Factors affecting use of the hen's egg chorioallantoic membrane as a model for predicting eye irritation potential: I

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Abstract
The Draize rabbit eye test has been used for over 40 years to determine the eye irritation potential of materials. To minimize the use of animals in safety testing, investigators have been searching for alternatives to the Draize test. One alternative model investigated by a number of scientists is the chorioallantoic membrane (CAM), a highly vascularized membrane that forms to surround a developing chick embryo. A variety of procedures for using this model to estimate eye irritancy have been proposed in the literature. The work presented here describes how different variables affect the correlation of the CAM response to in vivo eye irritation. Variables studied include chemical structure of the test material, age of the CAM, volume of test material applied, interval between dosing and evaluating the CAM response, and the endpoint evaluated. The results show that specific chemical entities could be identified that cause false-positive responses in the CAM (i.e., the CAM is overly sensitive to these materials compared to the in vivo eye response) and that reducing dose volume or treating a younger CAM does not improve the correlation. However, it was found that the initial effect of test materials on the CAM vasculature is a suitable endpoint for differentiating irritants from nonirritants. Evaluation of hemorrhaging and hyperemia of the CAM vasculature at 30 minutes after treating the CAM is an effective procedure for reducing false-positive responses and may serve as the basis for a new assay procedure using the CAM as a model for eye irritation potential.