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Mehrdad Malihi, Jay W. McLaren, Arthur J. Sit; Effects of Topical Anesthesia on Episcleral Venous Pressure Measurement. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1509.
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Episcleral venous pressure (EVP) is important for understanding aqueous humor dynamics, and its sensitivity to topical anesthetics must be considered when it is measured. Animal studies indicate that topical anesthetics can reduce EVP. As well, in a previous preliminary investigation, we found a possible delayed reduction of EVP after instilling topical anesthetic in the contralateral eye, but no effect in the ipsilateral eye. In this study, we further investigated the effects of topical anesthetics on EVP.
EVP was measured in 30 eyes of 15 healthy, low myopic (< -4D), regular soft contact lens wearers aged 20-37 years (mean 27.2 ± 7.9) by using a computerized episcleral venomanometer. An inflatable chamber was applied to the sclera and the vein was monitored by video recording while the chamber was inflated. Pressures that compressed an episcleral vein to various degrees of compression were recorded as venous pressure. One eye was randomly selected to receive topical proparacaine 0.5%. EVP was measured in both eyes at baseline, and again 5 and 10 minutes after anesthetic. These measurements were repeated on a second day, with anesthetic instilled in the other eye. EVP at 5 and 10 minutes after anesthetic was compared to EVP before anesthetic by using paired t-tests and generalized estimating equation models.
EVP did not change in the anesthetized eye or the contralateral eye after instillation of proparacaine in one eye (all P-values >0.1) (table 1). The minimum detectable difference ranged from 1.4 mmHg to 1.9 mmHg (α=0.05, β=0.2).
Contrary to our earlier pilot study, EVP does not change after topical anesthesia. The previous result may have been due to random variation. The difference in results for our study compared with animal studies may be due to inadequate penetration through the conjunctiva, which is typically removed in animal studies. Our results indicate that EVP can be reliably measured non-invasively in humans after topical anesthesia.
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