Mechanism of ocular hypotensive action of bimatoprost (Lumigan) in patients with ocular hypertension or glaucoma

Abstract

Purpose: To determine the mechanism of ocular hypotensive action of bimatoprost in patients with ocular hypertension or glaucoma.

Design: Double-masked, placebo-controlled, randomized, paired comparison crossover study of the effect of bimatoprost on aqueous humor dynamics.

Participants and controls: Twenty-nine patients with ocular hypertension or glaucoma.

Methods: Bimatoprost and a placebo were administered once a day, in the evening, for 7 days before assessment of aqueous dynamics using tonometry, Schiötz tonography, and fluorophotometry. Intraocular pressure (IOP) response to water drinking was measured.

Main outcome measures: Aqueous humor flow rate, outflow facility, and IOP.

Results: Intraocular pressure was lowered 29% in the morning and 33% at noon by bimatoprost. Aqueous humor flow was unchanged. Tonographic facility of outflow was increased 47% by bimatoprost relative to the placebo. Assuming an extraocular pressure of 8 mmHg and that extraocular pressure is not altered by bimatoprost, the calculated rate of pressure-insensitive outflow was increased 95% by bimatoprost. During the first hour after water drinking, bimatoprost dampened the IOP rise.

Conclusion: As was seen in healthy normal eyes, bimatoprost increased both the pressure-sensitive and the pressure-insensitive outflows of aqueous humor in patients with ocular hypertension or glaucoma. Bimatoprost had no significant effect on aqueous humor formation.