EFFECTS OF APRACLONIDINE ON AQUEOUS-HUMOR DYNAMICS IN HUMAN EYES

Purpose: The mechanism by which apraclonidine, an alpha(2)-adrenergic agonist, lowers intraocular pressure (IOP) was evaluated in humans. Me thods: In a randomized, double-masked, placebo-controlled study, 0.5% apraclonidine was given topically twice daily for 1 week to one eye in each of 21 ocular hypertensive volunteers. The other eye was treated similarly with vehicle. Before and after 1 week of treatment, aqueous flow, uveoscleral outflow, fluorophotometric outflow facility, intraoc ular pressure, tonographic outflow facility, episcleral venous pressur e, and outflow pressure were either directly measured or mathematicall y calculated. Values were compared in treated versus contralateral con trol eyes and on baseline versus day 8 of treatment. Results: When com pared with both contralateral control eyes and baseline day, fluoropho tometric outflow facility in the apraclonidine-treated eyes increased by 0.09 to 0.10 mu l/minute/mmHg (P < 0.04), IOP decreased by 3.1 to 5 .2 mmHg (P < 0.0001), and outflow pressure decreased by 3.3 to 4.2 mmH g (P < 0.0001). When compared with baseline day only, aqueous flow in the apraclonidine-treated eyes decreased by 0.3 mu l/minute (P < 0.04) , and episcleral venous pressure decreased by 1.0 mmHg (P < 0.001), Ep iscleral venous pressure also decreased in the control eyes compared w ith baseline day by 1.3 mmHg (P < 0.001). When compared with contralat eral control eyes only, uveoscleral outflow in the apraclonidine-treat ed eyes decreased by 0.47 mu l/minute (P < 0.03). Tonographic outflow facility showed no change when compared with either contralateral cont rol eyes or baseline values. Conclusions: The apraclonidine-induced re duction in intraocular pressure was associated with an increase in flu orophotometric outflow facility, decrease in aqueous flow and decrease in episcleral venous pressure compared to baseline. The lack of a sig nificant difference in aqueous flow and episcleral venous pressure bet ween treated and contralateral control eyes may represent a contralate ral drug effect.