Effects of retinal image degradation on ocular growth in cats.

High-powered negative and positive contact lenses have been used to produce a state of continuous retinal defocus in the eyes of 11 kittens in an attempt to induce a predictable amount of axial lengthening and myopia. Another group of six kittens had one eye continuously atropinized and a third group of four animals had the lids of one eye sutured. The axial dimensions and refraction were measured using ultrasonography and retinoscopy respectively. Although the treated eyes of eight kittens tested behaviorally were shown to be amblyopic, no myopia appeared in any animal at any stage during development and only three cats showed a small axial length difference between the two eyes. These results differ from other retinal deprivation studies reported on kittens and no satisfactory explanation for this discrepancy can be offered. However, it is suggested that the lack of change may be associated with the gross anatomy of the cat's eye, and it is concluded that myopia cannot be induced reliably in kittens by retinal image degradation.