Summary:Congenital ptosis in humans has been associated with anisometropia, myopia, astigmatism, and amblyopia. Scientific evidence has shown that visual deprivation causes axial myopia in animals. This study using chicks was undertaken to investigate an animal model of congenital ptosis and the effects of lid position on ocular development. Eyelid ptosis was surgically induced in one eye each of white leghorn chickens within 48 hours after hatching. The chicks were raised under natural diurnal lighting. Thirty days after inducing ptosis, the chicks were killed and their eyes enucleated and photographed in a sagittal view. Computerized image analysis was used to measure the size of the globe along five axes. Globe size was significantly greater in the superior part of eyes with ptosis compared with control eyes. No other measurement differences were significant (p < 0.01). Thus, this study demonstrates that regional axial myopia is induced by eyelid ptosis in chicks.