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Nathan Welch, Shane Havens, Donna Neely, Vikas Gulati; Effect of Commonly Used Topical Anesthetics on Intraocular Pressure Measurements. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1976.
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Topical anesthetics have been shown to affect episcleral venous pressure in animal models. The purpose of this study was to examine the effect of commonly used topical anesthetics on intraocular pressure (IOP) measurement.
Twenty volunteers with a normal anterior segment examination, not currently using any topical medications, and with no history of prior ocular surgery were included in the study. At baseline, IOP was measured without any topical anesthetic using rebound tonometry (RT, ICare® tonometer). Proparacaine hydrochloride, 0.5% was administered in the right eye and benoxinate hydrochloride, 0.4% (with 0.25% fluorescein sodium) in the left eye. IOP was measured with RT at 1 minute and 5 minutes after administration of topical anesthetics by a second masked observer. IOP was also measured by Goldmann applanation tonometry (GAT) by a third masked observer at 5 minutes. Central corneal thickness (CCT) was obtained with an ultrasonic pachymeter.
In proparacaine treated eyes, both the 5 min RT IOP (15.0 ± 4.2 mmHg) and 5 min GAT IOP (15.2 ± 4.6 mmHg) were significantly (ANOVA p value <0.01) lower than the baseline RT IOP (16.6 ± 4.2 mmHg). A similar trend towards slightly lower IOP at 5 minutes seen in the benoxinate treated group did not reach statistical significance (ANOVA p value = 0.11). Fifteen of 20 eyes in the proparacaine group and 12 of 20 eyes in the benoxinate group had lower RT IOP at 5 min as compared to baseline. Bland Altman plots showed good correlation between 5 min RT IOP and GAT IOP (mean difference = 0.2 ± 2.1 mmHg). A trend towards lower readings on GAT IOP (vs. RT IOP) was observed with thinner CCT. GAT IOP readings tended to be higher than RT IOP with thicker corneas (R2=0.13, p=0.13).
Topical anesthetic use was found to be associated with lower IOP readings after 5 minutes. Lowering of episcleral venous pressure is one possible explanation for the observed change. However, the exact mechanism mediating this change needs to be further evaluated.
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