Folding of photoreceptor cell layer: a new form of retinal lesion in rat.

A new form of retinal lesion has been observed in rats. It is characterized by inward folding of the photoreceptor cell layer (outer nuclear layers); microretinal detachment; thinning of inner retinal layer; loss of Muller cells in the lesion; in most cases, normal retinal surface contour, and no increase in total retinal thickness. Remarkable strain differences were noted. In Sprague-Dawley rats, the incidence increases with age, and lesions are more often located in the peripheral one third. On the other hand, in rat strains having known hereditary retinal disorders (Wag/Rij and Wag/Long-Evans), the incidence of lesions decreases with increasing age of observed specimens, and the lesions are more frequently located in the posterior one third. These new forms of retinal lesions differ from retinal folds found in the far periphery of the developing retina. Our findings suggest that loss of Muller cells in the lesions initiates this disorder.