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E. Martin, M. A. Johnstone, A. Jamil; Aqueous Outflow Increase Resulting From Transient Blink-Induced IOP Elevation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):142.
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To observe and measure how transient blink-induced changes in intraocular pressure cause changes in aqueous flow into the aqueous and episcleral veins in normal subjects.
Research microscope (80-power magnification), micrometer scale, videography. Five eyes, 5 normal subjects, mean age 33.2 (R24-54), F/M 4/1, race C4, O1. Aqueous veins contain separate strata; the clear aqueous strata originates from Schlemm’s canal while the blood strata originates from the episcleral veins . The diameter of the aqueous strata oscillates in synchrony with the ocular pulse. Blinking occurs about every 20 seconds and induces a transient IOP increase of ~10 mm Hg. It is well-documented that the diameter of the aqueous strata increases transiently following a blink1. However, a quantitative study to document the transient blink-induced increase in aqueous strata diameter has not previously been undertaken. Twenty measurements were made of the maximum aqueous strata diameter (ASD) immediately following a blink and the measurements made again once the aqueous vein returned to their preblink appearance.
An observable increase in flow into the aqueous veins became manifest immediately following a blink. The ASD once stabilization occurred following recovery from a blink was 35.0+/- 19.6 microns (R = 0-66.2microns). Mean ASD immediately following a blink was 56.6+/- 19.2 microns (R = 0-104.7microns) representing a 62% increase. The difference between ASD immediately following a blink and ASD once stabilization occurred following recovery from the blink was significant in each subject (p=<.0001(3), .003(1), .0198(1)).
Our study describes a technique that allows direct observation and measurement of changes in the ASD in aqueous veins that result from blinking. The increased ASD is a reflection of increased blink-induced aqueous entry to the aqueous veins from SC. The physiologic blink reflex appears to induce regularly recurring transient increases in aqueous flow through the conventional outflow system.1. Ascher KW. The Aqueous Veins Vol 1. Springfield: Charles C. Thomas; 1961
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