IN-VITRO ALTERNATIVES FOR OCULAR IRRITATION

The necessity of using animals to test whether new chemicals and produ cts are eye irritants has been questioned with increasing frequency an d fervor over the last 20 years. During this time many new nonanimal m ethods have been proposed as reliable alternatives to the traditional rabbit (Draize) test. To date, however, none of these nonanimal (in vi tro) tests have become universally accepted as a complete replacement for the Draize test. To understand why a complete replacement has not been found, one has to first understand the reasonably complex structu re of the eye, the standard Draize scoring scale-which is based on a q ualitative evaluation of three different tissues-the differences betwe en human and rabbit eyes, the intrinsic variability of the animal test , and the details of the different in vitro tests that have been propo sed as replacements. The in vitro tests vary from relatively simple as says using single cells to more sophisticated assays that use discarde d animal tissue or artificially constructed human tissue. It is clear that appropriately designed in vitro tests will eventually give more u seful mechanistic information about ocular injury from which we can mo re comfortably predict the risk of human eye irritation from new produ cts and ingredients.