Refractive state, depth of focus and accommodation of the eye of the California ground squirrel (Spermophilus beecheyi).

Retinoscopy and electrophysiological refraction were performed on 55 and 24 far-accommodated eyes of California ground squirrels (Spermophilus beecheyi), respectively. These two indices were highly correlated, revealing the eye of this animal to be roughly emmetropic (-0.25 to -0.13 D). Depth of focus was assessed by measuring the effect which defocusing produced on the spatial resolving power of 32 optic nerve fibers. Depth of focus of the ground squirrel eye for a pupil diameter of 2.5 mm is estimated to be +/- 1.6 D, but will increase rapidly for smaller pupils. Accommodation in eleven ground squirrels ranged from 2 to 6 D, with a mean value of 3.9 D.