Scoring for eye irritation tests

Scoring of the rabbit eye test and the resulting evaluation and classification should provide useful information about the likelihood that a test material may cause injury on contact with the human eye. When an animal test is necessary, a rabbit eye test based on the following characteristics is proposed for deriving the maximum information from the fewest animals. The ocular effects of interest should include corneal opacity, iritis and conjunctival redness. Animals should be scored for each ocular effect at 24, 48 and 72 hr after the test substance is administered. If an animal is negative at all three scoring times, it can be removed from the test at 72 hr. If it shows a positive effect at a scoring time but the lesion clears at 72 hr, it can be removed at 72 hr. If it shows a positive effect that does not clear at 72 hr, it should be scored again on day 7 when the test ends. However, if an animal shows severe effects at one or more scoring times, it can be removed from the test at 72 hr. An animal is positive if any one of the following criteria is observed at 24, 48 or 72 hr: corneal opacity of 1 or above, or conjunctival redness of 2 or above. Severe ocular effects (noted at 24, 48 or 72 hr) that may endanger sight deserve special recognition for the classification of chemicals and include corneal opacity of 3 or above, or iritis of 2. This proposal is consistent with the opinions of the majority of respondents who attended the Workshop on Updating Eye Irritation Test Methods, Proposals for Regulatory Consensus. The most notable exception was the suggestion by respondents to add conjunctival chemosis as one of the scoring parameters.