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In afoveate animals, most visually-guided ocular motor behavior is little affected by removal of visual cortex. In primates, however, the situation is less clear. To further explore the ocular motor capabilities of “cortically blind” monkeys we studied optokinetic responses, vestibulo-ocular reflex (VOR) gain adaptation, and smooth pursuit tracking in three juvenile macaques before and after bilateral occipital lobectomies.

It has been suggested that the appearance of directional asymmetry and/or a reduced time constant of optokinetic afternystagmus (OKAN) might be a clinical index of vestibular imbalance. However, we do not know the limits for OKAN parameters in normal humans. Accordingly, we studied OKAN in 30 normal subjects using a "sampling" method, in which a number of values of OKAN are obtained by turning out the lights periodically during optokinetic stimulation. We found that the initial velocity of OKAN has a large intrasubject variability. Accordingly, if precision is desired so as to obtain 95% confidence that the measured mean of the initial velocity of OKAN is within 25% of the true mean in an individual subject, at least eight measurements of the initial OKAN velocity must be taken. When 12 measurements are made, all subjects had a minimum value of 5 degrees/s initial OKAN, and there was little directional asymmetry (mean of -0.47 degree/s +/- 3.13 degrees/s). The intrasubject variability of the time constant of OKAN was similar to the variability of initial OKAN velocity. However, because it is not possible to obtain repeated measures of the time constant in a short period of time, the time constant of OKAN is less likely to be useful in clinical testing.

Saccadic eye movements were measured in ten patients with unilateral limitation of function of an extraocular muscle. With the paretic eye fixating, there were a series of saccades when refixating in the direction opposite to the paralysis. Between each saccade, the eye drifted back toward the starting position; the drift rate decreased as the eye moved into the field of action of the strong agonist muscle. In one patient, the normal (covered) eye was immobilized during attempted refixations. In this case, the abnormal pattern of saccades made by the paretic eye persisted. Thus, the central nervous system uses innervation or efference to calculate the position of the eye in the orbit for saccadic eye movements.

The effect of tilt on the time constant of post-rotatory nystagmus was determined in a group of normal subjects and patients with cerebellar lesions. The normal subjects showed a vestibular response that decayed with a time constant of 19.6 s when upright and 7.2 s after tilt prone. Patients with midline cerebellar lesions near the uvula and nodulus had time constants that were normal in the upright position but were unaffected by head tilt. Patients with cerebellar lesions due to the Arnold-Chiari malformation showed behavior that was intermediate between that of normal subjects and the patients with midline lesions. These results provide evidence that in humans, the midline cerebellum regulates a neural network in the brainstem that perseverates peripheral vestibular input.

Alexander's law refers to the phenomenon in which the spontaneous nystagmus of a patient with a vestibular lesion is more intense when the patient looks in the quick-phase than in the slow-phase direction. Alexander's law was investigated in normal subjects as well as patients with vestibular lesions. During sinusoidal rotations of normal subjects, there was no trace of this phenomenon when subjects looked 25 degrees left and right in the dark. The phenomenon of Alexander's law is therefore created centrally and is not due to any mechanical properties of the orbit. During rotation at constant velocity in the dark, normal subjects did weakly demonstrate Alexander's law because of a mild gaze-evoked nystagmus present in normal subjects in the dark. Gaze-evoked nystagmus from a cerebellar lesion involved a pronounced demonstration of Alexander's law during rotatory nystagmus. In patients with a vestibular lesion and a mild spontaneous nystagmus in the dark that obeyed Alexander's law, the nystagmus reversed upon far gaze in the slow-phase direction. We propose that in patients with a vestibular lesion, the phenomenon of Alexander's law is created by the sum of vestibular nystagmus and an abnormally large gaze-evoked nystagmus that is consequent to the vestibular lesion. This conclusion has a number of neurological implications concerning the ways in which the nervous system attempts to compensate for vestibular lesions.

In certain patients with peripheral or central vestibular lesions, a transient nystagmus appears after shaking the head rapidly for 10 to 20 cycles. We recorded such a "head-shaking nystagmus" using the scleral eye coil in six subjects with unilateral peripheral vestibular lesions. Horizontal head shaking elicited horizontal nystagmus with slow phases that were initially directed toward the side of the lesion and upward. All subjects showed a prolonged, lower-amplitude reversal phase after the initial response following horizontal head shaking. The main features of these results can be explained by an analytic model that incorporates a central velocity-storage mechanism that perseverates vestibular inputs, Ewald's second law, and adaptation of primary vestibular afferent activity.

For the vestibulo-ocular reflex (VOR) to function properly, namely to ensure a stable retinal image under all circumstances, it should be able to take into account varying eye positions in the orbit and varying orientations of the head with respect to the axis about which it is rotating. We tested this capability by quantifying the gain and the time constant of the horizontal component of the VOR during rotation about an earth vertical axis when the line of sight (optical axis) was moved out of the plane of head rotation — either by rotating the eyes up or down in the orbit or by pitching the head up or down with respect to earth-horizontal. In either case the gain of the horizontal component of the VOR was attenuated precisely by the cosine of the angle made between the optical axis and the plane of head rotation. Furthermore, if the head was pitched up or down but the eye rotated oppositely in the orbit so as to keep the line of sight in the plane of head rotation the gain of the horizontal component of the VOR was the same value as with the head and eyes both straight ahead. In contrast, the time constant of the VOR varied only as a function of the orientation of the head and not as a function of eye position in the orbit. During rotation about an earth vertical axis, the time constant was longest (about 18 s) when the head was pitched forward to place the lateral canals near earth-horizontal and shortest (about 11 s) when the head was pitched backward to place the vertical canals near earth-horizontal. Finally, since during rotation in yaw the pattern of stimulation of the lateral and vertical semicircular canals varies with different head orientations one can use measurements of the horizontal component of the VOR, under varying degrees of pitch of the head, to calculate the relative ability of the lateral and vertical semicircular canals to transduce head velocity.

We studied two patients who could make saccades of normal velocity and amplitude only in association with a simultaneous blink. In one patient, the initiation of saccades was also facilitated by blinks. Both patients had signs of cerebellar or brainstem dysfunction, suggesting a posterior fossa localization for blink facilitation of saccadic velocity and amplitude.

The rotational vestibulo-ocular reflex (rVOR) contributes to gaze stabilitization by compensating head rotational movements sensed by the semicircular canals (SCC). The CNS improves the performance of the horizontal rVOR through the so called velocity storage mechanism (VSM). However the properties of the VSM in response to pitch rotations are less well known. We recorded eye movements evoked by whole-body constant-velocity pitch rotations about an earth-horizontal, interaural axis in four healthy human subjects. Subjects were tumbled forward, and backward, at 60 deg/s for over one minute using a 3D turntable. In these conditions also the otoliths contribute to the perception of head rotation because they sense the changes in direction of the gravity vector. The vertical slow phase velocity (SPV) responses show the typical exponential decay of the rVOR and a residual, otolith-driven sinusoidal modulation with a bias. Here the estimates of the contributions coming from the otoliths and from the canals are based on a linear summation hypothesis. The time constants of the canal-driven vertical component of the SPV ranged from 6 to 9 seconds. These values are closer to those produced by the SCC alone than the typical 20 s produced by the VSM in the horizontal plane, confirming the relatively small contribution of the VSM to these vertical responses. We also show that the estimation method, while it may be not physiologically accurate, is easy to implement and leads to reliable results.

To improve the specificity and sensitivity of the clinical diagnosis of progressive supranuclear palsy (PSP, Steele-Richardson-Olszewski syndrome), the National Institute of Neurological Disorders and Stroke (NINDS) and the Society for PSP, Inc. (SPSP) sponsored an international workshop to develop an accurate and universally accepted set of criteria for this disorder. The NINDS-SPSP criteria, which were formulated from an extensive review of the literature, comparison with other previously published sets of criteria, and the consensus of experts, were validated on a clinical data set from autopsy-confirmed cases of PSP. The criteria specify three degrees of diagnostic certainty: possible PSP, probable PSP, and definite PSP. Possible PSP requires the presence of a gradually progressive disorder with onset at age 40 or later, either vertical supranuclear gaze palsy or both slowing of vertical saccades and prominent postural instability with falls in the first year of onset, as well as no evidence of other diseases that could explain these features. Probable PSP requires vertical supranuclear gaze palsy, prominent postural instability, and falls in the first year of onset, as well as the other features of possible PSP. Definite PSP requires a history of probable or possible PSP and histopathologic evidence of typical PSP. Criteria that support the diagnosis of PSP, and that exclude diseases often confused with PSP, are presented. The criteria for probable PSP are highly specific, making them suitable for therapeutic, analytic epidemiologic, and biologic studies, but not very sensitive. The criteria for possible PSP are substantially sensitive, making them suitable for descriptive epidemiologic studies, but less specific. An appendix provides guidelines for diagnosing and monitoring clinical disability in PSP.NEUROLOGY 1996;47: 1-9

Duane's retraction syndrome (DRS) is a congenital eye movement disorder characterized by marked limitation or absence of abduction, variable limitation of adduction, and narrowing of the palpebral fissure with retraction of the globe on attempted adduction. We have recently recorded and quantitated ocular motility in five patients with unilateral DRS. In all patients, abduction of the affected eye was greatly limited, whereas adduction was limited, whereas adduction was limited to a lesser degree. Abnormalities in saccadic velocities were found in both the affected eye and the sound eye. Results of testing of the vestibulo-ocular reflex, optokinetic nystagmus, and optokinetic afternystagmus showed notable asymmetry. Our results suggest that DRS is produced by a primary brainstem abnormality involving premotor structures.

The Neurology of Eye Movements, Edition 5, by R. John Leigh, M.D. and David S. Zee MD Foreword Chapter 1: A Survey of Eye Movements: Characteristics and Teleology Chapter 2: The Ocular Motor Periphery Chapter 3: The Vestibular-Optokinetic System Chapter 4: The Saccadic System Chapter 5: Smooth Visual Tracking and Fixation Chapter 6: Gaze Holding and The Neural Integrator Chapter 7: The Neural Basis for Conjugate Eye Movements Chapter 8: Eye-Head Movements Chapter 9: Vergence Eye Movements Chapter 10: Diagnosis of Peripheral Ocular Motor Palsies And Strabismus Chapter 11: Diagnosis of Nystagmus and Saccadic Intrusions Chapter 12: Diagnosis and Management of Vestibular Disorders Chapter 13: Disorders of Ocular Motility Due To Disease of the Brainstem, Cerebellum and Diencephalon Chapter 14: Disorders of Ocular Motility With Disease Affecting The Basal Ganglia, Cerebral Cortex, And In Systemic Conditions Appendix A: A Summary Scheme for the Bedside Ocular Motor Examination Appendix B: A Summary of Methods for Measuring Eye Movements Appendix C: Tables of Ocular Motor Findings in Hereditary Ataxias Appendix D: Table of Videos and their Legends

Article abstract-Eye movements were recorded from 20 mildly affected patients with Huntington’s disease (HD) who were divided into two groups, 10 patients with onset of symptoms before age 30 and 10 with onset of symptoms after age 30. In the younger onset group (HD 30) had peak saccade velocities lower than 300 deg/sec. Latencies for volitional saccades were greater than normal in the HD > 30 group, but were normal for the HD 30 group had an affected mother. These findings suggest that the pathophysiology of the slow saccades, initiation deficit, and excessive distractibility in HD are different. NEUROLOGY 1988;38427-431 In a recent study of eye movements in mildly affected patients with Huntington’s disease (HD), we found abnormalities of both the initiation of saccades as well as the ability to hold steady fixation.’ Most patients showed an increase in saccade latencies that was greater for saccades made on command (voluntary saccades) than for saccades made to the sudden appearance of a visual stimulus (reflexive saccades). All patients showed excessive distractibility; they had difficulty in suppressing a saccade to a suddenly appearing visual target even though they were instructed either to maintain straight-ahead fixation or to make a saccade in the direction opposite to the visual target. We attributed these abnormalities to involvement of the frontal eye fields or basal ganglia in HD. In the present study, we report further abnormalities of eye movements-saccade slowing andsaccade dysmetria-in the same group of patients, and compare these findings with their deficits in saccade initiation and in holding steady fixation. Slow saccades have been noted in patients with HD with a reported prevalence of 18% to 100%.2-10 While one study did seem to show a correlation between the age of the patient and the saccade ~elocity,~ few attempts have been made to correlate saccade slowing with other saccade abnormalities in HD or with patient age or severity or duration of illne~s.~J~J~ In contrast to the saccade initiation and the fixation deficits, which have been attributed to involvement of the basal ganglia or cerebral hemispheres, saccade slowing has usually been attributed to direct pathologic involvement of the intrinsic brainstem structures that generate the immediate premotor commands for saccadic eye movement~.~-~ Accordingly, to better understand the eye movement abnormalities in HD, we compared disor

We describe two patients with a lifelong history of oscillopsia only when following objects moving toward their left side. Neurologic examination was normal except for eye movements. The patients showed nystagmus during any tasks that required visual following toward the left (ie, smooth pursuit, optokinetic nystagmus, and vestibulo-ocular-reflex-suppression), but had no nystagmus during fixation of stationary targets or visual following tasks to the right. Eye-movement recordings showed waveforms during pursuit to the left that were typical of congenital nystagmus.

A beside test to evaluate suppression of vestibular nystagmus by fixation on an object that rotates with the patient's head is described.

In Reply. —We appreciate the comments by Dr Metz regarding our article. While we agree that one of the patients had a large esotropia and another patient was exotropic, these patients, nevertheless, represent "typical" examples of type 1 Duane's retraction syndrome, in that they had severe limitation of abduction, slight limitation of adduction, and narrowing of the palpebral fissure with retraction of the globe on attempted adduction. In addition, our fifth patient, who had an exotropia of 15 diopters at distance and 30 D at near, has subsequently undergone an autopsy, with pathologic findings of Duane's retraction syndrome. An article concerning these findings is presently in press. With regard to peak saccadic velocities determined for 20° abducting saccades, velocities were determined to and from the primary position toward the field in which abduction was limited rather than in the field in which abduction was limited, as the footnote to Table

R. H. S. Carpenter's second edition is a delight. As was the case with the original, it is written in an engaging style and is filled with even more insights into the "how" and "why" of the ocular motor system. The original text has been considerably expanded and revised. The book is about as up to date as a single-authored textbook can be in a field in which each year's presentations and abstracts at the Neuroscience and Association for Research in Vision and Ophthalmology meetings make the previous year's knowledge of ocular motor physiology nearly obsolete. I believe Movements of the Eye should be required cover-to-cover reading for ophthalmologists, neurologists, optometrists, psychologists, physiologists and others who want a detailed but readable overview of the field of eye movements and their implications for vision. The book is much more than a compendium of facts. It is suffused with Carpenter's own refreshingly