TESTING
TABLE 1: COMPARISON OF EXISTING TESTING METHODS FOR EVALUATION OF OCULAR IRRITATION POTENTIAL2-14 Testing Method
Test Model Draize Eye Irritation Test
Bovine Corneal Opacity and Permeability Test (BCOP)-OECD TG 437
Hen's Egg Test- Chorioallantoic Membrane Test (HET-CAM)
Rabbit Key parameters
■ Redness (Erythema) ■ Swelling (Edema) ■ Discharge ■ Corneal Opacity ■ Ulceration ■ Hemorrhage
Ex vivo bovine cornea
Chorioallantoic membrane of a fertilized chicken egg, typically around 10-12 days of incubation
■ Opacity ■ Permeability
■ Hemorrhage ■ Vascular Effects
Swelling and Redness ■ Tissue Integrity
■ Redness and swelling of the conjunctiva
Eye Instillation Test
Humans (in vivo testing on human eyes)
OECD TG 492 "No Tears" Test
Reconstructed human cornea-like epithelium models
Reconstructed human cornea-like epithelium models
In vivo method: the eye instillation test on humans The Eye Instillation Test on humans is a method that provides direct insights into how products affect human eyes. Its procedure is quite similar to that of the Draize test except that humans rather than animals are used as test subjects. Thus, this test involves applying a product directly to the eyes of human volunteers and observing any resulting irritation or damage. Because it directly measures human eye reactions, it allows a real-world assessment of a product’s impact on human eye tissues. However, there are notable ethical and
practical concerns associated with this test. Ethically, it is invasive and can cause discomfort, pain, or even harm to the volunteers, making it essential to adhere to strict ethical guidelines, informed consent procedures, and participant oversight. Additionally, there is a risk of exacerbating irritation for individuals with pre-existing eye conditions or heightened sensitivity. The variability between test subjects can also influence the results, as individuals may react differently due to genetic factors, age, or health conditions. In addition, it is known from the Draize test on rabbits that the probability of a test product being classified identically on retesting is <50% if the product is in the mild to moderate irritation range.7 As a result, the Eye Instillation Test is
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■ Lacrimation ■ Corneal damage ■ Pupil reaction ■ Eye pain
Cell vitality (one time measurement)
Cell vitality (several time points)
becoming less common and gets gradually replaced by more standardized and less invasive in vitro methods. These alternatives offer a more consistent and ethically responsible way of evaluating product safety while still providing relevant data on potential human eye irritation.
In vitro methods In addition to the Draize Eye Irritation Test, the Eye Installation Test on humans is not ethically justifiable from Dermatest’s point of view, as damage to the eye cannot be ruled out. Nevertheless, testing is very important for
product safety in order to be able to make a statement about the irritative potential. Thus, various in vitro methods have been developed over time to test product safety.
The BCOP and HET-CAM tests Examples of tests that use models of animal origin but not living animals include the BCOP test and HET-CAM test. Both tests are known alternatives for identifying potentially harmful products. The BCOP test, which is also an official OECD guideline (OECD TG 437) involves applying a product to bovine (cow) corneas and assessing the resulting opacity and permeability, which serves as an indicator of eye irritation.8,9
The HET-CAM test uses the
chorioallantoic membrane of fertilized hen eggs to evaluate irritation potential.10,11 Thus, both tests basically help to reduce
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The reactions are visually scored on a scale based on the severity and type of response
Cat. 1 or No Cat. according to UN GHS
The reactions are visually scored on a scale based on the severity and type of response
Evaluation through rating of an ophthalmologist and self assess- ment
Cat 1/2 or No Cat. according to UN GHS
Tailored protocol and prediction model based on ET-50 value determination to identify mild and very mild products
animal testing or pain. Nevertheless, both tests are primarily used for identifying ocular corrosive and severe irritants to, for example,. avoid unnecessary harm to animals in subsequent animal experiments. Furthermore, as stated before, both tests still rely on animal-derived models, which raises concerns about their relevance and accuracy when extrapolating results to human eyes. As a result, these tests may not be suitable
to identify products that are safe for sensitive human eyes, particularly those that are mild or extra-mild. This highlights the need for more refined, human-relevant testing methods.
OECD TG 492 test The OECD TG 492 test is a more recent and ethically advanced development in ocular safety testing. It utilizes reconstructed human cornea-like epithelium (RhCE) models to assess the potential of chemicals to cause eye irritation or serious eye damage. This method marks a significant improvement over traditional animal-based testing, as it uses human-derived tissue rather than the corneas or other parts of animals.
The use of RhCE models makes the test
more relevant to human safety compared to the BCOP or HET-CAM test, as RhCE models mimic the structure, behaviour, and function of human corneal tissue more accurately than animal derived models. This not only addresses ethical
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