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A. Trzcinka, P. A. Radenbaugh, D. M. Reed, S. E. Moroi; Variations in Aqueous Humor Flow Response to Topical Beta-Blocker in Normal Humans. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1583.
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Glaucoma is an intraocular pressure (IOP)-related optic neuropathy. Topical beta-blockers lower IOP by decreasing aqueous humor flow. However, patients vary in their response to this drug class. This study was designed to obtain pilot data on variations in aqueous humor flow response to topical timolol.
Subjects were enrolled in an IRBMED approved prospective, randomized fluorophotometry study. After instilling topical fluorescein in each eye, one eye was randomized to timolol 0.5% and the other eye to placebo. Aqueous humor flow was then calculated from scans of each eye performed hourly between 8 AM and noon. The flow rates were compared using the paired Student’s t-test with p-value of <0.05 determined to be statistically significant. The ordinary least squares regression test was used to model the relationship between aqueous flow values in placebo-treated and timolol-treated eyes.
We obtained data on 30 subjects (17 men, 13 women) with an average age of 35.2 ± 13.5 years. Inpatient setting was utilized to study 8 subjects and remaining 22 subjects were studied in outpatient clinic setting. The aqueous flow of placebo-treated eyes was 2.50 ± 0.71 µL/min. The timolol-treated eyes had significantly lower flow of 1.83 ± 0.52 µL/min (p<0.0001). The percent decrease in flow ranged from 0 to 68%. Comparison of aqueous humor flow in the placebo eye and percent suppression of flow after timolol treatment yielded r2 of 0.48.
As expected, timolol decreased aqueous humor flow, but there was variation in aqueous flow response. From our sample size, we found that individuals with higher aqueous flow demonstrated greater response to timolol compared to those with lower aqueous flow. Our next step is to determine if there is an association in timolol response variation and beta-adrenergic receptor genotypes.
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