Ocular vascular and epithelial barriers to microperoxidase.

Microperoxidase (MP) is an ultrastructural tracer of small molecular weight (1,900) derived from horse heart cytochrome c. Within the central nervous system, it is capable of entering the periaxonal space which is not open to horseradish peroxidase (HPR). Because of its small size and unique behavior, MP was used to probe ocular vascular and epithelial barriers. MP did not enter any ocular space from which HRP was excluded. This tracer established a new lower level of permeability in these ocular barrier systems.