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.