The peripheral and central neural actions of clonidine in normal and glaucomatous eyes

The peripheral and central neural actions of clonidine on normal and glaucomatous eyes have been investigated. Threshold doses of clonidine applied topically induced a monotonic decrease of intraocular pressure in the treated eye and had no effect on the contralateral eye. With increased clonidine dose, a decrease of intraocular pressure occurred in the untreated eye, and there was a concomitant decrease of systemic arterial blood pressure. Analysis of aqueous humor dynamics showed that the ocular response to the peripheral and the central neural actions of clonidine were without effect on the tonographic coefficient of outflow facility. The episcleral venous pressure decreased in both the treated and the untreated eyes, but the changes were too small to account for the observed decrease of intraocular pressure. The results are consistent with the concept that both the peripheral and central ocular hypotensive actions of clonidine are mediated by an inhibition of adrenergic neurogenic vasoconstriction in the eye.