Physiological nystagmus in the cat.

Cats were prepared by the encephale isole technique. A small plane-mirror mount was sutured to each cornea without obstructing vision, and eye movements were recorded using the optical-lever method. The records showed physiological nystagmus similar to that in man, although the cats had fewer and smaller saccades. Some saccades were binocular, but usually they were uniocular. The fine tremor varied in frequency from 35–65 cps, averaging 50 cps, and in amplitude from 4–52 sec of arc, averaging 22 sec. Curare decreased and ultimately abolished eye movements and physiological nystagmus, whereas neostigmine increased them. Physiological nystagmus is therefore mediated by efferent neural stimulation of the eye muscles. Tremor was also recorded from the detached inferior oblique muscle, as well as from the eyeball with most of the extraocular muscles detached. Fine tremor was also found in finger pointing in man. The significance of physiological nystagmus to vision is briefly discussed.