Reducing the number of rabbits in the low-volume eye test

By Bruner, L.H. - Parker, R.D. - Bruce, R.D.

Although the Draize eye irritation test has provided important and useful information for eye safety assessments, considerable effort has been directed toward refining the assay procedure, reducing the number of animals used, and replacing this assay with alternative methods. The low-volume eye test (LVET) is a refinement of the Draize eye irritation test that uses 1/10 the volume of test substance placed directly on the cornea. The level and duration of eye irritation in the LVET are less than those in the Draize procedure, which means that it is a less stressful test. Furthermore, LVETs are more predictive of human response. Statistical studies have been conducted to determine the effects of reducing the number of animals used in the Draize test. These results suggested that a three-animal test would provide essentially the same information as the six-animal test. A similar analysis has not been performed on results from the LVET. Accordingly, the present study was undertaken to evaluate previously existing LVET data to determine if the number of animals used in a LVET can be decreased as has been shown for the Draize test. The results of the analysis are consistent with the findings of earlier evaluations of classical Draize data. Three-animal subsets from 119 six-animal LVETs provided the correct classification greater than 92% of the time for three different classification schemes. Furthermore, the discrepancies between the three-animal subsets and the six-animal maximum average score tended to be smaller than those observed for the Draize test. The analysis suggests that a three-animal LVET will provide an eye irritation classification similar to that obtained from a six-animal study.