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Currently, the OECD has adopted three defined approaches (DAs) for eye hazard identification of non-surfactant liquids and solids (TG467) according to the three UN GHS categories (Cat.1, Cat.2, No Cat.). We are now expanding the applicability domain with a new DA for chemicals having surfactant (SF) properties (DASF). It is based on a combination of RhCE test methods (OECD TG492: EpiOcular™ EIT or SkinEthic™ HCE EIT) and a modification of the Short Time Exposure (STE, TG491) method. The aim of the current study was to compare the performance of the DASF with the performance of other NAMs currently included in the OECD TGs and with the classification based on the Draize eye test to identify potential additional DAs. The minimum performance criteria (75% Cat.1, 50% Cat.2, 70% No Cat.) used for the adoption of the DAs currently included in OECD TG467 were used for this purpose. The DASF identified 90.9% of Cat. 1 (N=23), 77.8% of Cat. 2 (N=9) and 76.0% of No Cat. (N=17) surfactants, meeting the minimum performance criteria. Some of the NAMs that are currently included in the OECD TGs seem promising methods to be part of a DA to identify Cat. 1 or No Cat. for eye hazard assessment of surfactants. However, the number of surfactants that have been tested to evaluate reliability and relevance was often too small. To date, the DASF is the only DA that has evaluated a sufficiently large number of surfactants and whose performance met the OECD acceptance criteria.

The Short Time Exposure (STE) test evaluates eye irritation potential using a 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. MTT assays may underpredict results for some substances that directly reduce MTT (i.e., MTT reducers) or interfere with absorbance because of their strong color (i.e., strongly colored substances). Based on previous research, we selected 25 substances as MTT reducers. Of these, 13 were expected to be MTT reducers at 5% dilution (5% MTT reducers) of the STE test condition. These 13 substances were then tested to determine whether the results were interfered from direct MTT reduction. Those 5% MTT reducers that were classified as irritants based on in vivo data were identified as irritants by the STE test. In addition, the low cell viability results at 5% dilution suggested that direct MTT reduction had not occurred. Next, the remaining 5% MTT reducers that were classified as non-irritants based on in vivo data were identified as non-irritants by the STE test. We then examined two strongly colored substances. One was classified as an irritant based on in vivo data and was confirmed as an irritant by the STE test. The other was classified as a non-irritant by the STE test. This was further evaluated using a medium that did not contain MTT; the result indicated that it was a non-irritant correctly. In conclusion, the STE test is useful for evaluating eye irritation potential without the drawback of underprediction for MTT reducers and strongly colored substances.