Necrosis and apoptosis in neuroretina and pigment epithelium after diffuse photodynamic action in rats: a light and electron microscopic study.

Cell death in the rat retina has been shown to occur mainly along two distinct pathways after pressure-induced ischemia. The authors conducted a qualitative investigation to determine whether similar types of cell death could be identified after diffuse photodynamic injury and photothrombosis. After i.v. injection of rose bengal (40 mg/kg), the eyes of 21 albino rats were exposed to light for durations ranging from 2 to 15 minutes, at a light intensity of 15-17,000 ft-cd, with interposition of a Kodak Wratten gelatin filter #15. Survival times ranged from 15 minutes to 6 days. The specimens were studied by light and electron microscopy. We identified two types of retinal cell death in the neuroretina and in the retinal pigment epithelium (RPE). Type I cell death was consistent with necrosis, and type-II cell death showed many features of apoptosis. These observations may not be exhaustive. The patterns of retinal cell death in this model appeared to be identical with those found after pressure-induced ischemia. The morphology of apoptosis of the RPE is hitherto undescribed. This study corroborates the concept of a limited number of types of cell death in the retina after exposure to noxious stimuli of various kinds.