J. Soc. Cosmet. Chem. 27, 301-306 (1976) ¸ 1976 Society of Cosmetic Chemists of Great Britain Eye irritation tests .an of the maximum delay remedial irrigation* assessment time for R. E. DAVIES, S. R. KYNOCH and M.P. LIGGETT? Synopsis--The RABBIT EYE IRRITATION TEST commonly used predictive screening test for assessment of the IRRITANT POTENTIAL of products that may come into contact with the EYE MUCOSA. The rabbit eye is more sensitive to IRRITATION than the human eye, and the less effective protective mechanism is partly responsible for this. Irrigation of the rabbit eye after instillation of a test material might reduce its potential irritancy and more nearly approach the human situation, but due to the sensitivity of the rabbit eye it is unrealistic to apply the same time scale that the human may take to implement remedial IRRIGATION. Results are presented of research carried out to assess the maximum delay time that is acceptable if irrigation of rabbits' eyes with water is to be beneficial in reducing the irritation produced by instillation of sodium lauryl sulphate. INTRODUCTION The rabbit eye has been extensively used for the evaluation of the potential irritancy of cosmetics, toiletries, and household products. The eye of this animal is very sensitive to irritation and corneal damage is readily induced, when com- pared with the human eye. The differences in the protective mechanisms in the rabbit and human eye are at least partly responsible for the exaggerated response * Based on the paper presented to the I.F.S.C.C. London, 28 August, 1974. $ Huntingdon Research Centre, Huntingdon, Cambridgeshire PE18 6ES. 301

302 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in the rabbit eye. In the human, the production of copious amounts of watery tears after an irritant enters the eye, in conjunction with fast blinking helps to dilute and remove the irritant from the eye. The rabbit tear reflex is not as effective as that of the human, and although watery secretions from the tear and Harder's gland, assisted by the action of the eyelids and nictitating membrane, promote the removal of the irritant from the eye, this is neither as rapid nor as efficient as in the human. There is, therefore, some foundation for the suggestion that irrigation of the rabbit eye after instillation of a test material, might well considerably reduce its potential irritancy, and more nearly approach the human situation. The present rabbit eye irritation test most widely adopted is that recommended in the U.S.A. Code of Federal Regulations (1). This test has no provision for irrigation of the eye within 24 h of instillation of the test material. Earlier test methods (2) recommended irrigation of the eye with 20 mls of water 2 and 4 s after instillation of the test material, and in 1972 a test (3) was proposed whereby the eyes of three rabbits were irrigated with 300 mls of water 5 min after instilla- tion of the test material. The difference between 2 s and 5 min clearly indicates a variance of opinion about the length of time that should elapse before irrigation is initiated. Similarly the difference between 20 and 300 mls shows that opinions differ on the amount of water that should be used for this purpose. It was the objective of the research reported here to help clarify those differences of opinion. An attempt was made to find the maximum period of time a particular test material could remain in the eye without causing damage to the cornea, although it is accepted that this time may vary with different materials. Each test was also replicated using quantities of 20 ml and 100 ml of water for irrigation. A well documented anionic sur- factant--sodium lauryl sulphate--was used for these initial investigations. EXPERIMENTAL PROCEDURE New Zealand White strain rabbits in the weight range 2.5-3.5 kg were used in all experiments. The animals were caged separately in metal cages with wire mesh floors and had free access to a pelleted diet (Coney Pellets, 351.B.O.C.M. Silcock) and water at all times. Before experimentation the eyes of all animals were examined and absence of corneal damage confirmed using a 2•o aqueous solution of sodium fluorescein. A 10•o w/v aqueous solution of sodium lauryl sulphate (B.D.H. Limited) was instilled into one eye of each animal by gently pulling the lower lid away from the eyeball to form a cup into which 0.1 ml of the test solution was dropped. The other eye remained untreated and served as a control.