Measurement of transmission of ultraviolet and visible light in the living rabbit cornea

Corneal transmittance in pigmented rabbits was measured at ultraviolet and visible wavelengths from the ratio of fluorescence of dyes in the anterior chamber to fluorescence of the same dyes in a quartz cuvette. Aqueous humor was drained through a limbal incision and the anterior chamber was reformed with a mixture of a viscoelastic material and a fluorophore (fluorescein, O-methyl pyranine, or sulforhodamine B). Excitation spectra, emission spectra, or both were measured in the anterior chamber with a new scanning ocular fluorophotometer, at wavelengths between 250 nm and 700 nm. Fluorescence spectra were also measured from the same fluorophore in a quartz cuvette. External transmittance of the cornea was calculated at each wavelength from the ratio of fluorescence in the anterior chamber to fluorescence in the cuvette. Transmittance was 93% ± 1.4% (mean ± SD, n = 8 rabbits) at 500 nm and was 89% to 93% between 370 nm and 500 nm. Transmittance decreased to 82% ± 5.7% at 350 nm, to 50% ± 5.9% at 310 nm, and to less than 2% at 290 nm. Between 370 nm and 500 nm, the wavelength range most frequently used in fluorophotometry, average transmittance varied by less than 5%. These results suggest that fluorescence measured at two or more wavelengths within this spectrum needs little if any correction for differential attenuation by the cornea. At wavelengths shorter than 370 nm, measurements should be corrected. This technique provides a simple and minimally invasive means of studying visible and ultraviolet transparency of the cornea in the living eye.