Refractive State of the Eye of a Small Diurnal Mammal

Previous work dealing with the question of whether or not the eyes of small mammals are hyperopic has been restricted largely to the study of nocturnal animals such as the rat. In this study, refractive state of the eye of a small diurnal mammal, the ground squirrel, was measured by retinoscopy and from the electrophysiological response of retinal ganglion cells to grating targets. Both measurements show the squirrel to be emmetropic. We conclude that the refractive state of the eye is not a function of eye size per se , but rather a function of whether the animal is nocturnal or diurnal.