Permeability of blood-ocular barriers of neonatal and adult cats to fluorescein-labeled dextrans of selected molecular sizes.

The permeability of the ocular blood vessels and neuroepithelial layers (the blood-ocular barriers) to fluorescein-labeled dextrans of selected molecular sizes was evaluated in neonatal and adult cats by fluorescence microscopy. The iris and ciliary process vessels were permeable to molecules as large as 85A effective diffusion radius (EDR). In the kitten, the choriocapillaris was permeable to molecules as large as 58A EDR, and in the adult to molecules only as large as 32A EDR. The retinal vessels and the retinal pigment epithelium were impermeable to all markers. The role of the cat's iris vessel in aqueous humor formation appears dissimilar to that of other species in that molecules larger than serum proteins traverse the walls of the iris capillaries.