The evolution of two groups of lesions produced by photocoagulation in the retina of the rhesus monkey was studied by ophthalmoscopy and by light microscopy. In the first group, the moderate lesions were comparable to those that have been considered by Curtin and Norton as "ideal" for the creation of chorioretinal adhesions in human subjects. In the second group, the severe lesions were comparable to lesions that had been proposed by Meyer-Schwickerath as producing chorioretinal adhesions in man. Histopathologically, no adhesions of the retina were observed in the lesions of the first group. Adhesions of the retina did occur in the lesions of the second group, but Bruch's membrane was intact in all lesions, and no direct contribution to these adhesions from the choroid was observed. Thus, these adhesions were not truly chorioretinal. Instead, they appeared to be a union between retinal glial cells and the RPE or between retinal glial cells and Bruch's membrane. Ophthalmoscopically, two types of hyperpigmentation were observed. The first was attributable to accumulations of pigmentladen macrophages. In lesions of moderate severity these macrophages formed a ring around the center, while in severe lesions they were present throughout the central region. The second type of hyperpigmentation was due to the presence of hyperpigmented cells of the RPE around the lesions and was observed in both moderately severe and severe lesions.
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