Direct measurement of retinal microvascular pressures in the live, anesthetized cat.

Microvascular pressures in retinal circulation were measured in living, anesthetized cat by the servonull micropuncture technique. Of the total vascular pressure drop 32% was in the segment proximal to the large retinal arteries when intraocular pressure was set at 10 mm Hg and decreased to 27% when intraocular pressure was increased to 20 mm Hg. The pressure in the retinal veins was substantially (> 7 mm Hg) greater than intraocular pressure at both values of intraocular pressure. There was negligible pressure drop within venous segment; however, the pressure drop from the retinal veins to the systemic veins was large and cannot be explained on the basis of a venous waterfall within the retina.