Reducing the number of rabbits in the Draize eye irritancy test: a statistical analysis of 155 studies conducted over 6 years.

The Draize eye irritancy test in rabbits has been the focus of recent efforts to reduce the use of live animals in toxicity testing. A suitable alternative is not yet available; therefore, we studied the adequacy of reducing the number of rabbits used per test. Data generated from 6-rabbit eye irritation tests of 155 various materials were used to determine the ability of irritation scores from all possible combinations of 5-, 4-, 3-, or 2-rabbit subsets to predict the Draize score derived from six rabbits. There are 930, 2325, 3100, and 2325 possible combinations of 155 studies for the 5-, 4-, 3-, and 2-rabbit subsets, respectively. We classify materials using a four-level adjectival rating system based on (among other factors) the Draize score. Comparisons indicated that 5-, 4-, 3-, and 2-rabbit scores were in 98, 96, 94, and 91% agreement, respectively, with the classification assigned on the basis of the 6-rabbit score. The correlation coefficients for randomly selected subsets of 5-, 4-, 3-, and 2-rabbit scores versus the Draize score for six rabbits were 0.998, 0.996, 0.992, and 0.984, respectively. This study confirms the findings of an earlier report by De Sousa et al. (1984), and indicates that a high level of accuracy can be obtained with reduced numbers of rabbits per test.

Vitreal syneresis in rhesus monkeys.

The eyes of 15 rhesus monkeys were evaluated. Various degrees of vitreal syneresis were observed in 28 of the 30 eyes. The observed vitreal structures varied from fine strands randomly spaced throughout the vitreous to thick, intertwining, fibrous networks with some clumping of the collagenous condensate at the fiber junctions. Qualitatively, the degree of syneresis was slightly more extensive in the eight older mature males than in the seven younger animals. In all animals a clear view of the fundus could be obtained with the ophthalmoscope. The vitreous structures may be one cause of variability in ocular dose-response relationships for exposure to laser radiation. The effect on retinal exposure experiments of the finer vitreal structure is considered minimal.