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An objective procedure for quantitating eye irritation based upon changes of corneal thickness
H E Kennah1, S Hignet, P E Laux
1Department of Toxicology, PPG Industries Inc., Pittsburgh, Pennsylvania 15238.
Summary
Corneal thickness changes measured by pachometry offer a reproducible, objective alternative to the subjective Draize test for quantifying eye irritation in rabbits. This method provides sensitive detection of healing and a reliable ranking of chemical irritancy.
Area of Science:
- Ophthalmology
- Toxicology
- Animal Welfare Science
Background:
- The Draize test, a long-standing method for assessing eye irritation, faces criticism due to animal welfare concerns and subjective scoring.
- There is a need for objective, reproducible methods to quantify ocular irritation and reduce reliance on animal testing.
Purpose of the Study:
- To evaluate changes in corneal thickness using slit-lamp pachometry as a replacement for the subjective Draize scoring procedure.
- To establish a quantitative method for assessing ocular irritation and ranking chemical irritancy.
Main Methods:
- Twenty-four chemicals were applied to rabbit eyes, with irritation assessed via Draize scoring and corneal thickness measurements using pachometry.
- Correlation analysis was performed between Draize scores and corneal thickness changes.
Main Results:
- Corneal thickness measurements showed less variation and higher sensitivity in detecting healing reactions compared to Draize scoring.
- A significant linear correlation (r=0.86) was found between Draize scores and corneal thickness changes.
- An ocular irritation ranking system based on corneal swelling was proposed, with surfactants > alcohols > ketones/acetates > aromatics.
Conclusions:
- Quantifying ocular irritation via corneal thickness changes provides objective, numerical data, reducing subjective bias and variability.
- Pachometry offers a sensitive and reproducible method for evaluating ocular irritancy and ranking chemical safety.