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J. W. McLaren, L. A. Bachman, S. V. Patel; Ultraviolet and Blue Transmittance of the Feline Cornea Before and After Lamellar Keratectomy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3691.
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Does surgical reduction of corneal thickness change the transmittance characteristics of the cornea? An increase in ultraviolet transmittance could increase the hazardous exposure to the lens. In this study we measured the transmittance of the cornea to ultraviolet and blue light in vivo in cats before and after lamellar keratectomy.
Corneal transmittance was measured in unoperated corneas of 9 cats by using a method described earlier (McLaren and Brubaker, Curr Eye Res (1996) 15:411-421). Briefly, fluorescein and the blue fluorophore PTS1 (Sigma-Aldrich, St. Louis, MO) were mixed with sodium hyaluronate 1%, each to a final concentration of 1 µM. Aqueous humor was drained and replaced with this mixture. Within 10 minutes, excitation and emission spectra of both dyes were measured by using a custom scanning spectrofluorometer. The same spectra were measured in a quartz cuvette and transmittance at each wavelength between 250 nm and 500 nm (5-nm steps) was calculated from the relative fluorescence in the anterior chamber to that in the cuvette. Corneas of 4 of the cats then had an anterior lamellar keratectomy. Transmittance measurements were repeated at 1, 3, and 6 months after keratectomy. Central corneal thickness was measured by ultrasonic pachymetry (DGH Technology, Inc. Exton, PA). Mean transmittance between 270 and 300 nm, and between 400 and 500 nm as well as the wavelength at 50% transmittance after keratectomy were compared to those before keratectomy by using generalized estimating equation models with Bonferroni correction for 3 comparisons.
Mean central corneal thickness decreased from 600 ± 38 µm before to 292 ± 91 µm, 333 ± 86 µm, and 352 ± 105 µm at 1, 3, and 6 months respectively after keratectomy (± SD, p<0.003). Before keratectomy, mean transmittance was 94.0 ± 2.7% and 2.4 ± 1.2% between 400 and 500 nm and between 270 and 300 nm respectively. The mean wavelength of 50% transmittance was 328 ± 1.1 nm. In the long wavelength band, transmittance decreased to 88.4 ± 1.7% (p=0.003) at 1 month but returned to preoperative transmittance at 6 months (96.2 ± 1.0%, p=0.4). Transmittance below 300 nm was unchanged at 6 months (2.5 ± 1.3%, p>0.3, minimum detectable difference = 2.7%, =0.05/3, β=0.2). The 50% transmittance wavelength decreased to 324 ± 3.9 nm at 6 months (p=0.015).
Reducing stromal thickness by 43% does not increase corneal transmittance below 300 nm by more than 2.7% transmittance. Transmittance to blue light transiently decreases, but returns to pre-op transmittance by 3 months.
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