Written by Sam Thistleton
The majority of the personal care and beauty products we buy are not designed to come into direct contact with our eye surface, or cornea, nevertheless accidental exposure can happen like shampoo running into our eyes in the shower, inadvertently rubbing our eyes with product on our hands or just the proximity of colour cosmetics that are applied very close to our eyes. It’s necessary therefore for all cosmetic product to have been tested for eye irritation.
The term eye irritation refers to feelings of dryness, itchiness, pain, or grittiness in the eye. Many factors can cause eye irritation, including injuries, dry eye, and infection, however, efficient product testing can ensure that exposure to the everyday products we use should not contribute to this.
- Itchy, watery or teary eyes
- eye redness
- eye pain
- blurred vision
- light sensitivity
Eye irritation is defined as the production of changes in the eye following the application of a test substance to the anterior surface of the eye, which are fully reversible within 21 days of application.
Compare this to the more serious end point of eye corrosion, which is the production of tissue damage in the eye, or serious physical decay of vision, following application of a test substance to the anterior surface of the eye, which is not fully reversible within 21 days of application.
Eye Irritation testing
Historically the Draize test is synonymous with eye irritation testing. Draize eye irritation tests observe changes of cornea, conjunctiva, and iris in rabbit eyeballs following the exposure to test substances. This inhumane in vivo test sees a chemical applied on the cornea and conjunctival sac of one eyeball of a conscious rabbit while the other eyeball remains untreated for the negative and paired control and the rabbit is then euthanised following the test.
The development of in vitro methods has meant that the Draize test is now redundant, however it is still used across the world.
In vitro methods
The following two tests would class as ‘not tested on animals’ or ‘non-animal testing’ – but see what you think when you’ve read the methods!
The HET-CAM test (hen’s egg-chorioallantoic membrane test) is a test used to determine the irritation potential of substances and is an alternative test to the Draize Rabbit Eye Test. In the test, incubated hen’s eggs are opened carefully on day 9 and the chorioallantoic membrane (CAM) is exposed.
Test substances, a pure or diluted solution, are placed directly on the exposed CAM membrane, and the membrane is inspected visually through a microscope.
The Bovine Cornea Opacity/Permeability test (BCOP) is an alternative ocular irritation assay designed to replace the rabbit eye test. It is commonly utilized to test for eye irritation and corrosive potential of test materials that may be used in or around the eye. The BCOP uses excised bovine corneas, normally discarded as waste in the production of beef and does not utilise live animals for research.
If you are truly against animal testing, wanting to claim this on pack and to consumers, or are working with a vegan brand or products then can you hand-on-heart be happy using wither HET-CAM or BCOP for your eye irritation studies?
The trouble with animal models
I found a very interesting article written by Stephen R. Kaufman, M.D, an ophthalmologist
“The following are some of the fundamental anatomical differences between the rabbit and human eyelid, tearing mechanism, and cornea:
- The rabbit epithelial (surface) layer is 10 times more permeable to hydrophilic solutes than the human eye.
- Bowman’s membrane (the next layer) is six times thicker in man.
- The rabbit’s threshold of pain in the eye is much higher than that of humans, so irritating substances are not washed away as readily.
- Rabbits have a less efficient tearing system than humans.
- Unlike people, rabbits have a nictitating (winking) membrane (third eyelid), which has an unclear effect on elimination of foreign materials.
- Humans develop corneal epithelial vacuoles in response to some toxic substances, but rabbits do not.
- The rabbit mean corneal thickness is .37 mm, while that of man is .51 mm.
- Rabbits are more susceptible to damage (alkaline) materials, because the pH of their aqueous humor is .82 compared to .71-.73 for man.
- The cornea represents 25% of the rabbit eye surface area, but only 7% of the surface area in man.”
He noted that “due to these differences, Draize data correlates poorly with actual human experience.”
Cue 100% animal-product-free testing
To help guide us in achieving our mission we have created an ethical scale that we use to inform our decision-making. Categorising the use of animal components like this helps us remember that the vast majority of in vitro tests using cell culture are only at Level 2 on our scale, since they use FBS in the culture media. Even though Levels 2-7 are all described as in vitro, there are big differences between them, so not all in vitro methods are equal when it comes to their animal-product-free status. Using our scale the Draize test would score 1, HET-CAM 3/4 and BCOP 4.
Eye Irritation Test OECD TG 492 – APF score 5
The Eye Irritation Test (EIT) is an OECD-approved (OECD TG 492) in vitro non-animal test method for identifying chemicals and mixtures that may be irritating to the corneal epithelium. The test method utilises an in vitro reconstructed human corneal epithelium (RhCE) model (EpiOcular™, MatTek Corp. or HCE, SkinEthic™), in an acute exposure assay to support international regulatory labelling requirements, according to the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS). A wide variety of raw materials and formulations come into contact with the eyes, so this regulatory in vitro eye irritation test is ideal if you’re looking for simple Irritant or Non-Irritant classification. Many manufacturers use OECD TG 492 for the purposes of hazard identification and labelling for compliance with a range of legislation including EU REACH and the CLP Regulation. It is approved for chemicals not requiring classification and labelling for eye irritation or serious eye damage, but is NOT intended to differentiate between UN GHS Category 1 (serious eye damage) and UN GHS Category 2 (eye irritation)
Ocular Irritection OECD TG 496 – APF score 7
Ocular Irritection® is a fully defined, biochemical in vitro test that investigates the potential of a substance to cause serious damage, or no irritation to the eye. Eye irritation is a reversible condition caused by changes to the surface of the eye, whereas serious eye damage is not expected to be reversible within 21 days. This method models changes to corneal opacity by observing the effect of a test chemical on a macromolecular reagent matrix. The test can determine whether a substance causes serious eye damage or has no required classification for irritation or eye damage and is an effective first step for a top-down or bottom-up approach to testing as defined in the OECD’s Guidance Document 263: Integrated Approaches to Testing and Assessment (IATA) for Serious Eye Damage and Eye Irritation.
Eye Irritation Test ET50 – APF score 5
If you need to simply establish rank order of mildness or are looking for candidates then this non-regulatory eye irritation test assesses the potency of an ingredient or formulation. The ET50 method provides a profile of damage to the cornea over time resulting in a classification of Severe, Moderate, Mild or Minimal / Non-Irritant. This can be used to rank test items in order of irritation potential or compare them against industry benchmarks.
If you are looking to update your eye irritation testing regime talk to us about the tests available today.