Studies on ocular blood flow and retinal capillary permeability to sodium in pigs

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Abstract
A surgical technique developed in pigs permits access to the retinal venous plexus surrounding the optic nerve. The effect of surgery on ocular blood flow and capillary permeability was evaluated. Blood flow, determined by the labeled microsphere technique, did not differ significantly between operated and control eyes. Increased intraocular pressure in the operated eye reduced blood flow through the choroid and the anterior uvea in proportion to the reduction in perfusion pressure. In the retina a smaller reduction in blood flow occurred indicating that autoregulatory mechanisms are involved in the control of retinal blood flow. The capillary permeability to Na was studied by the single injection technique, using albumin as a reference substance. The fractional initial extractions from the choroidal and the retinal vessels were 0.77 and -0.001, respectively. The absence of a Na extraction from the retinal vessel indicates this part of the blood-retinal barrier was intact and the blood drained by the retinal plexus is not mixed with blood from other sources.