T2w) characterize MRI sequences or images and define the more pronounced biophysical effect of the specific image information. Proton density (PD)–weighted images are similar to T2-weighted images, but have a shorter echo of 10–50 m and are less dependent on the relation than on the concentration of protons, i.e., water concentration in the tissue (Bösiger 1985). The fluidattenuated inversion recovery (FLAIR) sequence combines T2weighting and suppression of the so-called free, not tissue-bound water.
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After intravenous administration of a MRI-specific contrast medium, such as gadopentate dimeglumine (biologically inert as complexly bounded gadolinium, i.e., GD-DTPA® or GD-DOTA®), a different take-up by tissues is seen, analogous to the iodized contrast medium used in CT. The use of contrast medium (in T1-weighted sequences) can further improve the contrast between anatomical details and also between normal and pathological tissues because of its different signal enhancement. If these contrast-enhancing structures are embedded in primarily hyperintense tissue (such as the extraocular muscles, or potential lesions within the retro-orbital fat) the signals will interfere, resulting in a loss of tissue contrast between the anatomical components. This problem can be solved using a pulse sequence that suppresses the high signal of the native hyperintense tissue. In the case of fat, the sequence is designed to be fat-suppressed (FS). Special MRI protocols enable a differentiation of flowing blood from nonmoving tissue (so-called stationary tissue), the basis for MR angiography. In MR angiography, the signal of stationary tissue is suppressed and the signal of flowing blood is enhanced, without any application of contrast material. The so-called diffusion-weighted MRI (DWI) is able to image molecular diffusion. Tissue-bound water has a restricted molecular diffusion compared with free water, due to frequent collisions with macromolecules, in particular proteins. Therefore, tissues with a different viscosity and a different ratio of intra- and extracellular spaces show different diffusion properties. For this reason, diffusionweighted MRI discriminates reliably an arachnoid cyst filled with free water and an epidermoid tumor of solid tissue whereas in conventional sequences, liquor and epidermoid tumor can both give the same signal intensity (Laing et al. 1999; Gizewski 2001). The so-called anisotropic diffusion of water molecules in the fiber pathways, which is much more restricted across the fibers than along them, can also be imaged in different planes (Hajnal et al. 1991). Diffusion-weighted MRI can disclose an acute infarction at a very early stage, and in the case of elderly patients with multiple chronic infarctions, it helps to uncover additional new lesions (Schaefer 2001). It also seems that diffusion-weighted sequences image a cystic tumor different to the central colliquation of an abscess, so offering an additional tool in the differential diagnosis (Kim et al. 1998). Along with a strong and very homogeneous main magnetic field and all devices (antennas or coils) to excite the protons by a radiofrequency pulse and to receive the electromagnetic waves emitted from them, there is a need for a space-encoding system. Temporary,
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superimposed, magnetic gradient fields cause changes of the Larmor frequency and the phase of spin populations in small volumes (voxels), with a precise local attribution. Where the magnetic field is stronger, the precessional frequency is higher, and where the magnetic field is weaker, the frequency is lower. It is possible to identify the location of signal generating spin pools by small space-encoded differences of the frequencies, like distinguishing radio stations. Additional spaceencoded different phases of precessing spin pools are used. For more superficially located structures, such as the orbits, the image resolution can be optimized by using phased-array surface coils instead of the conventional head coil. Surface coils are specially designed antennas, which can be applied near the region of interest and fades out disturbing signals from the environment. In case of an examination of the orbit, they are placed obliquely over both orbits, in order to lighten the orbital apex. It should be emphasized that a relatively small unilateral surface coil (with a diameter of about 4 cm) applied anteriorly over one orbit is only suitable for imaging the ipsilateral globe and does not provide a more posterior “illumination”. Restrictions Ferromagnetic Material, Pacemaker, Neurostimulator, Ventricular Shunts with magnetically adjustable valves. When approaching the temperature of absolute zero, no electrical resistance as e.g., in the coil of the electric magnet is found. For this reason, the most frequently used modern high-field MRI scanners (0.5–1.5 T) today are based on a superconducting coil of the main magnet, a system with a liquid helium-cooled main coil. This strong main magnetic field necessitates a few precautions. Patients with ferromagnetic implants, e.g., older aneurysm or other vessel clips, pacemakers, neurostimulators, and traumatically incorporated metallic-ferromagnetic foreign bodies (e.g. debris arising from working with metal, or old shell splinters), should not be exposed to high-field MRI. In addition to the image quality disturbance caused by the so-called susceptibility artifacts of the ferromagnetic material (Lüdeke et al. 1985) this can endanger the patient (Kanal and Shellock 1993). Whereas metal devices fixed on bone do not present a danger if exposed to MR, ferromagnetic foreign bodies, or clips in the lung, abdomen, eye, and adjacent to vessels can twist due to the strong main magnetic field and lead to a life-threatening complication. Ventricular shunts with transcutaneous magnetically pressureadjustable valves (Medos and Sophy valves) can be maladjusted in MRI, and therefore the systems have to be checked radiologically
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after MRI (Miwa et al. 2001; Ortler et al. 1997). As new magnetcompatible devices (Wichmann et al. 1997) have only been developed in the last decade, MRI is still unavailable to most patients with an implanted pacemaker or neurostimulator. The problems are not only caused because of the fact that these devices are usually magnetically programmable, there is an additional risk from the electrodes, which can act as antennas and interact with the changing electromagnetic fields. One must be always absolutely certain about the individual patient’s magnet compatibility, probably with the result of a rejection of the patient for MRI if there remains any doubt. Claustrophobia, Sedation, Surveillance To perform a MRI examination, it is necessary to bring the entire patient into the narrow shaft of the equipment, as the optimal homogeneity of the magnetic field is in the center of the magnet. Even for an examination of only the head or the orbit, the patient has to be placed deep inside the MRI. This is mainly a problem for claustrophobic patients, and thus they need sedation before the MRI examination. However, a sedated patient placed in this narrow tunnel is not accessible. In case of deep sedation, special magnet-compatible monitoring devices are needed for surveillance, including at least essential peripheral pulse oximetry. In MRI, the acquired data are not separately sampled sections, as for CT, but the data sampling is simultaneous for all sections of one sequence and the acquisition time depends on the examination parameters, e.g., the repetition time chosen. Therefore, one MRI sequence may last only a few minutes or even more than 10 min. If the patient moves during this time, a loss of image quality of all sections results. During MRI of the orbit, the patient should keep the eyes open and try to maintain a midline resting position. Consequently, in the case of uncooperative patients, who are not able to remain motionless, the quality of the images will be impaired. Optic Pathway Pathology • • • •
congenital pathology/infantile presentations acquired optic pathway lesions work-up in systemic diseases unexpected (incidental) fi ndings Any neuroimaging procedure should be based on profound clinical (including ophthalmological if appropriate) examination. This should allow the neuroradiologist to formulate specific questions.
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CONGENITAL PATHOLOGY OF OPTIC PATHWAYS Infantile Presentations Micro-ophthalmos/Anophthalmos Uni- or bilateral micro-ophthalmos/anophthalmos may be seen in various conditions (Albernaz et al. 1997; Nelson et al. 1991). Neuroimaging is performed to assess orbital anatomy, optic chiasm, and posterior visual pathways as well as possible brain malformations Aicardi syndrome, observed only in girls, is considered to result from an X-linked mutation that is lethal in boys. The relevant triad consists of a typical optic disk appearance with “chorioretinal lacunae”, infantile spasms, and agenesis of the corpus callosum (Aicardi 1992; Brodsky et al. 1995). In addition, other central nervous system malformations are always present, in particular migration anomalies (heterotopias, polymicrogyria) and midline arachnoid cysts. Ocular Tumors Retinoblastoma is the most common intraocular tumor in infancy, affecting about 1 in 20,000 infants. The most frequent presenting symptom is leukokoria, also called “cat’s eye reflex”. Leukokoria generally represents an advanced stage of the disease. Computed tomography (CT) (Fig. 19.1) displays punctate or more homogeneous areas of calcification in 95 percent of retinoblastomas (Barkovich 1995). Contrast enhancement of tumor tissue is generally found. Contrast enhancement is also demonstrable with MRI. T1-weighted images reveal the tumor as hyperintense, T2-weighted images usually as a hypointense mass Proton density images may assist in the demarcation of the tumor. MRI can occasionally provide evidence of distal optic nerve infiltration. A large proportion of retinoblastomas are genetically determined, and about a third occurs bilaterally. When tumoros tissue is also demonstrated in the pineal region by neuroimaging, it is termed trilateral retinoblastoma. This may already be present on initial evaluation. Spasmus Nutans So-called spasmus nutans typically presents at 6–12 months with disconjugate nystagmus, torticollis, and findings have been seen in girls.
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Figs 19.1: CT scan showing trilateral retinoblastoma
Other White Matter Disorders Apart from PMD, other dysmyelinating conditions can present with congenital nystagmus. The exact genetic/biochemical basis of these rare conditions is still unknown. Septo-optic Dysplasia Septo-optic dysplasia (SOD) typically presents as congenital nystagmus. Fundus examination reveals bilateral optic nerve hypoplasia. In addition, the syndrome consists of an absence of the septum pellucidum (Hypothalamic-pituitary dysfunction is present in a minority of patients, presenting as neonatal hypoglycemia and/or growth retardation (Sorkin et al. 1996). The prognosis is quite variable, ranging from blindness to useful vision. Affected children may be mentally retarded. In some children, additional CNS malformations can be found, in particular hypoplasia of the corpus callosum and cortical dysplasia (Sener 1996). SOD is unlikely to be a homogeneous entity. Hypoplasia of the optic nerves and absent septum are also seen as part of the holoprosencephaly complex (Barkovich 1995). The septum pellucidum is also mostly missing in rhombencephalosynapsis. It is suggested that SOD is a vascular disruption sequence (Lubinsky 1997).
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Optic Nerve Hypoplasia Hypoplasia of the optic nerves may be unilateral or bilateral (Figs 19.2 and 19.3). It is not a clinical or pathogenetic entity. We have seen several children with unilateral optic nerve hypoplasia presenting to the ophthalmologist with “poor vision” or strabismus. The intracranial anterior optic pathways are usually markedly asymmetric, but additional anomalies are exceptional.
Figs 19.2A and B: (A) Axial, (B) coronal T2-/FSE MRI of a 3-month-old-girl without visual fixation. Absent septum pellucidum and almost no identifiable optic nerves. Diagnosis: septo-optic dysplasia
Figs 19.3A and B: Patient clinically blind at 1 year (A) Axial, (B) coronal T2-/FSE MRI of a 4-year-old boy. Clinically convergent strabismus and bilateral optic nerve hypoplasia. MRI shows absent septum pellucidum. Diagnosis: septo-optic dysplasia
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Periventricular Leukomalacia Periventricular leukomalacia (PVL) is a well-known complication of prematurity before 34 weeks’ gestational age. PVL affects primarily the posterior part of the hemispheric white matter. Clinically, it may go along with spastic diplegia type of cerebral palsy and is often accompanied by delayed visual development (Jacobson et al. 1996; Lanzi et al. 1998; Olsen et al. 1997). MRI allows the detection of specific residual findings: variable reduction of periventricular white matter predominantly involving the posterior aspects, increased size of lateral ventricles, often with an irregular contour (evacuo). The remaining white matter often shows increased T2 signal, presumably corresponding to gliosis. Multiple Sclerosis It is estimated that about 2 percent of patients with multiple sclerosis (MS) present during childhood. Presenting symptoms may be variable such as muscular weakness, gait abnormalities, visual symptoms, and seizures (Ghezzi et al. 1997; Hanefeld 1992). Imaging findings in pediatric MS are not considered to be different from those in adults (Barkovich 1995). Acute Disseminated Encephalomyelitis Acute disseminated encephalomyelitis (ADEM) or parainfectious encephalomyelitis is considered an autoimmune response. This hypothesis is supported by the fact that the gross pathologic and histologic manifestations resemble those of experimental allergic encephalitis. ADEM involves primarily white matter but can also affect cortical and deep gray matter. Children typically develop acute focal neurologic signs and/or seizures late in the course of a viral illness or post vaccination). Neuroimaging reveals usually multiple foci of T2 hyperintensities; these may be circumscribed, confluent, or occasionally affect white matter diffusely (Murthy 1998). Various patterns of contrast enhancement may be found in the acute/subacute phase. Differentiation of MS from ADEM is not always possible in the beginning. The prognosis of ADEM is favorable as a rule, leading to complete clinical recovery, both from the clinical and the neuroimaging points of view. Occasionally, sequelae can be found. Trauma (Nonaccidental Injury) Injuries to the optic pathways due to head trauma will not be discussed here. However, we would like to point to so-called nonaccidental
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injury by shaking infants less than 6 months of age. The typical presentation is impaired consciousness and convulsions, often resulting in status epilepticus. Typically, bilateral retinal hemorrhages are present. Extensive cerebral damage in this condition usually results in permanent neurological sequelae including visual impairment or even cortical blindness (Ewing-Cobbs et al. 1998). The neuroimaging correlation in the acute stage is not spectacular, with evidence of brain swelling and often some interhemispheric blood accumulation. Followup neuroimaging as a rule demonstrates extensive cerebral atrophy. Neurofibromatosis Type 1 Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder due to mutations in the very large NF1 gene at chromosome 17q11. About 50 percent of patients have new germ-line mutations, i.e. they have no positive family history. The prevalence in most populations is about 1:4000 individuals. As is evident from the listing of diagnostic criteria optic pathway glioma (OPG) is such a criterion. OPG are tumors of infancy; in larger series, the mean age at diagnosis is 4–5 years (Figs 19.4A and B). Diagnostic criteria for neurofibromatosis type 1 The presence of two or more of the following is diagnostic: 1. Six or more café-au-lait spots, greater than 5 mm in diameter in prepubertal children and over 15 mm in post-pubertal individuals. 2. Two or more neurofibromas of any type, or one plexiform neurofi broma. 3. Axillary and/or inguinal freckling. 4. Optic nerve glioma. 5. A distinctive osseous lesion, such as dysplasia of the sphenoid wing, thinning of long bone cortex, with or without pseudarthrosis. 6. A first-degree relative (parent, sibling, or offspring) with NF1 according to the above criteria. OPG are pilocytic astrocytomas. It is important to distinguish astrocytomas from benign lesions commonly encountered in NF1: T2 hyperintensities are often found in the basal ganglia (particularly globus pallidus), brainstem, and cerebellum, not enhancing with contrast and not having space-occupying effects. Mild proptosis is not uncommon in NF, even in the absence of an optic nerve glioma. It can be related to sphenoid wing dysplasia, but often no obvious explanation is evident. Neurofibromatosis Type 2 Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder due to mutations at chromosome 22q12. The involvement of the brain
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Figs 19.4A and B: (A) Sagittal T1-weighted, MRI of a 26-year-old patient with NF1. (B) Asymmetrical optic chiasm glioma known for 12 years
structures in NF1 and NF2 are quite different: While NF2 consistently affects the acoustic/vestibular nerve, this is never encountered in NF1. NF2 is not associated with optic pathway gliomas. • Diagnostic criteria for neurofibromatosis type 2. The following are diagnostic: 1. Bilateral vestibular schwannomas; or 2. A first-degree relative with NF2 (Figs 19.5A and B), and either a unilateral vestibular schwannoma or two of the following: meningioma (Figs 19.6A and B), schwannoma, glioma, neurofibroma, posterior subcapsular lens opacity, or cerebral calcification; or 3. Two of the following: unilateral vestibular schwannoma multiple meningiomas either schwannoma, glioma, neurofibroma, posterior subcapsular lens opacity, or cerebral calcification. INTRACRANIAL PATHOLOGY OF THE VISUAL PATHWAY Intrinsic Lesions, Glioma in Adults The term glioma stands for the corresponding three types of glial cells. The three major types of gliomas originate from: astrocytoma oligodendroglioma and ependymoma and the so-called mixed gliomas that contain two or more different cell types in varying proportions, most frequently primarily oligoastrocytoma (Okazaki 1989), whereas intraventricular choroid plexus papilloma and carcinoma are distinct from ependymoma (Kleihues and Cavanee 2000).
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Figs 19.5A to D: T1-weighted, contrast-enhanced MRI of newly diagnosed NF2 in a 14-year-old girl. MRI shows bilateral acoustic neuromas, meningioma at tip of left temporal lobe, mass (presumably a meningioma) in suprasellar/left parasellar/ sphenoid area
Figs 19.6A and B: (A) Axial plain CT, (B) axial CT following administration of contrast medium in a 14-year-old-patient prompted by new onset of diplopia. Plain CT reveals calcifying right optic nerve sheath meningioma. Following contrast: left frontal meningioma
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Extra-axial Tumors Due to the fact that extrinsic (or extra-axial) tumors are frequently benign, the treatment and prognosis are based upon the correct diagnosis of suspected intracranial extrinsic masses. The use of MRI is mandatory for these tumors because it has the ability to differentiate the boundary between the brain parenchyma and the mass itself. The superior contrast resolution and multiplanar imaging capacity of MRI enable the identification of anatomic markers as cardinal features of an extra-axial lesion. Instead of the demonstration of the tissue contrast of extrinsic masses and brain parenchyma, the definition of boundary layers between the tumor and the brain surface permits the diagnosis of an extra-parenchymal intracranial lesion. The boundary layers represent cerebrospinal fluid (CSF), pial blood vessels, and/or the dura. CSF clefts are recognized as crescentic bands, frequently only over a portion of the tumor, with signal intensities similar to those of spinal fluid: low on T1-weighted, isointense on proton densityweighted, and high on T2-weighted images. In SE sequences, both normal anatomic and pathologic vessels are identified as rounded or curvilinear signal voids at specific locations of the lesion margin. The use of i.v. contrast agents enables the demonstration of the compartmentalization of extrinsic lesions, since a large number of tumors show a specific pattern, including extensive signal enhancement (meningioma, metastasis), while others show none (epidermoid and dermoid tumors) (Goldberg et al. 1996). Metastasis Intracranial metastasis or secondary brain tumors are defined as tumors involving the CNS and originate from, but are discontinuous with, primary systemic neoplasms. They account for 15 to 30 percent of all intracranial tumors in pathologic series (Okazaki 1989; Nelson et al. 2000). The most frequent primary malignancies include lung carcinoma (40% metastasize to the brain), breast carcinoma (roughly 25 percent metastasize to the brain) (Figs 19.7 and 19.8), hypernephroma, melanoma, and neuroblastoma, the latter occurring predominantly in children. All areas of the brain may be affected, with preference for the corticomedullary junction as the starting point (Okazaki 1989), possibly due to greater capillarization of this region (Zülch 1986). The sellar region is the preferred location for hematogenous spread of primary carcinoma of extracranial origin. In addition to the convexity of the brain and/or cerebellum, leptomeningeal tumor cells deposit in the recess of the third ventricle but may also invade the parenchyma of the hypothalamus and/or chiasm.
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Fig. 19.7: A 35-year-old woman with acute vision loss, predominantly of the right eye, and a history of breast carcinoma. Diagnosis: intra- and suprasellar metastasis. MRI: Axial T2-weighted FLAIR sequence showing edema of the chiasm and both optic tracts
Figs 19.8A to D: A 38-year-old-woman with chiasm syndrome, diabetes insipidus, and a history of breast carcinoma. Diagnosis: hypothalamic and chiasmal metastasis of breast carcinoma. T1-weighted MRI: (A) Axial native view showing a slightly hypointense lesion dorsal to the chiasm with apparent invasion. (B) Corresponding contrast-enhanced view, identifying invasion of the chiasm and the proximal optic tracts. (C) Coronal native view. (D) Midsagittal contrastenhanced view, demonstrating metastatic spread throughout the hypothalamus and pituitary stalk (D with permission of Müller-Forell 2001)
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SELLAR TUMORS Corresponding to the various tissues, a number of pathologic processes may occur. More than 30 different pathologic entities, primarily extrinsic lesions, involving and affecting structures of the sellar and juxtasellar region have been described (Osborn and Rauschning 1994). These tumors involve the brain parenchyma secondarily and are often cured completely without recurrences even if the lesion has reached a considerable size. Intrinsic brain tumors, which often show a recurrent clinical course even for benign tumors, develop less frequently in the sellar region. Gliomas of the Chiasm Gliomas of the anterior visual pathway, histologically defined as pilocytic astrocytoma are uncommon lesions, but account for approximately 65 percent of intrinsic tumors of the optic nerve. These lesions most frequently occur in children in the first decade of life (Dutton 1994), whereas only 10 percent present in patients older than 20 years (Wulc et al. 1989). As most of these gliomas are located in the intraorbital and intracranial part of the optic nerve (Fig. 19.9), additional involvement of the chiasm is seen in about 75 percent of patients However, only 7 percent occur in the chiasm itself, and 46 percent involve both the chiasm and hypothalamus the latter increasing the mortality rate to over 50 percent, since no specific therapy alters the final outcome (Dutton 1994). They are not associated with NF 1 and uniformly show a fatal course of usually less than 1 year (Rush et al. 1982; Mason and Kandal 1991; Dutton 1994; Hollander et al. 1999). Imaging Characteristics: MRI as the method of choice relaxation times. In macroadenomas, MRI enables a high anatomic resolution and definition of the neighboring tissue, i.e. intracranial optic nerves, chiasm, and cavernous sinus. In most cases, native, non-contrastenhanced images allow accurate and conclusive differentiation of the tumor and deformed, compressed, flattened visual structures of the optic of the pre- and post-contrast images does not routinely enable the definite prediction of tumor invasion of the cavernous sinus. Only a carotid artery encasement or an extension lateral of the cavernous sinus towards the temporal lobe is a reliable indicator of cavernous sinus invasion.
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Figs 19.9A to F: MRI: (A) Axial T2-weighted view with a very large, space-occupying, isointense lesion located in a widened suprasellar cistern, depressing and spreading the basal vessels, (B) Coronal T1-weighted native view demonstrating pressure exertion on the widened third ventricle by the central hypointense (necrotic) tumor, (C) Midsagittal, T1-weighted, contrast-enhanced view with demarcation of the entire enhancing tumor, compressing and displacing the brainstem, and extending into the posterior fossa. Note widening of the entrance of the otherwise normally configured sella (arrow), (D) Coronal native view with intra- and suprasellar lesion and inferior chiasmal compression. Note the slightly hypointense signal in the sphenoid sinus, (E) Corresponding contrast-enhanced view with inhomogeneous contrast enhancement of the intra-/suprasellar, apparently encapsulated lesion, but homogeneous enhancement in the sphenoid sinus. CORR = Sponding to sinus inflammation, note the small leptomeningeal enhancement at the base of the left frontal lobe (arrow), (F) Axial contrast-enhanced view with necrotizing, encapsulated tumor and leptomeningeal enhancement of the basal frontal sulci (arrows)
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Meningiomas Meningiomas (Fig. 19.10) associated with hereditary tumor syndrome such as schwannoma (i.e., in patients with NF2) (Woodruff et al. 2000) mainly occur in younger patients. Approximately 20 percent of meningiomas are located in the sellar region, with 50 percent arising from midline structures such as the sphenoid plane tuberculum sellae diaphragm sellae, or the dura of the cavernous sinus Globular meningiomas of the suprasellar or paraclinoid region may produce early ophthalmological symptoms because of optic nerve.
Figs 19.10A to C: MRI: (A) Axial view in the region of the chiasm, visualizing the superior region of the right sphenoid wing meningioma and an ipsilateral temporal meningioma. Note the susceptibility artifacts after left temporal craniotomy. (B) Coronal view at the cavernous sinus, showing the entire circumference of the meningioma of the right anterior clinoid process. Note the left temporobasal parenchyma defect after initial surgery. (C) Coronal view in the region of the chiasm with tumor extension to the right chiasmal region. Another frontal meningioma is demarcated in addition to the known temporal meningioma or chiasmal compression and therefore do not normally exceed 2 cm in diameter
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Imaging Characteristics: Due to their high cell density and psammomatous calcification, meningiomas of the sellar region present on CT as isodense to hyperdense midline lesions. Diffuse hyperostosis is particularly apparent on CT images of en plaque meningioma). A perifocal edema is detected only in the rare cases where the cerebral cortex is destroyed by this tumor Apart from the differentiation of pituitary adenomas, where a trans-sphenoidal approach is the preferred operative procedure, the most important question for neurosurgeons is the possible invasion of the cavernous sinus and/or narrowing of the ICA, which is best addressed by MRI. Craniopharyngioma They are assumed to arise from Rathke’s pouch epithelium and account for 1.2-4.6 percent of all intracranial tumors and thus represent the second most frequent tumors of the sellar region after pituitary adenomas. Craniopharyngiomas (Figs 19.11A to D) show no sex bias but a bimodal age distribution, with one peak involving children and adolescents and another one involving adults (Adamson et al. 1990; Crotty et al. 1995). A clinicopathologic distinction is made between adamantinous and papillary craniopharyngioma. Most adamantinomas are hormone-inactive lesions and present as solid tumors with a variable, at times predominantly cystic component, containing cholesterol-rich, thick, brownish-yellow fluid with the appearance of machine oil. Imaging Characteristics: CT in the axial and coronal views is still justified for the basic and differential diagnosis of craniopharyngiomas, in view of the characteristic calcification of parts of the tumor seen in 50-70% of cases Even in the absence of calcification, the solid tumor parts appear hyperdense with prominent contrast enhancement, whereas the cysts seem isodense to CSF and may show enhancement of the wall MRI enables superior delineation of the tumor extent, especially on the coronal and sagittal views Morphology and signal patterns are marked by great variety: adamantinous craniopharyngioma primarily shows a combination of T1-weighted hypoin-tense and T2-weighted massive hyperintense signal character, (whereas in papillary craniopharyngioma, a hyperintense signal on T1-weighted and hypointensities on T2-weighted sequences may dominate. The solid tumor parts of both types generally show a hyperintense signal on T1-weighted images and prominent enhancement of the tumor and cyst wall).
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Figs 19.11A to D: (A) Coronal, T1-weighted, contrast-enhanced image with caudal depression of the third ventricle by the predominantly suprasellar, cystic tumor. The contrast-enhanced capsule is visualized, while the chiasm is not seen. (B) Midsagittal view with differentiation of the pituitary stalk (star). Note the depression, dislocation, and deformation of the brainstem. (C) Axial T2-weighted image demonstrating the high proton content (high signal) of the oily fluid content of the cystic tumor region. Note the deformed brainstem. (D) Corresponding T1weighted, contrast-enhanced image where a remnant of the chiasm (confirmed on operation) is seen at the medial right tumor surface (arrow)
Astrocytomas Astrocytic tumors, represent the most frequent entity of primary brain tumors with up to 60 percent of all intracranial neoplasms and comprise a wide range of age and gender distribution, growth potential, extent of invasiveness, morphological features, tendency for progression, and clinical course (Okazaki 1989; Cavanee et al. 2000). Astrocytomas primarily manifest in adults and may arise at any site of the CNS, exhibiting a wide range of histopathological features and
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biological behavior. Astrocytomas include, e.g. pilocytic and subependymal giant cell astrocytoma (both WHO I), diffuse low grade astrocytoma (WHO II), anaplastic astrocytoma (WHO III), and glioblastoma (WHO IV). These different entities reflect the type and sequences of genetic alterations acquired during the process of transformation, where the progression from low grade to anaplastic astrocytomas and glioblastomas is associated with the cumulative acquisition of multiple genetic alterations (Cavanee et al. 2000). Pilocytic Astrocytoma (WHO I) Pilocytic astrocytomas (WHO I) should be differentiated from diffuse growing astrocytomas as they are more circumscribed, slow-growing lesions with different location, morphology, genetic profile, and clinical behavior. High Grade Glioma Diffuse astrocytoma (WHO II) is characterized by a high degree of cellular differentiation, slow growth, and diffuse infiltration of the adjacent brain structures. It has a tendency for malignant progression to anaplastic astrocytoma and, ultimately, glioblastoma). Most of these patients are adults (presenting with seizures and clinical symptoms, depending on the localization. Imaging Characteristic: Although most glial tumors arise from a segment of only one gyrus (Yasargil 1994), the affected parenchyma (usually white matter, but an involvement of gray matter is often seen) demarcates an ill-defined area, hypodense on CT. On MRI, astrocytomas mostly present as mildly hypointense on T1-weighted and hyperintense on T2-weighted, due to the fact that they represent a degenerative microcystic formation, filled with clear fluid, and an irregular, not always clearly distinguished perifocal edema. Metastasis Secondary lesions should always be included in differential diagnostic considerations of extrinsic and even intrinsic tumors of the sellar region, particularly with a view to the capacity of some primarily extracranial tumors to involve the skull base (percontinuitatem) or be hematogenous. Metastases involving the cavernous sinus predominantly arise from malignant tumors of the nasal cavity, growing perineurally or perivascularly via the basal foramina.
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Imaging characteristics are nonspecific and similar to those encountered in more common tumors of the sellar region. Cavernoma (Syn. Cavernous Hemangioma) of the Cavernous Sinus They present as well-defined tumorous lesions with a homogeneous, intermediate signal on T1-weighted views, a hyperintense signal on T2-weighted sequences, and homogeneous, massive enhancement after gadolinium administration. The Tolosa-Hunt syndrome The Tolosa-Hunt syndrome (THS) is an inflammatory disease of unknown origin, limited to the superior orbital fissure and the cavernous sinus (Smith and Taxdal 1966). The presentation of cranial nerve paresis of one or several of the cranial nerves passing the cavernous sinus (N III, N IV, N VI, and N V1) may coincide with the onset of orbital pain or follow it within a period of up to 2 weeks. The pain must be relieved within 72 hours after steroid therapy. Although high resolution CT or MRI can neither exclude nor confirm THS when a lesion compatible with an inflammatory process is visualized, other causative lesions as, e.g. a malignant tumor must be excluded. Clinical and neuroradiological follow-up must be done for at least 2 years, even in patients with negative findings on imaging at onset. Cystic Lesions In the differential diagnosis of suprasellar tumorlike lesions, arachnoid cyst and epidermoid cyst play some important role, along with Rathke’s cleft cyst and hypothalamic hamartoma. Rathke’s cleft cyst, a benign epithelium-lined cyst arising from remnants of Rathke’s pouch, may become symptomatic in the case of intra-and suprasellar extension, a rather rare condition (Rose et al. 1992). On MRI, signal intensities vary with cyst content from serous to mucoid (Osborn 1994b). Arachnoid cysts account for about only 1 percent of all intracranial space-occupying lesions, but 10 percent arise in the suprasellar region (Armstrong et al. 1983). Arachnoidal cysts are filled with CSF; the etiology of these mainly congenital lesions remains poorly understood and controversial, but meningeal mal-development is preferred, so that minor aberrations of CSF flow through the loose, primitive, perimedullary mesenchyme are considered to result in a focal splitting of leptomeninges and the formation of a diverticulum or blind pocket
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within the arachnoid membrane (Schachenmayr and Friede 1979; Becker et al. 1991). As an arachnoid cyst is a well-defined, sharply demarcated, extra-axial formation filled with CSF, MRI signal characteristics correspond with hypointense signal on T1-weighted and hyper-intensity on T2-weighted images. Epidermoid cysts probably arise from inclusion of ectodermal epithelial elements at the time of neural tube closure (accounting for 0.2–1% of all primary intracranial tumors, 7 percent of them in the suprasellar region (Osb or n 1994b). Imaging of these well-delineated, tumor-like cystic lesions is not always able to differentiate them from arachnoid cyst, especially since the MRI signal intensities are similar to CSF in every conventional sequence. DWI confirms the diagnosis. Multiple Sclerosis The onset of MS usually occurs in patients aged from 20 to 40 years (15% before 20 years of age, 10 percent after 50 years) with a female predominance. Most often, the first and only clinical symptom consists of impaired vision, presenting as retrobulbar neuritis (RBN), followed or combined with fluctuating periods of sensomotoric or gait disturbances. The clinical course of disease progression can be divided into a relapsing-remitting and a chronic progressive form (Heaton et al. 1985). For the diagnosis of MS recently published new guidelines on diagnostic criteria of MS enable the physician to define the diagnosis for MS, possible MS or nor MS, replacing the diagnostic criteria of Poser et al from 1983 (McDonald et al. 2001). These guidelines include the evidence of dissemination in time and space of lesions typical for MS, objectively determined with clinical and imaging signs. The obtained imaging criteria for MS should require evidence of at least three of the four following findings: 1. One gadolinium enhancing lesion or nine T2-hyperintense lesions if there is no gadolinium enhancing lesion, 2. At least one infratentorial lesion, 3. At least one juxtacortical lesion, 4. At least three periventricular lesions. Additional fi ndings of CSF abnormalities with the presence of autochtone IgG production (oligoclonal bands) (McLean et al. 1990), lymphocytic pleocytosis, and abnormal VEP, typical for MS (delayed but with well preserved wave form) provide supplement information (Halliday 1993) to clinical finding of neurological disturbances typical for MS. Imaging Characteristics: MRI is the imaging tool of choice in suspected demyelinating disorders (Sartor 1992; Osborn 1994f; vander Knaap
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and Valk 1995a; Edwards-Brown and Bonin 1996; McDonald et al. 2001). Although the sensitivity in detecting MS lesions is about 85 percent (Lee et al. 1991), the correlation of neurological symptoms and localization of imaging findings is generally poor as most foci are clinically silent (Barkhof et al. 1992), but in some cases a correlation of clinical and imaging findings is probable The imaging protocol should include axial and sagittal PD/T2-weighted and FLAIR sequences, where the demyelinated areas demonstrate a high signal (Filippi et al. 1999a; Reiche et al. 2000). The sagittal view is best in order to show the characteristic periventricular/ pericallosal, ovoid lesions (so-called Dawson’s finger), caused by the centripetal course of the medullary veins, representing the perivascular inflammation (Horowitz et al. 1989). T1-weighted native and contrast-enhanced sequences demonstrate acute or recurrent inflammatory lesions, which normally enhance contrast media, caused by BBB disruption (Paty 1997; Fazekas et al. 1999; Reiche et al. 2000). involvement including the optic chiasm and nerves is the most common site of affection (Mirfakhraee et al. 1986; Okazaki 1989). Depending on the character of the lesions (solitary, multiple, or diffuse disseminating), imaging findings may resemble multiple sclerosis, systemic lupus erythematosus (SLE), non-Hodgkin lymphoma (NHL) or even inflammatory affections like tuberculous menengitis) (Edwards-Brown and Bonin 1996; Woitalla et al. 2000). As periventricular signal intense lesions are seen in about 50 percent of the patients, the differential diagnosis from multiple sclerosis may be difficult, but a possible additional leptomeningeal involvement makes the diagnosis of sarcoidosis more likely (Hayes et al. 1987; Zajicek et al. 1999; Woitalla et al. 2000). In solitary or multiple lesions which often demonstrate a contrast enhancement and show a preference for the diencephalon (the floor of the third ventricle, hypothalamus) and suprasellar region, solid tumors of the suprasellar region should be taken into consideration in the differential diagnosis, along with multiple metastasis, NHL, or Langerhans’ cell histiocytosis 67 percent of patients with sarcoidosis, leptomeningeal and/or ependymal involvement is found. Toxoplasmosis Corresponding to pathological changes, a “target” appearance of the solitary or multiple ringenhancing masses with perifocal edema is common. Rim or focal nodular enhancement following contrast administration are seen on CT and also on MRI. The most important,
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but sometimes hardly distinguishable differential diagnosis is from primary CNS lymphoma (Dina 1991). While a periventricular location and subependymal spread favor lymphoma, more than one lesion, preferentially adjacent to or in the region of the basal ganglia, make toxoplasmosis likely (Osborn 1994g). Acute Disseminated Encephalomyelitis (ADEM) In contrary to multiple sclerosis, ADEM is characterized by an acute monophasic disorder, predominantly occurring following a viral infection or vaccination with a mean latent period of 4-6 days or several weeks; sometimes it is seen without recognized antecedent. ADEM may occur at any age, but shows a preference for children or young adults (Consequently, the simultaneous occurrence of polytopic neurological symptoms such as hemi-, di- or tetraplegia, cerebellar ataxia or cranial nerve palsies, combined with optic neuritis and bladder dysfunction, may lead to the correct diagnosis. As in all demyelinating diseases, MRI shows best the mainly subcortical, confluent, bilateral but slightly asymmetric hyperintense foci on T2-weighted images. Consequently, along with the monophasic clinical symptoms, if BBB disruption is apparent, a similar enhancement of the lesion is seen, in contrast to MS, where only acute foci show a T1 time shortening with signal enhancement. BIBLIOGRAPHY 1. Aicardi J. Diseases of the nervous system in childhood, (2nd edn) MacKeith, Leeds 1998. 2. Albermaz VS, Castillo M, Hudgins PA, Mukherji SK. Imaging findings in patients with clinical anopththalmos. AJNR Am J Neuroradiol 1997;18:555–61. 3. Alsnall E, Rutka JT, Becker LE, Hoffman HJ. Optic chiasmatic-hypothalamic glioma. Brain Pathol 1997;7:799–806. 4. Arnoldi KA, Tychsen L. Prevalence of intracranial lesions in children initially diagnosed with disconjugate nystagmus (spasmus nutans). J Pediatr Ophthalmol Strabismus 1995;32:296–301. 5. Atkinson J. Human visual development over the first 6 months of life. A review and a hypothesis. Hum Neurobiol 1984;3:61–74. 6. Bajaj SK, Kurlemann G, Schuierer G, Peters PE. CT and MRI in a girl with lateonset ornithine transcarbamylase deficiency: case report. Neuroradiology 1996;38:796–9. 7. Barkovich AJ. Pediatric neuroimaging, (2nd edn). Raven, New York 1995. 8. Krenning EP, Kwekkeboom DJ, Bakker WH, Breeman WA, Kiji PP, Oei HY, van Hagen M, Postema PT, de Jong M, Reubi JC. Somatostatin receptor scintigraphy with (111-INDTPA-D Phe 1)- and (1231– Tyr3)-octreotide: the Rotterdam experience with more than 1000 patients. Eur J Nucl Med 1993;20: 716–31.
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9. Kueker W, Ramaekers V. Persistent hyperplastic primary vitreous: MRI. Neuroradiology 1999;41:520–22 10. Kupersmith MJ. Neurovascular neuroophthalmology. Springer, Berlin Heidelberg New York 1993. 11. Kuroiwa T, Ohta T, Tsutsumi A. Xanthoma of the temporal bone: case report Neurosurgery 2000;46:996–8. 12. Kyritsis AP, Tsokos M, Triche TJ, Chader GJ. Retinoblastoma: origin from a primitive neuroectodermal cell? Nature 1984;307:471–3. 13. Lagreze WD, Wesenthal TA, Kommerell G. Enophthalmus durch orbitale metastase eines Mammkarzinoms. Klin Monatsbi Augenheilkd 1997;211:68–9. 14. Lake B. Lysosomal and peroxisomal disorders. In: Graham D, Lantos PL (eds) Greenfield’s pathology. Arnold, London, 1997;657–753. 15. Osborn A. Infections of the brain and its linings. In: Osborn A (ed) Diagnostic neuroradiology. Mosby, St Louis, 1994;673–715. 16. Osborn A. Diagnostic cerebral angiography, (2nd edn). Lippincott/Williams and Wilkins, Philadelphia 1999. 17. Osborn A, Rausching W. Brain tumors and tumor like masses: classification and differential diagnosis. In: 1994. 18. Osborn A (Ed). Diagnostic neuroradiology. Mosby, St Louis, 401–528. 19. Patel U, Gupta SC. Wyburn-Mason syndrome. A case report and review of the literature. Neuroradiology 1990;31:544–6. 20. Paty DW. MRI as a method to reveal in vivo pathology in MS. J Neural Transm [Suppl] 1997;49:211–7. 21. Paulus W, Jellinger K, Morgello S, Deckert-Schlüter M. Malignant lymphomas. In: Kleihues P, Cavenee WK (Eds) pathology and genetics. Tumors of the nervous system. IARC, Lyon, 2000;198–203. 22. Perilongo G, Carollo C, Saviati L, Murgia A, Pillon M, Basso G, Gardiman M, Laverda AM. Diencephalic syndrome and disseminated juvenile pilocytic astrocytoma of the hypothalamic-optic chiasm region. Cancer 1997;80:142-6. 23. Schwab SJ, Hlatky MA, Pieper KS, Davidson CJ, Moris KG, Skelton TN, Bashore TM. Contrast nephrotoxicity: a randomized controlled trial of a nonionic and an ionic radiographic contrast agent. N Engl J Med 1989;320:149–53. 24. Tamraz J. Neuroradiologic investigation of the visual system using magnetic resonance imaging. J clin neurophysiol 1994;11:500–18. 25. Trommer G, Koesling S, Nerkelun S, Gosch D, Kloppel R. Darstellbarkeit von Orbita-Fremdkörpern in der CT. 1st die Fremdkörperübersicht noch sinnvoll? Fortschr Röntgenstr 1997;166:487–92. 26. Uder M. Nierenschädigung durch jodhaltige Röntgenkontrastmittel. Urologe 1998;37:530–31. 27. Wangemann BU, Jantzen JP, Dick W. Anaesthesiologische Asoekte allergischer Reaktionen am Beispiel des “Kontrastmittelzwischenfalls”. Anaesthesiol intensivmed 1988;29:205–14. 28. Weetman AP, Wiersinga WM. Current management of thyroid-associated ophthalmopathy. Results of an international study. Clin Endocrinol (Oxf) 1998;49:21–28. 29. Wichmann W, von Ammon K, Fink U, Weik T, Yasargil GM. Aneurysm clips made of titanium: agnetic characteristics and artifacts in MR. AJNR Am J Neuroradiol 1997;18:939–44.
Index Abducent nerve 132 clinical features deviation 135 diplopia 135 head posture 135 ocular movements 135 course 132 cavernous sinus 134 orbit 134 superior orbital fissure 134 exit from the brain 132 lesions 136 nucleus 132 Aberrant regeneration of oculomotor nerve 121 Acute disseminated encephalomyelitis 236, 251 Adrenaline test 67 Alexander’s law 34 Amaurotic pupil 60 Anatomy of the supranuclear pathways 1 Anophthalmos 223 Aplasia 151 Argyll Robertson pupil 63 Astrocytomas 246
Carotid-cavernous fistula 216 Cavernoma 248 Cavernous sinus syndrome 121, 126, 137 Central Horner’s syndrome 67 Cerebellar disorder 30 Cerebellopontine angle tumor 147 Chronic progressive external ophthalmoplegia 200 Ciliary ganglion 114, 115 Claude’s syndrome 120 Cocaine test 67 Coloboma of optic disk 153 Computed tomography 226 contrast medium 227 principles 226 Conjugated palsies 18 lesions of the basal ganglia overactivity 22 underactivity 22 lesions of the collicular area 22 lesions of the frontal cortex 18 bilateral underactivity 21 overactivity 18 unilateral underactivity 20 Craniopharyngioma 205, 245 Cuneus 83 Cystic lesions 248
B
D
Bell’s palsy 149 Benedict’s syndrome 119 Bergmister’s papillae 152 Behr syndrome 186 Bielschowsky’s head tilting test 127 Blepharospasm 201 Botulinum toxin injection 139 Brainstem syndrome 136 Breughel syndrome 202
Darkness reflex 59 Diplopia 126, 135 Dissociated palsies 23 vertical 27 Doll’s head phenomenon 50
A
C Calcarine sulcus 82 Caloric test 43
E Enophthalmos 66 Examination of a neuroophthalmology case 219 direct light reflex 220 examination 219
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indirect light reflex 220 near reflex 221 CNS examination 225 confrontation visual fields 221 diplopia charting 222 fundus examination 223 Hess charting 222 nystagmus 223 ocular movements 221 other cranial nerve examination 224 reflexes 225 visual fields 223 past history 219 pupil examination 220 swinging flash light test 220 testing of color vision 220
F Facial anhydrosis 67 Facial myokymia 203 Facial nerve course 145 lesions 147 nucleus 145 Foster Kennedy syndrome 192 Foville’s syndrome 137 Functional visual loss 211
G Geniculate ganglionitis 148 Gliomas 157 of the chiasm 242 high grade 247 Gradenigo’s syndrome 137
H Headache 206 Hemifacial spasm 202 Hess charting 222 Heterochromia iridis 67 Hippus 71 Horner’s syndrome 66 Hummelsheim’s operation 139 Hutchinson’s pupil 65, 120 Hydroxyamphetamine test 67
Hyperdeviation 126 Hypoplasia 151
I Intermediary tissue of Kuhnt 107 International Headache Society 208 Internuclear ophthalmoplagia 4, 23 classification 24 etiology 24 Intracranial aneurysms 214 Intracranial pathology 238 extra-axial tumors 240 glioma 238 metastasis 240 Ischemic optic neuropathy 193 arteritic anterior classic signs 193 differential diagnosis 194 etiology 193 management 195 symptoms 194 posterior 195 Isolated fourth nerve palsy 126 Isolated ipsilateral tear deficiency 149 Isolated sixth nerve palsy 138
J Jensen operation 139 Juvenile pilocytic astrocytoma 157
K Kearns-Sayre syndrome 200 Kjer syndrome 186
L Lateral geniculate bodies 79, 87 Lesions of visual pathways 93 lateral geniculate body lesions 98 optic nerve type field defect 93 arcuate nerve fiber bundle 94 bitemporal hemianopia 96 central bitemporal hemianopia 96 junctional scotoma 96 lower temoporal quantrantic defects 98
Index nasal nerve fiber bundle defects 95 papillomacular bundle 93 upper temporal quadrantic defects 97 optic radiations and visual cortex lesion 99 occipital lobe lesion 100 parietal lobe lesions 100 temporal lobe lesions 99 Lid apraxia 203 Light-near dissociation 64
M Macular fibers 87 Magnetic resonance imaging 228 claustrophobia, sedation, surveillance 232 optic pathway pathology 232 restrictions 231 Malignant gliomas of the optic nerve 169 clinical features 169 pathology 170 prognosis 170 radiology 170 Marcus gunn pupil 61 Meige’s syndrome 202 Meningiomas 244 Metastasis 247 Meyer’s loop 81 Micronystagmus 34 Micro-ophthalmos 233 Migraine 206 Millard-Gubler syndrome 136 Miosis 66 Morning glory syndrome 155 Multiple sclerosis 236, 249 Myelineated nerve fibers 152 Myotonic dystrophy 201
N Nasal fibers 86 Neurofibromatosis 237 Non-optic reflex system disorders 30 Nothnagel’s syndrome 119 Nuclear fascicular syndrome 125
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Nuclear third nerve paresis 118 Nystagmus 32 central 51 cerebellar 51 deviational 36 hysterical 51 idiopathic congenital 52 jerky 34 neutral zone 34 null zone 34 nystagmus blockage syndrome 52 ocular 35 optokinetic 36-38 pathological ocular amaurotic 41 amblyopic 41 latent 41 Miner’s 41 spasmus nutans 41 pendular 33 rotational 48 vertical vestibular 45 canal paresis 46 directional preponderance 47 vestibular 43 voluntary 51
O Ocular myasthenia clinical features 197 investigations 198 electromyography 199 neostigmine test 198 tensilon test 198 treatment 199 medical 200 optical 19 surgical 200 Ocular tumors 233 Oculomotor (third cranial) 109 blood supply 117 branches 116 cavernous sinus 112 ciliary ganglion 114 course in superior orbital fissure 112 course in the orbit 114 exit from the brain 110 nucleus 109
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One and one-half syndrome 26 Optic atrophy 185 clinical features 186 differential diagnosis 187 Optic chiasma 75 Optic disk pit 156 Optic nerve 85, 103 blood supply intracanalicular 107 intracranial 107 intraocular 108 intraorbital 108 course intracanalicular 103 intracranial 103 intraocular 104 intraorbital 104 relations intracanalicular 104 intracranial 104 intraocular 105 intraorbital 104 Optic nerve gliomas 157 association with neurofibromatosis 160 clinical features 158 histopathology 162 management 167 microscopic findings 164 presenting signs and symptoms 159 radiographic findings 161 Optic nerve head drusen 152 Optic nerve hypoplasia 235 Optic nerve meningiomas 170 clinical features 171 histopathology 174 management 178 radiology 173 signs and symptoms 171 Optic neuritis 187 clinical features 188 management 189 optic neuritis treatment trial 189 Optic radiation 81, 88 Optic tract 87 Optokinetic nystagmus drum 36 Orbital syndrome 121, 126, 138
P Papilledema 190 clinical features 190 management 193 Paradoxical papillary reaction 71 Paralytic pontine exotropia 26 Parinaud’s syndrome 22 Partial ipsilateral facial palsy 149 Periventricular leukomalacia 236 Petrous apex syndrome 137 Pharmacology of the pupil 68 Phenylephrine test 67 Pilocytic astrocytoma 247 Pituitary tumors 204 Polycoria 72 Posterior communicating artery aneurysm 120 Pseudo-Ishihara’s chart 220 Pseudo-Argyll Robertson pupil 64 Pseudo-Gradenigo’s syndrome 137 Pseudo-ophthalmoplegia 17 Psychosensory reflex 60 Ptosis 66 Pupil abnormalities 71 Pupil cycle time 60 Pupil gaze dyskinesis 121 Pupillary pathways 54 accommodation reflex pathway 57 convergence near reflex pathway 56 papillary dilatation pathway 58 pupulloconstrictor light reflex pathway 54 Pupil-sparing isolated third nerve paresis 121 Pursuit disorders 29
R Raymond’s syndrome 136 Reader’s syndrome 68 Retinoblastoma 233 Retinochoroidal coloboma 153
S Saccadic disorders 17 Secondary optic nerve tumors 179
Index blood-borne metastasis 180 extension from adjacent structures 181 extension from the eye 179 extension from the meninges and brain 181 Sellar tumors 242 Septo-optic dysplasia 234 Spasmus nutans 233 Subarachnoid hemorrhage 214 Subarachnoid space syndrome 126, 137 Superior orbital fissure 112, 113, 124 Supranuclear eye movement systems 2 non-optic reflex system 12 position maintenance system 15 pursuit system 6 saccadic system 2 vergence system 11 Supranuclear lesion 147 Swinging flash light test 61, 220
T Tardive dyskinesia 203 Terson’s syndrome 214 Third nerve fascicle syndromes 119 Tic douloureux 203 Tilted disk 155 Tolosa-Hunt syndrome 248 Tonic pupil 64 Tourette’s syndrome 202 Toxoplasmosis 250 Trauma (nonaccidental injury) 236 Trigeminal nerve exit from the brain 140 mandibular division 143 maxillary division 143 nucleus 140 ophthalmic division 141 frontal nerve 142 lacrimal nerve 142 nasocilliary nerve 142 trigeminal cave 140 Trochlear nerve 123 course cavernous sinus 124 exit from the brain 123
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exit from the nucleus 123 orbital course 124 superior orbital fissure 124 lesions 125 nucleus 123
U Uncal herniation syndrome 120
V Vergence disorders 29 Vestibular system disorders 30 Visual cortex 83, 88 Visual pathways 73 blood supply 89 lateral geniculate body 92 optic chiasma 91 optic nerve 90 optic radiations 92 optic tract 91 retina 90 visual cortex 92 lesions 93 level 73 lateral geniculate body 79 optic chiasma 75 optic nerve 73 optic radiations 81 optic tract 77 retina 73 visual cortex 82 localization 84 lateral geniculate body 87 optic chiasma 86 optic nerve 85 optic radiation 88 optic tract 87 retina 84 visual cortex 88
W Weber’s syndrome 120 Wernicke’s hemianopic pupil 63 Wolfram syndrome 186
