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Honrubia, MD Article abstract-We found a selective loss of vestibular hair cells in a patient followed for more than 10 years with imbalance and oscillopsia due to idiopathic progressive loss of vestibular function. Hearing function and cochlear hair cells were normal. The vestibulo-ocular reflex (VOR) gain at high frequencies was relatively maintained despite marked shortening of the dominant VOR time constant (to less than 500 ms). Ultrastructural examination of remaining hair cells showed mitochondria1 abnormalities. The ultrashort VOR time constant probably resulted from changes in firing patterns of the primary afferent nerves due to loss of hair cells and impaired energy metabolism in remaining hair cells. NEUROLOGY 1997;49:1377-1382 If a normal subject is rotated in the dark at a con- stant velocity for about a minute and then suddenly stopped, a postrotatory nystagmus occurs with a slow phase in the direction of prior rotation. Accord- ing to current models of the vestibulo-ocular reflex (VOR) the velocity of the slow phase of this nystag- mus will decay exponentially with a time constant (defined as the time for the response to attain 37% of " From the Department of Neurology (Dr. Baloh) and the Division of Head and Neck Surgery (Drs. Baloh, Lopez, Ishiyama, and Honrubia, and K. Beykirch), UCLA School of Medicine, Los Angeles, CA. Supported by NIH grants DC02952 and AG09693. Received February 19, 1997. Accepted in final form May 28, 1997. Address correspondence and reprint requests to Dr. Robert W. Baloh, UCLA Department of Neurology, Box 951769, Los Angeles, CA 90095-1769. Copyright zyxwvu 0 1997 by the American Academy of Neurology 1377