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HS Greenman, LW Herndon, DL Epstein, SS Stinnett, P Challa; The Effects of Drying on Central Corneal Thickness . Invest. Ophthalmol. Vis. Sci. 2002;43(13):274.
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Purpose: To determine how quickly corneal drying occurs after instillation of proparacaine and elevation of the eyelid. Methods: Twenty-four subjects (48 eyes) with normal corneas were recruited from the Duke Eye Center. After obtaining informed consent for the study, a drop of proparacaine was placed in both eyes. The subjects were told to fixate with both eyes on a red bottle top or mirror directly in front of them. Next, three baseline measurements were made by centering the ultrasound pachymetry tip (Pachette, DGH Technology Inc.) over the center of the pupil. The right upper eyelid was then held open by the researcher's hand and three readings were taken every 15 seconds for one minute. Ambient temperature was around 72 degrees Fahrenheit with standard central air-conditioning. This process was then repeated for the left eye after completion of the right. Results: On analyzing each eye separately, statistically significant thinning(p<.01) was seen from 15 seconds as assessed by the Wilcoxian rank sum and student t-tests. The left eyes were found to have thinner CCTs throughout all time periods except for the last period(table 3). In addition, as the corneal surface dried, it became sticky and there was some epithelial irregularity over the area; however, the epithelium was grossly intact without any of the subjects complaining of post-experimental pain. Conclusion: There was significant corneal thinning within 15 seconds after instillation of topical proparacaine as compared to baseline. The thinner CCTs seen in the left eyes at baseline may be explained by exposure incurred while the right eyes were being tested. Much of the thinning was probably due to evaporation of the water component from the stroma and epithelium since the normal tear film is only 7.4um and decreases to 2.6um with the addition of proparacaine. Eyes being measured for pachymetery and undergoing procedures such as Lasik should not be left exposed after proparacaine instillation for more than 15 seconds without rehydration. Patients with glaucoma should have their IOPs checked soon after receiving topical anesthetics or may have artificially low pressures secondary to corneal thinning from exposure. View OriginalDownload SlideView OriginalDownload Slide
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