Eyeball retraction latency in the conscious rabbit measured with a new photodiode technique.

A new technique is described for accurate, reliable measurement of eyeball retraction in the rabbit. A narrow film strip, on which a linear light intensity grating has been exposed, is attached to a contact lens which is placed on the animal's cornea. The other end of the intensity grating slides between a photodiode and an LED. The contact lens-film grating assembly moves freely with eyeball retraction and relaxation, causing changes in photodiode output. This device appears to be well tolerated by the animal. Large amplitude eyeball retractions occur in response to air puff stimulation directed at the upper or lower eyelid and to periorbital shock. Average eye retraction latency to stimulation of the abducens (VI) nerve with a chronically implanted stimulating electrode was 5.3 ms (S.D. = 0.75 ms) in the conscious rabbit as measured with our device. Latency to periorbital electrical shock was 9.3 ms (S.D. = 2.1 ms). Eye retraction latency decreased with increasing shock amplitudes. Rabbits readily acquired classically conditioned eyeball retractions, monitored with this device, when a white noise auditory stimulus was paired with an air puff directed at the eyelid.