Mechanisms of accommodation in the bird eye

Abstract

Keratoscopic study of corneal curvature before and after accommodation in two common bird species failed to provide evidence of a corneal accommodative mechanism. Accommodative changes in refractive state measured retinoscopically are presumably brought about by the effect of ciliary muscle contraction on lens curvature. However, retinoscopic and freeze-sectioning study of accommodation in diving ducks supports the long suspected existence of an iris accommodative mechanism capable of producing dramatic changes in lens curvature. This mechanism is believed to be a means of compensating for the refractive loss of the cornea in water.