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V. Gulati, S. Fan, S. L. Galata, G. Zhan, M. A. Maslonka, C. B. Camras, C. B. Toris; Effects of Latanoprost on Daytime and Nighttime Aqueous Humor Dynamics. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2006.
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This study investigates the day and night effects of once daily dosing of latanoprost (0.005%) on intraocular pressure (IOP), central cornea thickness (CCT), blood pressure and aqueous humor dynamics.
Thirty ocular hypertensive (OHT) volunteers were enrolled in this double-masked prospective study. After a 6-week washout of current ocular drugs, subjects underwent study measurements during the day and night at baseline and after 2 weeks of nightly latanoprost use. Study measurements included IOP by pneumatonometer, blood pressure by sphygmomanometry, CCT and anterior chamber depth by pachymetry, aqueous flow by fluorophotometry and outflow facility by fluorophotometry and tonography. Episcleral venous pressure was measured during the day and calculated for night using published formulas. Uveoscleral outflow was calculated by using Goldmann’s equation.
Compared to daytime, nighttime changes in untreated OHT eyes include a reduction in uveoscleral outflow and aqueous flow and an increase in CCT. Compared to baseline, latanoprost significantly lowered IOP at all times measured during the day (9 AM and noon) and night (10 PM, midnight, 2 AM, 5 AM). The mean diurnal IOP decrease was 19%. At night, seated IOP decreased by 13% and supine IOP decreased by 10%. There was no significant effect of latanoprost on episcleral venous pressure, aqueous flow and outflow facility at any time. With latanoprost use there was a significant increase in daytime uveoscleral outflow calculated with tonographic data (1.17 µl/min, p=0.003) or fluorophotometric data (0.55 µl/min, p=0.025). Latanoprost also increased the tonographically calculated uveoscleral outflow (0.40µl/min, p=0.11) at night but the change did not reach statistical significance.
Latanoprost effectively lowers IOP during the day and night with once nightly administration. The IOP reduction can be explained by an increase in uveoscleral outflow. The daytime effects of latanoprost on IOP and uveoscleral outflow are more pronounced than the nighttime effects. The nighttime improvement in uveoscleral outflow with latanoprost is partly negated by the spontaneous physiological nocturnal reduction in uveoscleral outflow seen at baseline.
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