The concept of a blood retinal barrier is still relatively new in the ophthalmic literature. fuereas work on the blood-brain barrier was initiated in the first decade of this century, the blood- retinal barrier has only recently been defined. Information accu- mulated during the last 10 years has shown that the function of the blood-ocular barriers may be better understood if two main barrier systems are considered to exist in the eye. The blood-aqueous barrier regulates the exchanges between the blood and the intraocu- lar fluids, and the blood-retinal barrier separates the neural tissue...