The Organization for Economic Co-Operation and Development (OECD) has prescribed the use of a weight-of-evidence (WoE) analysis, integrated with a sequential testing strategy, for the classification of acute eye hazards. The October 2017 revision to the Health Effects Test Guideline No. 405 outlines a stepwise strategy that includes Step 6, “Perform validated and accepted in vitro or ex vivo ocular test(s),” specifying only four possible assays: three tests designed to identify severe eye irritation/ corrosion (GHS Category 1) and one test to identify non-irritants (GHS No Category), the top-down and bottom-up approaches, respectively.
Currently, a definitive GHS Category 2 (eye irritant) classification is not achievable using any one alternative assay. Our approach utilizes the following validated alternative assays integrated to provide confident assessment of ocular irritation:
- EpiOcular™ Eye Irritation Test; EIT (OECD 492) ), Reconstructed human Cornea-like Epithelium (RhCE) test method, is a bottom-up test, useful in identifying test materials that cause no irritative effects or No Category, but this assay effective use in identifying serious eye damage, and corrosion.
- Conversely, the top-down alternative Bovine Corneal Opacity and Permeability (BCOP) Test (OECD 437), is used for identifying Category 1 effects (serious eye damage/corrosion).
By using a dual-assay/approach system – the combination of the EIT and BCOP test – we have determined, with a high degree of accuracy, GHS Acute Eye Hazard Category 2 chemicals that cause reversible eye irritation. When a BCOP test rules out GHS Category 1 and the EIT rules out GHS No Category, analysis of these results indicates the only other possible designation – Category 2. Per GHS, Category 2 classification defaults to Category 2A, because differentiation between Category 2A and 2B cannot be made.