Both the United Nations Globally Harmonised System (GHS) of Classification and CLP (Classification, Labelling and Packaging) Regulation 1272/2008 require categorisation of substances that pose a hazard for eye irritation and/or serious eye damage. Animal-based models such as the Draize test were once the standard, but as animal testing bans reach across more countries within the cosmetics and personal care industries, in vitro methods are coming to the forefront of modern ocular safety testing.
The GHS has three categorisations for ocular risk:
- No category – No ocular irritation or eye damage risk
- Category 1 – Serious eye damage / irreversible effects on the eye
- Category 2 – Eye irritation with reversible adverse effects (category 2 can be further sub-categorised into 2A and 2B depending on the time of initiation of the effects)
Two in vitro methods that are especially effective are the Eye Irritation Test (EIT) assay and the Short Time Exposure (STE) assay.
If the substance is not expected to be an eye irritant then a ‘Bottom-Up’ approach can be used, and the substance is first tested in the EIT. If the substance is classified as negative in this assay then no further testing is required and the substance is categorised as No Category according to the GHS classification system. If the EIT results are positive, the chemical will then proceed to the STE assay to test for ocular corrosion potential.
A ‘Top-Down’ approach is used if the substance is expected to have high eye irritation or corrosion potential, or is positive in the EIT. Using this approach the substance is assessed in the STE assay. If the results of the STE assay are positive, the substance is GHS Category 1 and requires no further testing. If the STE assay results are negative the substance can be classified as UN GHS No Category, however, a follow-up in the EIT may be prudent to confirm the absence of any mild irritation. If the substance is both ‘Unable to ID’ in the STE assay and positive in the EIT then the substance is UN GHS Category 2 and further testing may be required to determine if the substance is classified as either Category 2A or 2B.
If a more precise evaluation of ocular irritation is needed, a potency assessment is available that categorises test materials into one of the following categories: Non/minimal, mild, moderate, severe/extreme. While this method has not been evaluated by the OECD, it has been shown to be a reliable non-animal replacement for the Draize test. This can be especially useful if a finished product isn’t subjected to OECD regulations, but would benefit from verification and communication of non-irritating potential.
The following flow chart illustrates the differences between the Top-Down and Bottom-Up approaches to eye irritation and corrosion potential.
To learn more about either the Eye Irritation Test or Short Time Exposure assay, please visit http://www.cyprotex.com/topicalandcosmetics/skin-and-ocular-testing#ocular or contact us.