Photic maculopathy in rhesus monkey. A light and electron microscopic study.

Photic maculopathy was produced in rhesus monkeys after exposure to the light of an indirect ophthalmoscope for one hour. This experimental model provided an opportunity for light and electron microscopic study of a relatively mild photic insult to the macula. During the first week, there was retinal edema with damage to the photoreceptor cells and to the retinal pigment epithelium. Beginning in the second week, an influx of macrophages to the subretinal region was observed. Later the macrophages left the site of injury by way of the choroidal circulation. Depigmented retinal pigment epithelium remained. After the first month, active repair and regeneration took place. A placoid proliferation of the retinal pigment epithelium developed in the center of the lesions. Histologically such proliferation resembled "fibrous metaplasia" of retinal pigment epithelium in man, but electron microscopy showed that the cells retained their epithelial characteristics. Macrophages were still present between the proliferated cells of the retinal pigment epithelium five months after exposure. The photoreceptor cells overlying the depigmented and proliferated retinal pigment epithelium regenerated their outer segments. This study demonstrated that the photoreceptor cells can regenerate their outer segments and provided an explanation for the observation that patients with solar retinitis can show gradual but remarkable recovery.