Histological Study on the Congenital Microphthalmia of the Chick Embryo

Abstract

Serial sections of microphthalmic chick embryos were examined histologically. Specimens used were from the malformed chick embryos described in the previous report (Kitoh et al. 1978). The examination revealed that the microphthalmias observed in the chick embryos could be classified into two groups, based upon the extent of their abnormalities. The group I microphhtalmia possessed ocular structures which had remained from the early developmental stage. The neural retinae and optic nerves were not formed. In the unilateral microphthalmia of group I, the lens was observed as an encapsulated small spherical body consisting of round cells, without lens fibers. This type of lens seemed to derive from the pigment epithelium. Pigment epithelial cells may thus have migrated first toward the cornea, then were encapsulated and finally lost their pigment granules while being transformed into the lens. On the other hand, the bilateral microphthalmia of group I possessed a rudimentary lens which appeared to be derived from subsiding corneal epithelium. Group II microphthalmia consisted of cases in which the optic cups were formed and the neural retina was differentiated. However, many abnormal ocular structures were noted. The neural retina had irregularly shaped foldings and gave rise to a rosette-formation. In many cases, retinal cysts were formed from the everted retina, caused by incomplete closure of the choroid fissure. The optic nerve was not always formed. In many cases, the lens fused with the cornea, which had a thickened fibrous layer and no endothelium. The lens fibers shownd degeneration in the form of swelling or vacuolation.