The Agarose Overlay Method as a Screening Approach for Ocular Irritancy: Application to Cosmetic Products

Abstract

The in vitro agarose overlay method was investigated as an alternative to the Draize eye irritation test for the evaluation of the ocular irritancy of cosmetic products.

Modifications to the original protocol include the definition of an area of lysis (expressed as a weighty)/toxicity relationship for each product by a planimetric method and the creation of an agarose classification.

56 different cosmetic formulations, including emulsions, gels, lotions and tonics, were evaluated using this modified test, and the results were correlated with in vivo Draize data. Four different agarose classes were delimited: non-irritant; minimally irritant; mildly irritant; and irritant; corresponding respectively to the following scoring scales (x 10 ⁴g): 0; 0 <x<200; 200≤ x <450 and ≥ 450.

A high correlation between the agarose overlay method and the Draize test was observed when taking into account two classes: non-irritant (non-irritant, minimally irritant) and irritant (mildly irritant, moderately irritant [Draize] or irritant [agarose]) as shown by an 86% concordance value. In this study, the sensitivity was 92% (11–12 irritants were predicted by the agarose diffusion method) and the specificity was 84%. The overestimation error of 16% suggests that the agarose overlay method might be slightly more sensitive than the Draize eye test.

When applying the kappa test, the agarose overlay method reached a 64% coefficient, attesting that the good correlation with the Draize test was not due to chance. In relation to the Landis & Koch classification, this percentage places the agarose overlay method in the “good concordance” class.

Based on these results, the use of the agarose overlay method for screening the ocular irritation potential for the cosmetics industry can be considered to be a very interesting alternative to be included in a battery of tests.