The Demonstration of a Blood-ocular Barrier in the Albino Rat by Means of the Intravitam Deposition of Silver

When silver nitrate is administered to rats in their drinking water for many months, they develop a generalized argyria. In the central nervous system, the deposition of silver follows the pattern of the so called hematoencephalic barrier (Wislocki and Leduc, (2); Dempsey and Wislocki, (3)). The present observations concern the deposition of silver in the rat's eye, investigated by both light microscopy and the electron microscope. In the eye, silver is not detected in the specific neural elements of the retina. Instead, it is heavily deposited in the basement membrane of the epithelium of the ciliary processes and in Bruch's basal membrane between the choriocapillary layer and the retinal epithelium. Traces of silver are visible in the basement membranes of the retinal capillaries with the electron microscope, but cannot be identified with the light microscope. In all of these respects, the pattern of the silver resembles the mode of its deposition in the brain. The heavy accumulation of metal in Bruch's membrane and the ciliary processes is analogous to that observed in the chorioid plexuses, and the traces encountered in the walls of the retinal capillaries correspond to traces observed in the basement membranes of the cerebral capillaries. Hence, with respect to silver, the eye possesses a blood-ocular barrier similar to the hematoencephalic barrier. Silver appears to be restrained from entering the aqueous humor by a barrier in the basement membrane of the ciliary processes, from reaching the photoreceptor elements of the retina by Bruch's basal membrane, and from penetrating the inner layers of the retina by a barrier in the basement membrane surrounding the retinal capillaries.