A simplified index to quantify the irritation/corrosion potential of chemicals - Part II: Eye

Eye irritation is a key human health endpoint assessed by in vitro and in vivo methods. One of the commonly used scoring methods to quantify the eye irritation potential of chemicals is the Modified Maximum Average Score (MMAS). It is dependent on the eye irritation effects (e.g. corneal opacity) originally proposed by Draize and then partially adopted by the OECD TG 405. These scores are not always fully reported in regulatory dossiers and lead to several drawbacks, 1) the difficulty to translate MMAS into a classification within the existing EU CLP/UN GHS criteria, 2) the absence of corrosion (serious eye damage), and 3) the dependency on input parameters which are usually not required under the OECD TGs (e.g. eye surface area). This study determined if classification can be driven by a maximum of two observed effects thereby simplifying the scoring calculation. The Simplified Irritation Index (SII_EYE), based only on corneal opacity and conjunctival redness, was developed using validated studies representing multiple chemical groups. A correlation was observed between the MMAS and the SII_EYE allowing harmonisation of the classification for the existing data. This index proved to be useful in the development of in silico model.