Bovine corneal opacity and permeability test: an in vitro assay of ocular irritancy

Most of the published in vitro tests of ocular irritancy investigate a single parameter, generally cytotoxicity, using different cell types in culture. Although good correlations with in vivo data have been reported by some investigators, many of these studies examined only limited classes of products, mainly surfactants and cosmetic ingredients. To predict the irritant potential of compounds in development and process intermediates (which include a wide variety of chemical classes with variable physical characteristics), an assay which would allow great flexibility was needed. A recently published model of corneal opacity was appropriate for this purpose and therefore investigated. The method was substantially modified and extended to study, in the same assay, two important components of irritation, i.e., opacity and permeability. For opacity alone, values obtained for 44 common chemicals showed a correlation of r = 0.73 with published in vivo data. However, compounds like sodium lauryl sulfate and some medium-chain alcohols gave false-negative results, apparently because they produced destruction of corneal epithelium. Such an effect was quantified by the measure of corneal permeability to fluorescein, and changes observed were found to be consistent with the known irritant potential of the compounds. In combination, the measurement of these two endpoints thus appeared to be sufficient to accurately predict ocular irritancy. This was further verified with 15 process intermediates. In short, the bovine corneal opacity and permeability assay allows investigation of two important components of eye irritation, in a one-day experiment, using an ocular tissue. It represents a useful approach to assess ocular irritation at least for our needs.