Fluid permeability of monkey ciliary epithelium in vivo

Four months after total iridectomy, the aqueous humor of each of six cynomolgus monkeys was perfused at the spontaneous intraocular pressure under urethane anesthesia. The perfusate solution consisted of mock aqueous humor containing trace amounts of 14C-dextran (70,000 mol. wt.). The aqueous was stirred to bathe the ciliary epithelium. Aqueous flow was calculated from the tracer dilution. The aqueous humor was then perfused with bovine serum albumin (35 mg/ml) added to the perfusate. A new aqueous flow value was determined. Aqueous flow during mock aqueous perfusion was 1.28 +/- 0.12 microliters/min and 1.64 +/- 0.12 microliters/min during mock aqueous plus albumin perfusion. From the increase in aqueous flow due to the osmotic effect of the albumin solution (13.2 mm Hg), the osmotic fluid permeability of the ciliary epithelium was calculated to be 0.027 +/- 0.007 microliters/min/mm Hg. This permeability value places the ciliary epithelium in the category of membranes with "leaky" tight junctions. However, the low fluid permeability of the ciliary epithelium suggests a minor role for ultrafiltration in aqueous humor formation in the monkey.