Destruction of anionic sites in blood-retinal barrier after retinal photocoagulation

The retinal pigment epithelial cells (RPE) have "tight junctions" at the apical side of the lateral wall between neighbouring cells and form physiological blood-retinal barriers. Recently, in addition to physiological barriers, charged barriers, consisting of anionic sites of cell membrane and its basement membrane, have been discussed. We performed weak retinal photocoagulation in rabbit eyes in order to break their charged barriers, and examined the repair process using a cationic probe, polyethyleneimine (PEI). Two days after photocoagulation, RPE cells were broken down and choriocapillaries were occluded with thrombi, and their anionic sites were lost. At one week after photocoagulation, structural reconstruction started from the edge of the photocoagulation area. In this area, proliferated RPE cells covered Bruch's membrane, but their charged barrier did not recover. Two weeks after photocoagulation, proliferated RPE cells covered Bruch's membrane over the entire photocoagulated area, and they obtained anionic charge. The present study revealed that retinal damage induced by weak laser photocoagulation was repaired within two weeks after photocoagulation with respect to the charged barrier.