Repair after xenon arc photocoagulation. 3. An electron microscopic study of the evolution of retinal lesions in rhesus monkeys

The evolution of two groups of retinal lesions produced by photocoagulation in the eyes of the rhesus monkey was studied by electron microscopy. In the first group, Müller cells in the lesions became hypertrophic, filled the retinal defect, and reformed an outer limiting membrane. No adhesion to the retinal pigment epithelium developed. In the second group, proliferated retinal astrocytes originating from the viable edges of the lesions provided repair and formed a glial scar. The proliferated glial cells tended to re-form the plane of the neural retina but were also frequently associated with a new adhesion of the neural retina. Two types of adhesion were seen. In the first type, glial cells were joined to proliferated cells of the retinal pigment epithelium either along the outer aspect of the repaired retina or within the glial retinal scar. In the second type glial cells became intimately aligned along the cuticular portion of Bruch's membrane. Two types of hyperpigmentation of the lesions were observed. In the first, it was attributable to pigment-laden macrophages. In the second, it was accounted for by an accumulation of electron-dense material within cells of the retinal pigment epithelium. This material belonged to the group of cytoplasmic particles that include phagolysosomes, residual bodies, and lipofuscin granules. New formation of melanin was not observed.