The standard “OECD 492B Reconstituted human corneal-like epithelium (RhCE) test method for eye hazard identification”, published under the OECD guidelines on responsible business conduct for multinational enterprises (OECD guidelines), describes an in vitro procedure that allows the self-identification of chemicals (substances and mixtures) according to the UN GHS ocular hazard categories of no classification (Cat no Cat), requiring classification for eye irritation (Cat 2) and requiring classification for serious eye damage (Cat 1).
-test-yontemi.jpg "OECD 492B Test Method for Reconstructed Human Corneal-Like Epithelium (RhCE) for Eye Hazard Identification")
This procedure utilizes reconstructed human corneal-like epithelium (RhCE) that closely mimics the histological, morphological, biochemical, and physiological characteristics of the human corneal epithelium. The assay evaluates the ability of a test chemical to induce cytotoxicity in a human corneal-like epithelium (RhCE) tissue construct as measured by the MTT assay. The MTT assay is a colorimetric assay method for evaluating cell metabolic activity.
Human corneal-like epithelial (RhCE) tissue viability after exposure to a test chemical is measured by the enzymatic conversion of the vital dye MTT by living cells of the tissue to a blue MTT formazan salt, which is measured quantitatively after removal from the tissues. Cytotoxicity is measured at different time points of exposure.
The viability of human corneal-like epithelial (RhCE) tissue is determined by comparison with tissues treated with a negative control substance (percent viability) and is then used to estimate the eye hazard potential of the test chemical. Chemicals that do not require classification and labeling according to UN GHS are defined as those that do not reduce tissue viability below a certain threshold (i.e., tissue viability of at least 2 percent for UN GHS uncategorized).
The test method described in the OECD 492B standard is the first single non-animal eye irritant test method used to distinguish between GHS Category 1, Category 2 and uncategorized substances and mixtures. Until recently, the determination of GHS Category 2 eye irritants was based on a weight of evidence approach due to the inability of a single in vitro test to distinguish between Category 1, Category 2 and uncategorized test materials. With the approval of the OECD 492B test guideline, it is now possible to determine these classifications.
Test substances are classified for eye irritation hazards under the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS) into the following categories:
Currently, human corneal epithelial tissues are treated with test substances according to a time-to-toxicity protocol. Since corneal cell damage and loss of viability are highly correlated with adverse effects on corneal function and visual acuity, the viability of HCE tissues is measured after exposure to the test substance using the MTT reduction viability endpoint.
The prediction model for the UN GHS categorization is as follows:
Many manufacturers use the OECD TG 492B standard for hazard identification and labelling purposes to comply with a range of regulatory requirements.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, it also provides testing services defined in the standard “OECD 492B Reconstructed human corneal epithelium (RhCE) test method for eye hazard identification” with its trained and expert staff and advanced technological equipment.
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