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V. Gulati, C. B. Toris, D. A. Ghate, C. B. Camras; The Effect of Baseline Aqueous Humor Dynamics on the Ocular Hypotensive Efficacy of Latanoprost or Timolol. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2034.
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Latanoprost(LP) and timolol are two of the most effective and commonly-used drugs in glaucoma therapy. They reduce intraocular pressure (IOP) by different mechanisms. LP improves aqueous humor outflow and timolol reduces aqueous flow. We sought to determine whether baseline aqueous humor dynamics influenced the ocular hypotensive efficacy of either drug.
This is a retrospective investigation of data from 30 ocular hypertensive subjects in a previous, double-masked crossover fluorophotometric study. IOP (9 AM and 11:30 AM) was determined by pneumatonometry, aqueous flow and outflow facility (C) by fluorophotometry and uveoscleral outflow (Fu) by mathematical calculation using the Goldmann equation and an episcleral venous pressure of 11 mmHg. Measurements were made at baseline and at 1 and 6 weeks of treatment with timolol 0.5% twice daily or LP 0.005% once daily in the evening. Scatter plots were evaluated and linear correlations were computed where appropriate, with and without correction for baseline IOP.
At baseline, significant (p<0.05) correlations included: 1) higher IOP and lower C (r=-0.47); 2) higher IOP and higher Fu (r=0.39). The percent IOP reduction produced by LP or timolol after 1 or 6 weeks of treatment was significantly (p<0.0001) correlated with the baseline IOP (r= 0.62 to 0.66). The percent drop in IOP with LP at 1 or 6 weeks significantly (p=0.001 and p=0.032, respectively) correlated with baseline Fu (r=0.63 and r=0.42) and at 1 week significantly (p=0.007) inversely correlated with baseline C (r=-0.51). At 1 or 6 weeks, the percent IOP reductions produced by LP were significantly (p=0.001) correlated with the rise in C (r=0.62 and r=0.38). Using a multivariate analysis, the correlations between IOP reduction and either C or Fu (with a single exception) became insignificant after correcting for the confounding variable of baseline IOP. Only the positive correlation between IOP reduction and increase in C at 1 week remained significant for LP in the multivariate analysis. The ocular hypotensive efficacy of timolol did not correlate with the baseline or change in aqueous flow at either 1 or 6 weeks.
Patients with higher baseline IOPs respond better to LP or timolol than patients with lower baseline IOPs. The ocular hypotensive efficacy of timolol is not affected by baseline aqueous flow. The ocular hypotensive efficacy of LP correlated with change in C only at 1 week. No conclusion can be made concerning effects of LP or timolol on Fu as the results are inconsistent.
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