The rabbit eye irritation test is a well-established in vivo safety assessment used to evaluate the ocular irritation and corrosion potential of chemicals, cosmetics, medical device extracts, and consumer products. Guided by internationally recognized protocols such as OECD Test Guideline 405 and ISO 10993-10, this test provides critical data for hazard classification, labeling, and regulatory submissions worldwide. This article explains the technical principles, sample types, scoring criteria, testing procedures, and frequently asked questions related to the rabbit eye irritation test.
Technical Overview
The rabbit eye irritation test, historically known as the Draize eye test, is an acute in vivo toxicity procedure designed to determine whether a substance causes irreversible damage (corrosion or severe irritation) or reversible irritation to the ocular tissue of the eye. Since its introduction in 1944, it has served as the foundational method for ocular hazard assessment across chemical, cosmetic, pharmaceutical, and medical device industries.
Modern testing follows a structured, humane strategy. Under OECD Test Guideline 405, the in vivo test is performed only when existing data, quantitative structure-activity relationships, pH screening, and validated in vitro methods are insufficient to classify the substance. The "3Rs" principle—Replacement, Reduction, and Refinement—is strictly applied, limiting animal use to the minimum number necessary to obtain a conclusive result.
- Primary standard: OECD TG 405 (Acute Eye Irritation/Corrosion)
- Medical device standard: ISO 10993-10 and GB/T 16886.10 (Tests for irritation and skin sensitization)
- Regulatory frameworks: UN GHS, EU CLP Regulation, REACH, and national chemical regulations
Testing Samples
Industrial and Household Chemicals
Detergents, cleaning agents, solvents, paints, adhesives, and other chemical products intended for professional or consumer use are commonly evaluated for eye hazards. Results directly support classification and labeling requirements under GHS and the preparation of safety data sheets.
Cosmetics and Personal Care Products
Eye-area cosmetics, shampoos, facial cleansers, and similar formulations may require ocular safety data depending on regional regulatory requirements. Where animal testing is restricted, validated in vitro alternatives are typically used to support the safety assessment.
Medical Devices and Biomaterials
For devices with eye, skin, or mucosal contact—such as contact lenses, ophthalmic instruments, catheters, wound dressings, and intraocular implants—polar and non-polar extracts are prepared according to ISO 10993-12 and evaluated per ISO 10993-10 for ocular irritation potential.
Pharmaceutical and Agrochemical Formulations
Agrochemical formulations, disinfectants, and pharmaceutical excipients or intermediates may be assessed for eye irritation to support occupational exposure evaluation and product registration dossiers.
Testing Items
The test evaluates specific ocular tissues, each scored using standardized Draize scales at defined observation intervals:
- Cornea: opacity (graded 0–4) and the area of involvement, assessed with or without fluorescein sodium staining to reveal epithelial damage
- Iris: inflammatory lesions, congestion, swelling, and reaction to light (graded 0–2)
- Conjunctiva: redness of the conjunctival vessels (graded 0–3) and chemosis, i.e., swelling of the conjunctiva (graded 0–3)
- Additional observations: ocular discharge, pannus formation, and any other visible abnormalities
- Reversibility: whether lesions resolve within the 21-day observation period, distinguishing reversible irritation from irreversible damage
- Calculated endpoints: maximum average score (MAS) per animal, per time point, and across animals for classification purposes
Testing Methods
Pre-Test Considerations and Sequential Strategy
Before any animal is dosed, a weight-of-evidence review is performed. Substances with extreme pH (≤ 2 or ≥ 11.5), demonstrated dermal corrosivity, or clear evidence of severe eye damage from validated in vitro tests (e.g., OECD TG 437 BCOP, OECD TG 438 ICE, OECD TG 492 RhCE) are presumed corrosive and are not tested in vivo. Testing then proceeds sequentially, typically starting with a single animal before dosing additional animals, and is stopped as soon as a corrosive or severe irritant response is observed.
Standard In Vivo Procedure (OECD TG 405)
- Healthy adult rabbits (commonly New Zealand White) are acclimatized and examined before the test; animals with pre-existing eye defects are excluded.
- A single dose of 0.1 mL of liquid or 100 mg of solid test substance is applied into the conjunctival sac of one eye; the contralateral untreated eye serves as the control.
- The eyelids are gently held together for approximately one second to prevent substance loss, and the eye is not washed for at least 24 hours unless the substance could cause serious injury.
- Ocular reactions are scored at 1, 24, 48, and 72 hours after exposure. If irritation persists, observations continue at intervals until the lesions resolve or up to 21 days.
- Local anesthetics and systemic analgesics may be administered to minimize animal discomfort, in line with refinement requirements.
Medical Device Extract Method (ISO 10993-10 / GB/T 16886.10)
For medical devices, test extracts are prepared using a standard ratio of 0.2 g/mL for thickness ≤0.5 mm samples or 4 cm²/mL (or 6 cm²/mL for irregular surfaces), with polar (e.g., saline) and non-polar (e.g., vegetable oil) vehicles. Extraction is performed at 37 °C for 24 hours or under accelerated conditions. A volume of 0.1 mL of extract is instilled into the conjunctival sac of one eye of each rabbit, with the contralateral eye receiving the corresponding blank vehicle control. Ocular reactions are scored at 1, 24, 48, and 72 hours, and the results are used to determine the ocular irritation response of the device material.
Scoring and Classification Criteria
- GHS Category 1 (serious eye damage): e.g., corneal opacity ≥ 3 in at least 2 of 3 animals, or iritis > 1.5 averaging across animals, with effects that are not fully reversible within 21 days.
- GHS Category 2 (eye irritation): positive responses such as corneal opacity ≥ 1, iritis ≥ 1, or conjunctival redness ≥ 2 in at least 2 of 3 animals that fully reverse within 21 days; Category 2A (irritant) and 2B (mild irritant) are distinguished by recovery time.
- No category: responses below classification thresholds or absent after exposure.
In Vitro Alternatives and Integrated Approaches
Validated alternatives are increasingly used within defined approaches under Integrated Approaches to Testing and Assessment (IATA). The Bovine Corneal Opacity and Permeability (BCOP) test (OECD TG 437), the Isolated Chicken Eye (ICE) test (OECD TG 438), the Short Time Exposure test (OECD TG 491), and Reconstructed human Cornea-like Epithelium (RhCE) models (OECD TG 492) can identify serious eye damage or no irritation, with the in vivo rabbit test reserved for substances that cannot be classified otherwise.
Applications
- Chemical hazard classification and labeling: assigning GHS/CLP pictograms and hazard statements for eye damage or irritation on product labels and safety data sheets.
- Regulatory registration: supporting dossiers under REACH, national chemical inventories, pesticide registration, and biocide programs.
- Medical device biocompatibility: fulfilling ISO 10993-1 evaluation requirements for regulatory submissions, including market approvals in major jurisdictions.
- Product safety and quality control: verifying the ocular safety of formulations during research, development, and post-market surveillance.
- Occupational and transport safety: informing handling procedures, personal protective equipment requirements, and dangerous goods classification.
- Literature and data bridging: providing read-across data for structurally related substances in category approaches.
FAQ
Is the rabbit eye irritation test still accepted by regulators?
Yes. While validated in vitro methods are preferred and used first under OECD guidance, the in vivo rabbit eye test remains an accepted method when alternative approaches cannot deliver a conclusive classification. It is conducted under strict animal welfare oversight, sequential dosing, and early termination rules.
How many animals are used in a typical test?
OECD TG 405 recommends testing one animal first, followed by one or two additional animals only if necessary. A maximum of three animals is typical for a definitive study, significantly fewer than historical protocols.
What is the difference between eye irritation and eye corrosion?
Eye irritation produces reversible damage to the ocular surface that fully resolves within 21 days after exposure, whereas corrosion (serious eye damage) produces irreversible tissue injury, such as persistent corneal opacity or tissue destruction, that does not heal within the observation period.
How is the medical device version of the test different?
The medical device method per ISO 10993-10 evaluates extracts rather than the raw substance. The extract is instilled into the eye in a single application, and reactions are compared against a vehicle control eye to calculate the ocular irritation potential of the device material.
How long does the test take?
A standard study typically takes two to three weeks, including acclimatization, exposure, the 72-hour core observation period, and extended observation up to 21 days if lesions persist. Report issuance may add several additional working days.
Which organizations should perform this test?
The test should be performed by accredited third-party laboratories or in-house facilities holding Good Laboratory Practice (GLP) compliance, with experienced veterinary supervision and animal ethics approvals, to ensure data quality and regulatory acceptance.