[Detection of destruction of anionic sites in the outer blood-retinal barrier and damage caused by iron]

We studied the alteration of the anionic charge in the outer blood-retinal barrier in ocular siderosis by electron microscopy using the cationic probe, polyethyleneimine (PEI). The eyes of four days after injection of iron powder and control rabbit eyes demonstrated numerous PEI-positive sites at the basement membrane of the retinal pigment epithelium, collagen fiber of Bruch's membrane, and the basement membrane of the choriocapillaris. Seven days after injection of iron powder, no change was observed in the retina by light microscopy, but PEI positive sites at the basement membrane of the retinal pigment epithelium were decreased. At 14 days, it was seen that the outer layer of the retina disappeared and was replaced by pigment containing macrophages and Müller cells. Berlin blue reaction became positive in some of those macrophages and retinal pigment epithelia. PEI positive sites decreased. At 28 days, the retina was completely disorganized, and became thin, while the retinal pigment epithelium proliferated and became double layered. Berlin blue reaction was strongly positive in pigment-laden macrophages and retinal pigment epithelium. PEI-positive sites became scarce. As a result of these methods, anionic sites decreased, despite negative iron reaction of 7 days after injection of iron powder. It was shown that in ocular siderosis at an early stage, the barrier function of anionic sites between choroid and retina decreased before histological change.