An Incidental Retinal Dysplasia in the Rat and its Preliminary Experimental Study

Abstract

One rat of the Crj: CD strain, 16 weeks of age, was found to have eye abnormalities characterized by retinal dysplasia, typical coloboma, and retinocele possibly due to a failure of closure of the optic fissure.

Fundus examination of the eyes of the rat revealed a well delineated grayish area around the optic disk, an elongated papilla, and a hyaloid artery remnant. These findings were observed symmetrically in the fundus of both the right and the left eye. Histopathological examination revealed disorganization of the retina forming rossette, lack of rods, cones, stratum pigment layer and choroid, herniation of the retina into the sclera, and a hyaloid arterial remnant forming a loop with the retinal arterioles.

Exploratory studies have been conducted in this laboratory to induce experimentally a failure of closure of the optic fissure in rat and mouse embryos with Ochratoxin A. The induced changes were rosette formation and folding associated with derangement of the cell layer in the inner layer of the optic cup, and defect of the pigmented epithelial layer and the choroid due to irregular development of the inner and/or outer layer of the cup. These changes were mostly comparable to the changes observed in the adult Crj: CD rat.

From the above experimental results, we conclude that one of the major causes for the congenital retinal dysplasia, coloboma, and retinocele observed spontaneously in the adult rats is failure of closure of the optic fissure.