Chick eye optics: zero to fourteen days

Ocular dimensions and refractive state data for chicks 0 to 14 days of age were obtained from 234 untreated control eyes of birds treated unilaterally in previous work involving various defocussing lenses and/or translucent goggles. Refractive state and corneal curvatures were measured in vivo by retinoscopy and ophthalmometry respectively. Intraocular dimensions were measured by A-scan ultrasonography, after which the eyes were removed, weighed and measured. In some cases (n = 52) intraocular dimensions and lens curvatures were obtained from frozen sections of enucleated eyes. The hyperopia of hatchling chicks (+6.5 +/- 4.0 D) initially decreases rapidly and then more gradually to +2.0 +/- 0.5 D by 16 days. The distribution of refractive errors is very broad at Day 0, but becomes leptokurtotic, with a slight myopic skew, by Day 14. Corneal radius is constant for the first four days, possible as a result of pre-hatching lid pressure, and then increases linearly, as do all lens dimensions, axial diameter and equatorial diameter. Schematic eyes were developed for Days 0, 7, and 14.