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M. Johnstone, E. Martin, A. Jamil; Travoprost Instillation Results in a Rapid Directly Observable Increase in Conventional Aqueous Outflow in Normal Subjects. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3291. doi: https://doi.org/.
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To determine whether instillation of travoprost results in a visible increase in conventional aqueous flow to the aqueous veins in normal subjects.
Research microscope (80-power magnification), micrometer scale, videography. 5 eyes, 5 subjects, mean age 36.8 (R 22-65), F/M 3/2, race C4, O1. The following intervals in minutes were recorded: (10,20,30,60,90,120). 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 travoprost instillation. In one subject (S4) 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 was seen at between 30 and 60 minutes. Before travoprost mean ASD was 24.8 ± 6.1 microns (R = 0.0-45.2 µ) while at 60 minutes mean ASD was 53.8 ± 8.0µ (R = 17.2-79.1 µ) a 100 % mean ASD increase. The difference between pre-travoprost and 60 minute post-travoprost ASD was significant in 4 out of 5 subjects (p<.0001). Velocity of flow in S4 before travaprost was 0.99 ± .02 mm/sec and after travaprost 1.29 ± 0.05 mm/sec, representing a velocity change of 29 %. Mean IOP before travoprost was 16.8 mm Hg (R 13-22). Lowest IOP’s were attained in the 30-120 minute time interval. The mean of the lowest pressure readings was 12 mm Hg (R 9-15), representing a 28.6% mean IOP decrease.
We describe a technique that allows direct observation and measurement of drug-induced aqueous flow through the conventional outflow system. Travatan induces an increase in aqueous flow through the conventional aqueous outflow system to the visible aqueous veins. Two aqueous veins can carry all of aqueous outflow1. We conclude that an important mechanism of travoprost 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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