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This method can be used to predict the ocular irritancy potential of chemicals, substances and mixtures.

Specifically, the intended use of the test is to identify chemicals not requiring classification and labelling as substances that can cause serious eye damage or irritation.

The test is based on a 3D corneal tissue model consisting of normal human-derived epidermal keratinocytes (cells that make up the outermost surfaces of skin) (NHEK) that are cultured at an air-liquid interface.

Relative tissue viability after exposure to a test substance is measured with a cytotoxicity assay (the MTT assay) with the outcome being used as a proxy for eye irritancy.

The method was assessed in a series of validation studies and is now the subject of OECD test guideline No 492.

The results of the validation study, the peer review of ESAC and our recommendations can be found on TSAR, the Tracking System for Alternative methods towards Regulatory acceptance.

Read more about the EpiOcular Eye Irritation Test (EIT) on TSAR

Eye irritation

[collapsed]Eye irritation in terms of this test method refers to the ability of a test substance to penetrate through the cornea and produce cell and tissue damage.

While cell damage can occur via several different mechanisms, cytotoxicity is considered an important mechanism. Indeed, when this happens in vivo the response to a chemical can range from corneal opacity, iritis, conjunctival redness and/or conjunctival chemosis.[/collapse]

EpiOcular eye irritation test

[collapsed]The EpiOcular Eye Irritation Test (EIT) is based on NHEK tissue that is cultured at an air-liquid interface (the basal region is in contact with liquid medium, while the apical side of the tissue is exposed to air).

The key feature of the model is that NHEK tissue is a kind of reconstructed human cornea-like epithelium which closely mimics various properties of the human corneal epithelium.

Following exposure to a test substance or chemical, cell viability and specifically cytotoxicity is assessed as an end-point that acts as a proxy for eye irritation or serious eye damage.[/collapse]

Animal testing replacement

[collapsed]The intended use of the test is to identify substances that do not require labelling as serious eye irritants. Thus as part of strategic combinations of several alternative in vitro methods, such as bottom-up and top-down approaches, it may be part of a solution to fully replace the use of the Draize eye irritation test that relies on testing on rabbits.

One caveat to this is that the method cannot differentiate between substances that have the potential for severe eye damage or eye irritation. This means other methods will be needed to definitively determine which category a chemical or substance should be placed in.[/collapse]

Validation study

[collapsed]The EpiOcular Eye Irritation Test (EIT) method has been the subject of numerous evaluations and (pre-) validation studies.

As part of a wider validation study led by EURL ECVAM, the method was assessed for reproducibility, transferability and predictive capacity.[/collapse]

Validation study outcomes

[collapsed]The method was used to assess 113 chemicals in three independent laboratories against a range of performance criteria.

The overall outcome indicated high reproducibility (>90%) and that the method should be regarded as scientifically validated for the identification of chemicals/substances not requiring classification for serious eye damage/eye irritation (according to UN GHS).[/collapse]

EURL ECVAM recommendations

[collapsed]Based on the outcomes of the study, the recommendation was made that the method can be used with essentially all types of chemicals/substances and can be used to identify substances not requiring classification for serious eye damage/eye irritation.

With some small reservations, the ESAC peer review agreed with this outcome. Subsequently, the EpiOcular eye irritation test was submitted for adoption to the OECD in 2014 and was accepted in 2015 as Test Guideline 492.[/collapse]