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M. A. Johnstone, E. Martin, A. Jamil; Latanoprost Instillation Results in a Rapid Directly Measurable Increase in Conventional Aqueous Outflow in Normal Subjects. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1553. doi: https://doi.org/.
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To determine whether instillation of latanoprost results in a visible increase in aqueous flow through the trabecular meshwork and SC to the aqueous veins in normal subjects.
Research microscope (80-power magnification), micrometer scale, videography. Five eyes, 5 normal subjects, mean age 36.6 (R 22-64), F/M 4/1, race C4, O1. The following intervals in minutes were recorded: 1,2,3,4,5,10,20,30,45,60,90,120. Aqueous veins contain separate strata; the clear aqueous strata originate from the AC while the blood strata originate from the episcleral veins1. The diameter of the aqueous strata oscillates in synchrony with the ocular pulse1. Ten measurements were made of the maximum aqueous strata diameter during systole (ASD) before and 60 minutes after latanoprost instillation. In 2 subjects (S1, S2), velocity of aqueous flow was measured.
Timing of the first observable increase in flow into the aqueous veins was manifest as increased amplitude and velocity of the oscillating pulse wave of the aqueous strata. First appearance of flow increase ranged from 10 to 30 minutes and was marked at 60 minutes. Before latanoprost mean ASD was 30.3 ± 6.5 microns (R = 24.0-37.7 µ) while at 60 minutes mean ASD was 60.5 ± 19.2 µ (R = 34.4-82.8 µ) a 100 % mean ASD increase. The difference between pre-latanoprost and 60 minute post-latanoprost ASD was significant in each subject (p<.0001). Maximum increase in velocity of aqueous flow at 60 minutes was: (S1 68 %), (S2 37 %). Mean IOP before latanoprost was 13.4 mm Hg (R 11-16). Lowest IOP’s were attained in the 60-120 minute time interval. The mean of the lowest pressure readings was 9.4 mm Hg (R 8-12), representing a 29.9% mean IOP decrease.
Our pilot study describes a new technique that allows direct measurement of the quantity and character of drug-induced aqueous flow through the conventional outflow system. These direct measurements identify a large latanoprost-induced increase in aqueous flow that passes through the trabecular meshwork and SC to then enter the visible aqueous veins. Two such aqueous veins can carry all of aqueous outflow1. Our findings are thus consistent with the conclusion that an important mechanism of latanoprost action involves an increase in conventional aqueous outflow that precedes a decrease in IOP.1. Ascher KW. The Aqueous Veins. Vol. 1. Springfield: Charles C. Thomas; 1961.
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