Evaluation of ocular irritancy potential: intralaboratory variability and effect of dosage volume

A series of 7 compounds was evaluated for ocular irritancy potential in the rabbit eye when applied at volumes of 100 microliters (1 material) or 10 microliters (7 materials). All of the materials had been rated for ocular irritancy in previous tests and ranged in efficacy from mild to corrosive. Eyes were examined by two independent readers for up to 21 days post-dosing and evaluated by the Draize system. Only differences among rabbits were found to contribute to the observed variability of the scores obtained. Also, a dose-effect relationship was clearly discernable in terms of both duration of effect and maximal score. When these materials were tested at 10 microliters, the rank correlation of severity was not changed. Therefore, reducing the volume of test material instilled into the rabbit eye moderates the response without compromising test sensitivity.