Abstract

Numerous studies have shown that depriving the eye of the young chicken of clear form vision always results in myopia. Deprivation is usually achieved by the use of a translucent goggle over one eye. However, manipulation of the early visual environment of birds does not always produce myopia. The application of lenses to produce positive and negative defocus of the image of the young chick eye results in the formation of hyperopia and myopia, respectively. Preliminary results show that astigmatic defocus can produce astigmatic refractive states. Also, the application of a translucent goggle to the eye of the young American kestrel (Falco sparverius) produces both hyperopia and myopia, although myopia predominates. Furthermore, the normal hatchling kestrel eye is myopic and not hyperopic as is the hatchling chick. Hence, emmetropia is approached from opposite directions in these two species during the first few days after hatching. These results indicate that models of refractive error development of the bird eye should be able to account for all refractive conditions.

© 1991 Optical Society of America