EYE IRRITATION TESTS 305 In addition to corneal damage, considerable conjunctival redness and swelling were produced, even when the eye was irrigated after 4 s. However, the conjunctiva returned to normal much more quickly in rabbits that were exposed to sodium lauryl sulphate for the shorter period of time. Effects of volume of irrigant No further reduction in the irritant response was observed when volumes of 100 ml of water were used in preference to 20 ml volumes for irrigation of the eyes. However, inexperienced operators may find some difficulty in adequately rinsing certain test materials from the eye when using only 20 ml, and perhaps the larger amount may be advisable for routine experimentation. DISCUSSION Great care is required in the design of laboratory test methods, and in particu- lar it is essential not to lose sight of the objective of the test. Thus, if we decide to irrigate the eye after instillation of a test material we must be sure of our reasons for so doing. For example, we may wish to know if irrigation with water will be beneficial in alleviating the irritation produced by a product accidentally entering the eye of a human being, and how soon after the accident must the treatment begin? If in order to achieve these objectives the rabbit eye is chosen as the 'laboratory model', it must first be accepted that the rabbit eye is different from the human eye. Once this point is accepted it is obviously unreasonable then to apply human standards. Thus to argue that a human being might take 5 min before applying remedial irrigation following the accidental instillation of a product into the eye, and to transpose this time requirement onto the laboratory model, is illogical. In this paper we have only examined the effects of a single test compound, the anionic surfactant, sodium lauryl sulphate. This material was chosen because of its wide use in eye irritation research and because previously it was a common base material in shampoo formulations. The 10•o dilution represented a typical level of surfactant that might enter the eye in a shampoo formulation. Cationic sur- factants were not considered, because of their severe effects on the eye mucosa. However, other types of surfactant, especially where there may be differences in the substantive effects on the eye, clearly need to be investigated. Although individual animals show a wide variation in their response to the same treatment the results obtained in this series of experiments indicate that irrigation must be initiated within 10 s for optimal benefit. The National Academy of Sciences (4) recommended irrigation of some treated eyes 20-30 s after instil- lation as 'there would seem to be some merit in knowing whether prompt washing would prevent injury in the case of accidental contamination with a household

306 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS substance'. This view was supported by the work of Davies and Harper (5) who also recommended the inclusion of a group of animals in the rabbit eye irritation test to investigate the effects of irrigation. We would endorse these views and recommend that any eye irritation test should be extended to include an additional group of animals to investigate the effects of prompt removal of the test material from the eye. Whilst emphasizing that delay should be as short as practicable, it should also be flexible, and tailored to suit the test compound under investigation. The results obtained in these investigations, although variable, showed that when a 10•o solution of sodium lauryl sulphate was instilled into the eye, irrigation must be initiated within 10 s to effect any reduction in the incidence of corneal damage. CONCLUSION In this paper we have attempted to show that the rabbit eye is very sensitive to the introduction of a potential irritant, and any remedial action to remove the irritant from the eye must be prompt. Corneal damage can be produced within 10 s after instillation of a 10•o aqueous solution of sodium lauryl sulphate, and any remedial irrigation must be initiated within this time. (Received: 21 July 1975) REFERENCES (1) Code of Federal Regulations, Test for eye irritants. Title 16, Section 1500.42 (1973). (2) Appraisal of the safety of chemicals in foods, drugs and cosmetics. The Association of Food and Drug Officials of the United States. p. 49. Eye mucosa (1959). (3) Federal Register 37 83 8534, 28 April (1972). (4) Principles and procedures for evaluating the toxicity of household substances. Eye irritants. Natn. Acad. $cL--Natn. Res. Council Publ. 1138 11 (1964). (5) Davies, R. E. and Harper, K. H. The potential irritancy to the rabbit eye mucosa of commercially available cream shampoos. J. Soc. Cosmet. Chern. 18 671 (1967)