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Changing concepts of ocular irritation evaluation: pitfalls and progress
Summary
Modifying ocular irritation tests by reducing dosage and animal numbers lowers response severity without compromising predictability. However, skin irritation severity does not reliably predict eye irritation potential.
Area of Science:
- Toxicology
- Ocular Irritation Testing
- Animal Welfare
Background:
- Existing ocular irritation tests often use significant animal numbers and can cause severe responses.
- There is a need to refine these tests to reduce animal use and distress while maintaining predictive accuracy.
Purpose of the Study:
- To evaluate modifications of ocular test protocols for reduced animal use and severity.
- To assess the impact of dose reduction and application site on ocular responses.
- To determine if dermal irritation predicts ocular irritation potential.
Main Methods:
- Reduced ocular test dosage from 100 to 10 microliters.
- Compared direct corneal application versus conjunctival cul-de-sac application.
- Retrospectively analyzed 60 known severe skin irritants for ocular irritation potential.
Main Results:
- Reducing dose to 10 microliters decreased response severity without altering compound rank order.
- Rabbit population variability is a major source of score inconsistency; animal numbers can be adjusted for desired accuracy.
- Direct corneal application enhanced corneal response but not conjunctival response.
- Severe skin irritants were not consistently severe ocular irritants (39/60 severe, 15/60 mild/non-irritant).
Conclusions:
- Ocular irritation test protocols can be modified for reduced animal numbers and less severe conditions with minimal impact on predictability.
- Dermal irritation, as currently tested, is not a reliable predictor of ocular irritation.