Morphological recovery in the reattached retina of the toad Bufo marinus: A new experimental model of retinal detachment

Background. The retinal pigment epithelium (RPE) of the toad (Bufo marinus) has been used in many studies as a model for understanding its role and interaction with the neural retina. The toad's retina has been used to establish a new in vitro model of experimental retinal detachment (RD) and replacement (26). It has been shown that the electrophysiological measures of retinal function recovered following complete RD. The toad was chosen because its RPE is similar to the mammalian RPE (12). In this report, light microscopy was used to characterize the morphologic changes that occur in the RPE and neural retina following RD/replacement and to correlate these findings with recovery of electrophysiologic function. Methods. Retinas from Bufo marinus were studied in vitro. The neural retina completely detached from the RPE and then replaced. At various times after replacement, neural retina-RPE tissues were processed for light microscopy. Results. At 30 min after replacement, the subretinal space was greatly expanded, and the apical processes that normally ensheath the rod outer segments were short and no longer contacted the rod outer segments. The RPE was swollen, contained many vacuoles and the apical surface was rounded. By 2 h after replacement, the subretinal space was significantly resorbed and contained many shredded rod outer segments; RPE cells were still swollen, although less. During the next 5-10 h, the number of phagosomes in the RPE cytoplasm increased and the number of shredded rod outer segments in the subretinal space decreased. RPE cells regained their normal size and interdigitation of apical processes and rod outer segments were observed. Conclusions. These results demonstrate the re-establishment of morphological interactions between the RPE and neural retina within hours following RD/replacement. Morphological recovery coincides with recovery of electrophysiologic parameters. This is a good model to investigate the retinal pigment epithelium (RPE) and neural retina mechanisms involved in retinal adhesion and recovery from retinal detachment.