Measurement of corneal epithelial healing rates and corneal thickness for evaluation of ocular toxicity of chemical substances

The epithelial cells bordering a corneal epithelial wound normally slide across the denuded area to close the wound. This reepithelialization generally occurs at a rate of 0.80 to 1.00 mm2/hr in the rabbit. The cornea also swells after wounding and then returns to normal thickness during the healing process. Because this is a predictable process, it is proposed that measurement of corneal healing rate and corneal thickness be used in the evaluation of potential eye irritants. It is shown that several substances, including methylene blue, isopropanol, and benzalkonium chloride, reduce the healing rate of a standardized, 6-mm diameter corneal epithelial wound as compared to a paired, untreated control. Heptanol and isopropanol cause the wounded cornea to swell to a greater thickness and delay the return to normal thickness. Thus, it is clear that toxic substances can inhibit corneal epithelial healing. Measurement of reepithelialization rate and corneal thickness yield quantitative, statistical data that can be used in addition to standard methods in the testing of chemical substances for ocular toxicity.