Corneal Models for the Toxicity Testing of Drugs and Drug Releasing Materials

T he Draize rabbit eye irritation test developed in the 1940’s is even today the only eye toxicity test officially accepted in the OECD countries for regulatory purposes in the classification of slightly and moderately irritating chemicals. It is based on the subjective scoring of three tissues of the eye: the cornea, the conjunctiva and the iris. The Draize test has been widely criticized for both scientific and ethical reasons, and alternatives have been investigated for several decades. In fact, it has been estimated that more effort has been focused on finding alternatives to the Draize eye test than on all the other acute in vivo toxicity tests combined. Organotypic test models, i.e. isolated rabbit and bovine whole eyes and corneas and various kinds of cell culture techniques have been developed to replace the Draize eye test. Extensive research in the field of tissue engineering has concentrated on the development of an in vitro model for the cornea. These threedimensional corneal models were constructed by tissue engineering methods from the three corneal cell types: epithelial cells, keratocytes, and endothelial cells, and they provide a promising tool for the testing of the corneal toxicity of drugs and drug releasing materials.