Robert D. Yee

Visual‐vestibular interaction and cerebellar atrophy

The vestibular and optokinetic ocular control systems were studied in 10 patients with cerebellar atrophy and in 10 normal subjects using (1) constant velocity optokinetic stimulation, (2) sinusoidal rotation in the dark, and (3) sinusoidal rotation in the light with a surrounding fixed optokinetic drum. The gain (maximum slow component velocity/maximum head or drum velocity) of induced nystagmus was calculated from electro-oculographic recordings. Optokinetic nystagmus was abnormal in seven patients and the average optokinetic gain in the patients was significantly (p < 0.01) less than that of the normal group. Three patients with “clinically pure” cerebellar atrophy had increased vestibular responses, and one patient with clinical signs of peripheral neuropathy had decreased responses, probably due to associated vestibular nerve disease. The average vestibulo-ocular reflex gain in patients did not differ significantly from controls (p > 0.05). Three patients had normal vestibular and optokinetic responses when tested independently, but had abnormal visual-vestibular interaction. These patients probably had selective disorders of the midline cerebellar pathways that mediate visual-vestibular interaction. By studying each system, both independently and during interaction, all patients were identified as abnormal, and a more precise anatomic localization of the atrophy was obtained.

A study of congenital nystagmus Waveforms

Eighteen patients with congenital nystagmus were studied with the techniques of electronystagmography and computer analysis. We found several complex waveforms of congenital nystagmus in the primary position of gaze above those of jerk and pendular nystagmus as defined clinically. An etiologic classification of motor fixation defect and sensory fixation defect nystagmus based on waveforms is not justified. Ocular tracking studies demonstrate that the smooth pursuit system is operational in congenital nystagmus and substantiate the belief that the fast component of jerk nystagmus is a corrective movement generated by the saccadic system. Patients with congenital nystagmus are able to produce voluntary saccades with normal velocity-amplitude relationships.

Eye movements in ataxia-telangiectasia.

The spectrum of eye movement disorders in six patients with ataxia-telangiectasia at different stages of progression was assessed quantitatively by electrooculography. All patients demonstrated abnormalities of voluntary and involuntary saccades. The youngest and least involved patient had significantly incresed reaction times of voluntary saccades, but normal accuracy and velocity. The other patients demonstrated increased reaction times and marked hypometria of horizontal and vertical voluntary saccades. Saccade velocity remained normal. Vestibular and optokinetic fast components (involuntary saccades) had normal amplitude and velocity but the eyes deviated tonically in the direction of the slow component. We conclude that patients with ataxia-telangiectasia have a defect in the initiation of voluntary and involuntary saccades in the earliest stages. These findings are distinctly different from those in other familial cerebellar atrophy syndromes.

Vestibulo-ocular reflexes in peripheral labyrinthine lesions: III. Bilateral dysfunction*

Measurements were made of the lesion-induced changes in vestibulo-ocular reflexes (VOR) to rotatory stimuli in a group of patients with bilateral peripheral labyrinthine lesions. All the patients had caloric responses that were below the confidence levels used for normal responses in our laboratory. Responses to rotatory stimuli were greatly decreased or absent at low frequencies of stimulation, but present to a much greater degree at the higher frequencies. Phase measurements showed an increase in relationship to the velocity of the stimulus; there was a corresponding shortening of the time constant as obtained from impulse response measurements. A parametric study indicated that the changes in the responses can be described by a decrease in the sensitivity coefficient and in the basic time constant of a simplified pendulum model equation of vestibular function. A theoretical analysis of the data using a new model for the organization of the vestibular pathways indicated that the preservation of the high-frequency responses was the result of adaptive changes brought about in the central vestibular pathways and/or changes in the receptor-neuron transduction characteristics. Thus, despite the almost complete absence of any caloric response, the vestibular system reflexes remained adequate to maintain gaze during normal head movements.

Vestibulo-ocular reflexes in peripheral labyrinthine lesions: II. caloric testing†

In a group of patients with unilateral labyrinthine dysfunction, the maximal velocity of the slow component response to caloric stimulation was compared with that to horizontal vestibular rotatory stimulation by a low-frequency stimulus. It was found that the larger the magnitude of the caloric response, the larger were the gain and sensitivity of the vestibulo-ocular reflex induced by physiologic stimuli. Rotary stimulation of patients with only one functioning inner ear provides information equivalent to that obtained from caloric stimulation and allows more rigorous quantification of the state of the vestibulo-ocular reflex.

INTERNUCLEAR OPHTHALMOPLEGIA IN THE CHIARI TYPE II MALFORMATION

We describe 3 cases of Chiari type II malformation presenting with bilateral internuclear ophthalmoplegia (INO). Although prominent, the INO was not an isolated sign in any of the patients; superimposed abduction paresis was present in 2, and deficits in smooth pursuit, optokinetic nystagmus, and vestibulo-ocular responses were present in 3. Two had hydrocephalus: 1 was clinically unchanged without therapy after 5 years; the other did not improve with shunting. Findings in our 3 patients, along with the 4 previously reported, confirm that INO is 1 manifestation of widespread brainstem or cerebellar dysfunction. Its origin is probably multifactorial, related to hydrocephalus, vascular compromise, direct neuronal distortion, or congenital neural malformation.

Management of a patient with orbital varices, visual loss, and ipsilateral glaucoma.

A man with congenital orbital varices developed progressive ipsilateral visual loss beginning at age 62. Work-up demonstrated elevated intraocular pressure, decreased outflow facility, and mildly elevated episcleral venous pressure in the affected eye. Initiation of adequate glaucoma treatment was associated with interruption of declining visual acuity and with expansion of the constricted visual field. Medical control of coexisting glaucoma should be attempted prior to consideration of surgical intervention in any patient with visual loss and an ipsilateral orbital varix.

Atypical retinitis pigmentosa in familial hypobetalipoproteinemia.

Of three patients with familial hypobetalipoproteinemia, a 42-yeear-old white woman, who was homozygous for this autosomal dominantly inherited disease, had no detectable serum betalipoprotein and had a marked retinal pigmentary degeneration characterized by ring scotomas by Goldmann perimetry, extinguished electroretinographic responses, delayed responses and elevated thresholds during dark adaptometry, and abnoramal cone thresholds. A 4-year-old daughter and a 28-year-old niece of the first patient, who wer heterozygous, had reduced but detectable levels of serum betalipoprotein and no significant retinal pigmentary degeneration. Unlike patients with autosomal recessively inherited abetalipoproteinemia (the Bassen-Kornzweig syndrome), none of our patients had significant neurologic of cardiac defects. Although the level of serum betalipoprotein might be correlated with retinal pigmentary degeneration in familial hypobetalipoproteinemia and abetalipoproteinemia, it appears that neurologic and cardiac defects are dependent on other factors.

Identification of the location of vestibular lesions on the basis of vestibulo-ocular reflex measurements

Quantitative analysis of electro-oculographic recordings of eye movement in response to precise visual and vestibular stimuli makes possible the differentiation of three categories of vestibular syndromes due to pathological changes in three different parts of the visual vestibulo-ocular reflex arc: (1) decreased vestibulo-ocular reflex gain (e.g., decrease in slow component velocity), but normal fast components and visual-vestibular interaction (labyrinth and eighth nerve); (2) normal slow component velocity but abnormal fast components to all stimuli (pontine or medullar reticular formation); and (3) normal slow component velocity to vestibulo-ocular stimulaton but abnormal visual-vestibular interaction as well as normal fast components (visual-motor pathways or cerebellum).

Comparison of vestibular subjective sensation and nystagmus responses during computerized harmonic acceleration tests.

A comparison was made between the phase of vestibulo-ocular reflex (VOR) responses to sinusoidal rotatory tests and the phase of the subjective sensation (SS) to rotation. A parallelism was found between the results of both sets of data such that they behaved in accordance with the prediction of the pendulum model of vestibular function. The time constant of the VOR (17.5 seconds) was longer, however, than that of the SS (13 seconds). Measurements in patients with unilateral labyrinthine pathology also showed comparable changes in both responses. One group of patients with complete unilateral labyrinthine paralysis showed an advance of the phase of the VOR and of the SS. However, phase measurements in the group of patients with only partial unilateral labyrinthine paralysis were not significantly different statistically from those of normal subjects.