Optokinetic nystagmus in albino rats depends on stimulus pattern.

Ocular responses to optokinetic stimulation were reexamined in adult albino rats of two different strains. Eye movements were measured in head-restrained animals using the search coil method. In contrast to some previous results, the albino rats showed optokinetic nystagmus, and some of them made responses comparable to those previously recorded from pigmented rats. However, the type of stimulus pattern used to elicit optokinetic nystagmus proved to be crucial for albino rats. The deficit is attributed to abnormalities in the albino rat's visual sensory apparatus. Inverted optokinetic nystagmus was elicited in albino rats by restricting the optokinetic stimulation to the anterior visual field of both eyes. The same phenomenon has been observed previously in albino rabbits and mice, and has been suggested to be due to the abnormally small number of uncrossed optic nerve fibers in albinos.