A rapid testing procedure to determine low levels of ocular irritation

A new and rapid method for testing low levels of ocular irritation using a balanced incomplete block design, a new grading system, and statistical analysis of the results, has been developed. Two drops (0.1 ml) of 1 of 5 ophthalmic solutions were instilled into the conjunctival sac of the right or left eye of each of 10 New Zealand white [Deb:(NZW)] rabbits hourly for 9 hr on 4 consecutive da. Before the study and before the first instillation on each day, the eyes were examined with a direct ophthalmoscope, and the reactions were graded according to a modification of the system in the illustrated Guide for Grading Eye Irritation by Hazardous Substances. The new procedure showed that 1 of the 5 solutions elicited a significantly more severe (p less than or equal to 0.05) ocular response of redness, chemosis, and discharge than did any of the other 4 solutions. Previous testing of this solution in rabbits by standard laboratory procedures and the Draize method of grading ocular irritation failed to detect these reactions.