SCANNING AND TRANSMISSION ELECTRON-MICROSCOPIC FINDINGS DURING RPE WOUND-HEALING IN-VIVO

Objective: To examine the scanning (SEM) and transmission (TEM) electr on microscopic features of an in vivo rabbit model of retinal pigment epithelial (RPE) wound healing. Methods: Hydraulic debridement of the RPE was performed in one eye of each of 35 pigmented rabbits using a p ars plana vitrectomy approach. Five of the 35 eyes were examined by ei ther SEM or TEM on each of the following postoperative days: 0, 2, 4, 7, 14, 28 and 56. Results: TEM revealed that hydraulic RPE debridement results in only focal damage to the RPE basement membrane portion of Bruch's membrane and that this damage is repaired by day 7 without ult rastructural sequelae. SEM and TEM disclosed that the RPE cells at the margin of the debrided bed become flattened and enlarged and evolve a cytoskeletal reorganization with altered apical-basal polarity consis tent with the development of a migrating phenotype. This is followed b y gradual restoration to a more normal stationary RPE phenotype after initial closure (reepithelialization) of the RPE defect on day 7. RPE hyperplasia also occurs and may contribute to this repair process. Tig ht junctions are re-established among the apical surfaces of monolayer ed and multilayered RPE cells by day 7, coinciding with the restoratio n of the blood outer retinal barrier. Conclusion: Hydraulic debridemen t of the RPE in vivo is a useful investigational model that provides i mportant insight into the pathogenesis of outer retinal disorders and their treatment with such techniques as submacular surgery or RPE tran splantation.