Effect of thymoxamine on aqueous humor formation in the normal human eye as measured by fluorophotometry

A double-blind, randomized, placebo-controlled study of the effect of 0.5% topical thymoxamine hydrochloride an alpha-adrenergic antagonist, on the rate of aqueous humor formation in the eyes of 25 normal human subjects was performed with fluorophotometry. The effect of thymoxamine on intraocular pressure and anterior chamber volume was also studied. four of the 25 subjects were used to study the effect of thymoxamine on the permeability to fluorescein of the blood-aqueous barrier. Pupillography was used to confirm that alpha blockade was present in the iris. Thymoxamine-treated eyes had 12% greater aqueous humor flow than placebo-treated eyes, but this difference was not statistically significant. No statistically significant difference was found in the rate of aqueous humor formation, intraocular pressure, anterior chamber volume, or premeability of the blood-aqueous barrier between thymoxamine-treated and placebo-treated eyes. The lack of an effect on the aqueous system could be interpreted as being a result of too low a concentration of thymoxamine in the ciliary body, lack of blockable receptors in the ciliary body, lack of physiologic tone in a blockable receptor system, or lack of a role of such a receptor system in the formation of aqueous humor.