CONSTANT LIGHT PRODUCES SEVERE CORNEAL FLATTENING AND HYPEROPIA IN CHICKENS

In this study we report on the effects of constant light (CL) on the r efractive development and ocular morphology of White Leghorn chicks (C ornell IC-strain). Refractive state and corneal curvature were measure d by IR photoretinoscopy and IR keratometry respectively. The axial le ngths of the ocular components were measured by A-scan ultrasonography . We find that constant Light produces significant hyperopia compared to controls in as few as 10 days (7.4 vs 4.0 D). This is apparently th e result of flatter than normal corneal curvature (radius of curvature : 3.22 vs 3.08 mm) as vitreous chamber depth is significantly deeper i n CL eyes than controls at that age (5.6 vs 5.1 mm). In contrast to ot her reports, if CL rearing is continued for longer periods the hyperop ia progresses, even though vitreous chamber depth continues to increas e. After 11 weeks of CL severe hyperopia was observed (18.2 vs 2.8 D). Long term CL is also found to produce shallow anterior chambers, corn eal thickening, lenticular thinning and cataracts, and damage to the r etina, pigment epithelium, and choroid.