Effect of visual environment on refractive error of cats

33 eyes of 18 cats raised in cages or in small rooms under conditions of near vision were compared with 22 eyes of 11 street cats. Refraction of the caged cats showed that three quarters of them were myopic (average:-0.8 D) while 87.5 percent of the street cats were hypermetropic (average: +1.4 D). The antero-posterior diameter was practically equal in both groups (20.4 mm) and in both myopic and hypermetropic eyes. The site of the permanent refractive changes is suggested to be the lens.