Louis F. Dell'Osso

Congenital nystagmus waveforms and foveation strategy

Accurate eye movement recordings of sixty-five subjects with congenital nystagmus (CN) provides a firm foundation for the classification of the many types of wave-forms observed and results in objective definitions based on measurable quantities rather than subjective clinical impressions. The careful scrutiny of these records along with the utilization of laser-target retinal cinematography have yielded insights into the mechanism of this ocular motor instability.Prolongation of target foveation emerges as the dominant factor in many of the resultant waveforms. This enhances the visual acuity of the subject with CN. An additional observation, related to fixation bias reversals of the CN subject, may be a physiological indicator of foveal function.

THE EFFECTS OF AGE ON NORMAL SACCADIC CHARACTERISTICS AND THEIR VARIABILITY

Age effects on human saccadic eye movements were tested with infrared reflectance oculography in 34 subjects. In contrast to a prior report, only a slight non-significant change was observed in saccadic velocity and duration. An increase in saccadic latency comparable to that found in several previous reports was observed, however. All parameters showed considerable intersubject variability for both age groups. Decreased velocities or increased durations outside of these normal, broad ranges should be regarded as pathological for all subjects; they are not physiological effects of the aging process.

A new surgery for congenital nystagmus: Effects of tenotomy on an achiasmatic canine and the role of extraocular proprioception

PURPOSE Human eye-movement recordings have documented that surgical treatment of congenital nystagmus (CN) also produces a broadening of the null zone and changes in foveation that allow increased acuity. We used the achiasmatic Belgian sheepdog, a spontaneously occurring animal model of human CN and see-saw nystagmus (SSN), to test the hypothesis that changes induced by surgical interruption of the extraocular muscle afference without a change in muscle-length tension could damp both oscillations. METHODS An achiasmatic dog with CN and SSN underwent videotaping and infrared oculography in a sling apparatus and head restraints before and after all extraocular muscles (stage 1: 4 horizontal rectus muscles and stage 2 [4 months later]: 4 vertical rectus muscles and 4 oblique muscles) were surgically tenotomized and immediately reattached at their original insertions. RESULTS The dog had immediate and persistent visible, behavioral, and oculographic changes after each stage of this new procedure. These included damped CN and SSN, increased ability to maintain fixation, and increased periods of maintaining the target image on the area centralis over a broad range of gaze angles. CONCLUSIONS Severing and reattaching the tendons of the extraocular muscles affect some as-yet-unknown combination of central nervous system processes producing the above results. This new procedure may prove effective in patients with CN with either no null, a null at primary position, or a time-varying null (due to asymmetric, (a)periodic, alternating nystagmus). We infer from our results in an achiasmatic dog that tenotomy is the probable cause of the damping documented in human CN after Anderson-Kestenbaum procedures and should also damp CN and SSN in achiasma in humans. It may also prove useful in acquired nystagmus to reduce oscillopsia. The success of tenotomy in damping nystagmus in this animal suggests that the proprioceptive feedback loop has a more important role in ocular-motor control than has been appreciated. Finally, we propose a modified bimedial recession procedure, on the basis of the damping effects of tenotomy.

Clinical and ocular motor analysis of congenital nystagmus in infancy.

PURPOSE The purpose of this study was to identify the clinical and ocular motility characteristics of congenital nystagmus and to establish the range of waveforms present in infancy. BACKGROUND The clinical condition of congenital nystagmus usually begins in infancy and may or may not be associated with visual sensory system abnormalities. Little is known about its specific waveforms in infancy or their relationship to the developing visual system. METHODS Forty-three infants with involuntary ocular oscillations typical of congenital nystagmus were included in this analysis. They were evaluated both clinically and with motility recordings. Eye movement analysis was performed off line from both chart recordings and computer analysis of digitized data. Variables analyzed included age, sex, vision, ocular abnormalities, head position, null-zone or neutral-zone characteristics, symmetry, conjugacy, waveforms, frequencies, foveation times, and responses to convergence and to monocular cover. RESULTS Patient ages ranged from 3 to 18 months (average, 9.2 months). Seventeen patients (40%) had abnormal vision, 3 had a positive family history of nystagmus, 11 had strabismus, 16 (37%) had a head posture, 26 (60%) had null and neutral positions, 14 (33%) had binocular asymmetry, and all were horizontally conjugate. Average binocular frequency was 2.8 Hz, and average monocular frequency was 4.6 Hz. The waveforms were both jerk and pendular; average foveation periods in patients with normal vision were more than twice as long as those in patients with abnormal vision. CONCLUSIONS Common clinical characteristics and eye-movement waveforms of congenital nystagmus begin in infancy, and waveform analysis at this time helps with both diagnosis and visual status.

Dynamic properties of the human vestibulo-ocular reflex during head rotations in roll

We investigated the dynamic properties of the human vestibulo-ocular reflex (VOR) during roll head rotations in three human subjects using the magnetic search coil technique. In the first of two experiments, we quantify the behavior of the ocular motor plant in the torsional plane. The subjects eye was mechanically displaced into intorsion, extorsion or abduction, and the dynamic course of return of the eye to its resting position was measured. The mean predominant time constants of return were 210 msec from intorsion, 83 msec from extorsion, and 217 msec from abduction, although there was considerable variability of results from different trials and subjects. In the second experiment, we quantify the efficacy of velocity-to-position integration of the vestibular signal. Position-step stimuli were used to test the torsional or horizontal VOR, being applied with subjects heads erect or supine. After a torsional position-step, the eye drifted back to its resting position, but after a horizontal position-step the eye held its new horizontal position. To interpret these responses we used a simple model of the VOR with parameters of the ocular motor plant set to values determined during Exp 1. The time constant of the velocity-to-position neural integrator was smaller (typically 2 sec) in the torsional plane than in the horizontal plane (> 20 sec). No disconjugacy of torsional eye movements was observed. Thus, the dynamic properties of the VOR in roll differ significantly from those of the VOR in yaw, reflecting different visual demands placed on this reflex in these two planes.

Macro square wave jerks

Quantitative eye movement recordings in a patient with multiple sclerosis who had both macro square wave jerks and an internuclear ophthalmoparesis supported the concept of an internal brain-stem monitor that mediates corrective eye movements. A brain-stem model of this monitor illustrates the patients motility disorder and the normal function of providing synergistic version and vergence corrections for dysmetric eye movements. Thus, the careful study of pathologic disturbances provides information relevant to the normal operation of the ocular motor system.

Ocular motor abnormalities in achiasmatic mutant Belgian sheepdogs: Unyoked eye movements in a mammal

We studied the eye movements of several members of a family of Belgian sheepdogs that includes achiasmatic mutants. Our aim was to identify the types of nystagmus and other ocular motor abnormalities exhibited by the mutants. We also recorded from several unaffected heterozygous carriers of the genetic mutation and from a normal Irish Setter. Mutant dogs exhibited nystagmus waveforms that were occasionally similar to those of humans with congenital nystagmus (CN). Foveating and braking saccades and foveation periods were seen in some waveforms. More common were pendular oscillations of both eyes that were essentially independent in amplitude and phase. At some times there was a pendular nystagmus with a 180 deg phase shift between the movements of unaffected relatives did not reveal any saccadic instabilities. However, small saccadic intrusions could have been masked by quantization artifacts. Individual dogs from this family provide an animal model of the ocular motor consequences of the disturbed visual input caused by the absence of an optic chiasm and a novel model of CN. Despite any other ocular motor abnormalities present, the CN may be studied in isolation just as in humans it is studied when strabismus and other types of nystagmus are present. Further studies of ocular motor development and function in achiasmatic dogs have the potential to reveal both the organization of the control systems for each extraocular muscle and the role of yoking of the agonist muscles of the two eyes.

Myasthenia gravis: Saccadic eye movement waveforms

Abstract The study of the refixational saccadic eye movements of 10 patients with myasthenia gravis revealed large intra-and intersubject variability and a diversity of waveforms necessitating the development of a recursive classification scheme which separated the dynamics of the eyes trajectory and the metrics of the completed movement. The waveforms reflected the admixture of the primary peripheral myasthenic deficit and compensatory central adaptation to it. Whenever possible, the peripheral and central factors were identified for each waveform component. The prevalence of multiple, closely spaced saccades and dynamic overshoots in this population coupled with their absence in other peripheral disorders, suggests a possible role for proprioception in ocular motor control.

Foveation Period Stability And Oscillopsia Suppression In Congenital Nystagmus: An Hypothesis

Congenital nystagmus (CN) waveforms contain foveation periods that occur just before the eyes accelerate away from the target and occur when the eye is in position to place the target image, most of the time, on the fovea. Using phase-plane analysis, the authors studied the waveform changes in an individual with hereditary CN who experienced intermittent oscillopsia (OSOP) following an episode of loss of consciousness six years previously. His nystagmus showed two waveforms that alternated approximately every 2 sec. One waveform (with leftward fast phases) provided repeatable, well-developed foveation periods lasting typically 114 msec, during which the image of an object of regard was within 0.5° of the center of the fovea and image drift was 20°/sec as the image of the object of regard sw...

Myasthenia gravis: Dynamic changes in saccadic waveform, gain, and velocity

The effects of refixation fatigue, maintained gaze fatigue, and intravenous edrophonium on saccadic waveform, gain, and velocity were studied in 10 patients with ocular myasthenia gravis. Refixation fatigue was minimal. Gaze maintenance had four separate but differing effects on waveform and gain; normalized peak velocities did not decrease. Edrophonium caused hypermetria and increased gain but normalized peak velocities were either unchanged or decreased. These effects represent, in part, selective impairment of the tonic, as distinct from phasic, fibers in the extraocular muscles and compensatory increase in central saccadic gain induced by the muscle weakness.