Differences in eye growth and the response to visual deprivation in different strains of chicken.

Several laboratories studying visual deprivation myopia in the domestic chick report varying degrees of axial elongation and myopia induced by similar visual deprivation techniques. In this study we tested the hypothesis that in different strains of chick the eyes respond differently to visual deprivation. We compared under identical conditions two strains of White Leghorn chick commonly used in ocular development research--the Cornell-K strain (K) and Washington H & N Strain (H/N). The normal development of the eye was found to vary significantly between these strains of White Leghorn chicks. The K strain normally develops flatter corneas, thicker lenses, and larger eyes than the H/N strain. The response to visual deprivation also varies significantly between strains. For example, we find that 2 weeks of visual deprivation in the K strain results in less elongation of the vitreous chamber and flattening of the cornea yielding lower levels of induced myopia compared to the H/N strain. Our results show that while visual experience clearly affects normal ocular development in both strains of chick, the nature of the effect depends upon not only the type and duration of the experience but the genetics of the subject population as well.