This test is performed according to the Organization for Economic Co-operation and Development (OECD) test guideline number 492 and allows for proper labeling of the test compound or xenobiotic according to United Nations Globally Harmonized System (UN GHS) Classification and Labelling of Chemicals.1
Historically, ocular irritation was performed on rabbits using the Draize Eye Test.2 However, three-dimensional human corneal tissue equivalents have been developed and validated as replacements for the Draize test. These 3D tissues are nonkeratinized, corneal epithelia grown from normal human keratinocytes and are extremely similar to native human cornea, both metabolically and morphologically. In addition, the apical surface is direct contact with the air (tissue is fed basally) allowing for testing of almost all types materials, such as gels, creams liquids, and powders, regardless of aqueous solubility.
In this assay, MatTek EpiOcular™ tissues are exposed on the apical surface to neat (undiluted) test chemical for either 30 minutes (liquid test chemicals) or 6 hours (solid test chemicals) and the viability of the tissue is then determined via the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. This data is then normalized to the negative control and ocular irritation is determined based on the viability using the following table:
|Mean Tissue Viability||In Vivo Prediction|
|≤ 60%||Irritant (Category 1/2)|
|> 60%||Non-Irritant (No Category)|
Additionally, the protocol can be adapted in order to assess irritation potency (mild, moderate, severe etc.) of test chemicals by determining the ET50 over a 6 hour exposure period.