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M. Malihi, J. W. McLaren, A. J. Sit; Episcleral Venous Pressure Measurement by Computerized Venomanometry, With and Without Topical Anesthesia. Invest. Ophthalmol. Vis. Sci. 2010;51(13):188.
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© ARVO (1962-2015); The Authors (2016-present)
: Previous research has shown that topical anesthesia reduces episcleral venous pressure (EVP) in rabbits. If topical anesthesia also reduces EVP in humans, it has important implications for the measurement of aqueous humor dynamics. The purpose of our study was to determine if EVP in humans is reduced by topical anesthetics.
EVP in thirteen healthy, low myopic (less than -4 D), regular soft contact lens wearers was measured by using a new, custom, computerized episcleral venomanometer. This system uses the pressure chamber technique to measure the pressure required to partially collapse an episcleral vein. The pressure in the compression membrane is increased and monitored by computer and synchronized with a video sequence of the vein. The pressures required to compress the episcleral vein to 90% and 50% of its baseline patency as viewed in the video sequence, were recorded as estimates of episcleral venous pressure (EVP90 and EVP50 ,respectively). EVP measurements were obtained before anesthetic in both eyes. One eye of each subject was then randomly selected to receive topical proparacaine 0.5% ("Treatment") while the contralateral eye did not receive any eye drops ("Contralateral"). EVP measurements were obtained five minutes after anesthetic in the Treatment eyes, and ten minutes after anesthetic in the Contralateral eyes. EVP measurements with and without anesthetic were compared by using paired t-test with statistical significance assumed for P<0.05.
The mean EVP90 and EVP50 before anesthetic were 7.5±2.5 and 10.2±2.5 mmHg, respectively, in the Treatment eyes and 7.5±2.3 and 10.5±2.4 mmHg, respectively, in the Contralateral eyes (± SD). Five minutes after instillation of anesthetic, there was no significant change of EVP in the Treatment eyes: EVP90 and EVP50 were 7.2 ± 2.4 mmHg and 9.5 ± 2.1 mmHg, respectively (p>0.05). Ten minutes after instillation of anesthetic, EVP90 and EVP50 in the Contralateral eyes decreased to 6.4±1.9 and 9.1±2.2 mmHg, respectively (P<0.05).
EVP is reduced 10 minutes after topical anesthetic is instilled in the contralateral eye, suggesting a central vasogenic effect. A direct effect may also occur but was not significant after 5 minutes. Episcleral venous pressure plays a major role in determining intraocular pressure, and its sensitivity to topical anesthetics must be considered when it is measured in studies of aqueous humor dynamics or clinical practice.
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