Manual of

Neuro-ophthalmology

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Jitendar P Vij

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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.

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First Edition: 2009

ISBN 978-81-8448-411-3

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Printed at Ajanta

This book is dedicated to a lovely couple

Marguerite Mcdonald and Stephen Klyce

viii 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

Supranuclear 1 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.

2 Manual of Neuro-ophthalmology

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

4 Manual of Neuro-ophthalmology

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

Supranuclear Pathways for Eye Movements 5

Fig. 1.3: Vertical saccade pathway

LELeft eye; RERight eye; Occ.LobeOccipital Lobe; IIIIII Cranial nerve nucleus; VIVI Cranial nerve nucleus; PGCPontine gaze center; MLFMedial longitudinal fasciculus; UMN PathwayUpper motor neuron pathway; LMN PathwayLower 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.

Supranuclear Pathways for Eye Movements 7

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

Supranuclear Pathways for Eye Movements 11

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.

12 Manual of Neuro-ophthalmology

Fig. 1.8: Voluntary vergence pathway

LRLateral rectus; MRMedial rectus; LELeft eye; RERight eye; Occ.LobeOccipital Lobe; Fron.lobeFrontal lobe; IIIIII Cranial nerve nucleus; VIVI Cranial nerve nucleus; PGCPontine gaze center; MLFMedial longitudinal fasciculus; UMN PathwayUpper motor neuron pathway; LMN PathwayLower 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.

Supranuclear Pathways for Eye Movements 13

Fig. 1.9: Pursuit or reflex vergence pathway

LRLateral rectus; MRMedial rectus; LELeft eye; RERight eye; IIIIII Cranial nerve nucleus; VIVI Cranial nerve nucleus; PGCPontine gaze center; MLFMedial longitudinal fasciculus; UMN PathwayUpper motor neuron pathway; LMN PathwayLower 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

14 Manual of Neuro-ophthalmology

Fig. 1.10: Non-optic reflex system pathway

LRLateral rectus; MRMedial rectus; LELeft eye; RERight eye; IIIIII Cranial nerve nucleus; VIVI Cranial nerve nucleus; PGCPontine gaze center; MLFMedial longitudinal fasciculus; VNVestibular nucleus; UMN PathwayUpper motor neuron pathway; LMN PathwayLower 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

Supranuclear Pathways for Eye Movements 15

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

16 Manual of Neuro-ophthalmology

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.

Supranuclear

2 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.

18 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).

20 Manual of Neuro-ophthalmology

Fig. 2.2: Frontal adversive attack

Occ.LobeOccipital Lobe; Fron.lobeFrontal lobe; PGCPontine 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.

Supranuclear Disorders of Eye Movements 21

Fig. 2.3: Frontal lobe underactivity

Occ.LobeOccipital Lobe; Fron.LobeFrontal lobe; PGCPontine 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

22 Manual of Neuro-ophthalmology

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

Supranuclear Disorders of Eye Movements 23

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.

24 Manual of Neuro-ophthalmology

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

26 Manual of Neuro-ophthalmology

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

Supranuclear Disorders of Eye Movements 27

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,

Supranuclear Disorders of Eye Movements 29

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.

30 Manual of Neuro-ophthalmology

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

Supranuclear Disorders of Eye Movements 31

Fig. 2.10: Vestibular lesion

LRLateral rectus; MRMedial rectus; LELeft eye; RERight eye; Occ.LobeOccipital Lobe; Fron.lobeFrontal lobe; IIIIII Cranial nerve nucleus; VIVI Cranial nerve nucleus; PGCPontine gaze center; MLFMedial longitudinal fasciculus; VNVestibular 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.