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Show ! ournal of Clinical Neuro- ophthalmology 11( 3): 166- 168, 1991. The Effect of Chronic One- Eye Patching on Ocular Myoclonus Yuval O. Herishanu, M. D. and Raoul Zigoulinski, M. D. © 1991 Raven Press, Ltd., New York Ocular myoclonus developed in our 34- year- old patient 4 months after massive brain stem hemorrhage due to eclampsia, On chronic patching of the left eye, the vertical pendular nystagmus in the fixating right eye disappeared, whereas the covered eye was esotropic. While fixating, the left eye showed horizontal pendular nystagmus. With both eyes fixating, the right eye presented markedly vertical pendular nystagmus and the left eye a horizontal pendular nystagmus. It seems that chronic patching of one eye has a beneficial modulating effect on the vertical pendular nystagmus in the fixating eye. Key Words: Ocular myoclonus- Eye patchingNystagmus. . From the Department of Neurology, Soroka University Medical Center, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer- Sheva, Israel. Address correspondence and reprint requests to Dr. Y. O. Henshanu at Department of Neurology, Soroka Medical Center, P. O. Box 151, Beer- Sheva, Israel. 166 Ocular myoclonus may develop after a brain stem lesion, and the movements of the eyes as well as the associated myoclonus of the palate, vocal cords, diaphragm and limbs are attributed to disruption of the connection between the dentate nucleus, contralateral red nucleus, and inferior olivary nucleus ( 1). Few cases have recovered spontaneously. Therapeutic trials have met with variable success. 5Hydroxytryptophan in combination with carbidopa ( 2), carbamazepine ( 3), clonazepam ( 4), and trihexyphenidyl ( 5) improved palatal myoclonus. Amobarbital ( 6), diazepam ( 7), scopolamine ( 8), and trihexyphenidyl ( 9) improved vertical pendular nystagmus. This paper reports the changes in the amplitude and the direction of the ocular myoclonus that occurs with chronic patching of one eye. CASE REPORT A 34- year- old patient [ whose history was previously reported by Herishanu and Louzoun ( 9)] presented in the 32nd week of pregnancy with severe toxemia of pregnancy which led to generalized tonic convulsions controlled with diazepam and magnesium sulfate. This was followed by a stuporous state accompanied by left hemiparesis. Cesarean section was performed. Several hours later she was alert but presented dysarthria, bilateral horizontal gaze palsy on volition and reflex stimulation, slight limitation of upward gaze, and skew deviation. Downward gaze was possible but down- beating nystagmus was present. The fundi were normal. Right peripheral facial palsy, decreased right pharyngeal reflex, left flaccid hemiparesis with overactive tendon reflexes, left extensor plantar response, and decreased perception of all modalities were also found. ONE- EYE PATCHING AND OCULAR MYOCLONUS 167 Computed tomography showed massive bleeding into the brain stem from the pons to the midbrain. She gradually improved. Two months later there still was marked limitation of gaze to the right and to the left, whereas upward and downward gaze and convergence were normal. Four months after the onset, she noted vertical oscillopsia and presented marked vertical pendular nystagmus. On upward gaze the nystagmus decreased in amplitude and on downward gaze the nystagmus became horizontal with a rotatory component. No palatal myoclonus was found at that time. Artane markedly reduced the amplitude of the nystagmus, but the patient stopped this treatment after 1 year because of psychomotor irritability. The patient was advised by a general practitioner to cover one eye with a patch. She covered the left eye, and 3 months later a marked decrease in the amplitude of the vertical pendular nystagmus in the right uncovered eye was seen. On different occasions, the eye movements were recorded using a Nihon Kohden Electronystagmograph, an infrared reflection device ( Eyetrac 200), and video. Three years after first patching her left eye, the right eye, kept uncovered, is free of nystagmus. There is limitation of right eye adduction and absent right eye abduction. When the left eye was unpatched, this eye was found to be markedly esotropic (+ 25 ~ distance and near). Corrected visual acuity was 20/ 20 in both eyes. When the right eye was patched, horizontal pendular nystagmus of the left eye was seen. On attempted right gaze, a very slight movement was elicited- more with the left eye. On attempted left gaze, only slight adduction of the right eye was seen. With both eyes uncovered, the right eye showed vertical pendular nystagmus, and the left eye executed an horizontal pendular nystagmus. On upward gaze, oblique pendular nystagmus was noted. On downward gaze vertical pendular nystagmus of both eyes was seen. Palatal myoclonus was still present. Head titubation and left arm postural tremor with a same rhythm as the nystagmus were also seen. DISCUSSION In a few cases, ocular myoclonus was reported to disappear spontaneously ( 10- 12). In all other cases, ocular myoclonus does not change unless pharmacologically treated. . In this case, the ocular myoclonus changed Its characteristics on long term follow- up as a result of one- eye patching, i. e., it disappeared in the uncovered eye while the covered eye became esotropic. This finding shows some similarity to the nystagmus blockage syndrome that has been well documented in a few cases of congenital nystagmus ( 13). On follow- up our patient presented bilateral horizontal gaze paresis with a slightly more limited abduction on both sides. The latter finding can be explained by damage to the abducens nerve fascicles, which in turn probably explains the esotropia of the occluded left eye. We presume that the esotropia " blocked" the nystagmus in the fixating eye. During binocular viewing of a distant target for awhile, the esotropia almost disappeared and the nystagmus recurred in both eyes. The possibility of tactile feedback from the inner eyelid reducing the nystagmus in the fellow eye ( 14) can be ruled out, since the effect of attaching the patch to the eyeglass was the same as that of attaching the patch to the eyelid. When the right eye was covered and the left eye was fixing, the left eye presented horizontal pendular nystagmus. Changes in the vectors of the horizontal saccades in the patched eye were reported in studies on monkeys ( 15). In the light of our findings, it seems that patching of one eye might be beneficial in alleviating this disturbing symptom in similar patients suffering from ocular myoclonus. REFERENCES 1. Guillain G, MoUaret P. 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