A photorefractive characterization of focusing ability of infants and young children.

The authors have used isotropic and orthogonal photorefraction to examine the focusing ability of 360 normal uncyclopleged infants and young children (ages, 2 mo to 5 yr). Photorefractive reflexes were recorded on 400 ASA color transparency film at 1.5 m, and the subject viewed the photographer's face located directly above the camera. The photographs of reflexes were projected at X 20 on a computer-driven digitizing tablet and converted to the ophthalmic prescriptions that would correct the subject for the camera distance. Using these prescriptions the authors established 95% confidence limits as a function of age for each of four different tests: net sphere of most defocused eye; cylinder of most astigmatic eye; difference in spheres between two eyes; and difference in cylinder between two eyes. Spheric defocus was found to decrease uniformly as a function of age, as did the cylinder of the most astigmatic eye. However, the symmetry of focus of the eyes, as judged by spheric and cylindric differences, was established within the first year of life. By relaxing the limits of each individual test, a test battery was constructed that was failed by 5% of the subject population, with the individual tests contributing in approximately equal proportions to the failure rate. The use of this test battery for detecting focusing conditions in infancy and early childhood that can lead to amblyopia is discussed.