284 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS no irritation, comparatively mild inflammatory alterations and gross damage a score of 0, 5 or 10 is awarded respectively. It may be worth emphasizing here that although the minimum scores for iris and cornea are the same (i.e., 5 excluding zero) the maximum iridial score (10) is only twice the minimum corneal score and only one-eighth of the maximum for the latter. The conjunctiva is scored with regard to redness, swelling and discharge, respectively, in a 3:4:3 (i.e., 1:1. 3:1) irritation emphasis ratio and the total score is twice the sum of the individual subscores for these criteria. The minimum conjunctival score (excluding zero) is 2 and the maximum is 20. T.•BLE 5--REsin:rs or EYE IRRrr.¾r•o• TEs'r (A•m•o R.•Bm'rs) Maxi- mum Rabbit Tissue 1 24 48 72 96 7 Possible Number Scored hr. hr. hr. hr. hr. days Score 1 Cornea 30 Iris 10 Conjunctiva 10 Total 50 2 Cornea 30 Iris 10 Conjunctiva 8 Total 48 3 Cornea 30 Iris 10 Conjunctiva 8 Total 48 4 Cornea 30 Iris 10 Conjunctiva 8 Total 48 5 Cornea 30 Iris 10 Conjunctiva 8 Total 48 30 30 30 20 15 80 10 10 10 10 10 10 10 6 8 8 4 20 50 46 48 38 29 110 30 30 30 20 20 80 10 10 10 10 10 10 4 4 8 8 4 20 44 44 48 38 34 110 30 30 20 20 5 80 10 10 10 10 5 10 4 4 4 4 4 20 44 44 34 34 14 110 30 10 10 10 5 80 10 10 10 10 10 10 4 6 8 8 6 20 44 26 28 28 21 110 30 20 20 20 10 80 10 10 10 10 10 10 6 6 6 6 6 20 46 36 36 36 26 110 Mean scores Cornea 30.0 30.0 24.0 :22.0 18.0 11.0 80 Iris 10.0 10.0 10.0 10.0 10.0 10.0 10 Conjunctiva 8.4 5.6 5.2 6.8 6.8 4 8 20 Mean Total Scores 48.4 45.6 39.2 38.8 34.8 25.8 110 Having discussed the scoring system in some detail, an illustrative example is in order. In Table 5 data for an actual eye irritation test are presented. The test material was an experimental shampoo and the results following the instillation of 0.1 ml. quantities into the eyes of five rabbits are shown. In each instance, the instillation was made undiluted into the conjunctival sac of the right eye. The left eye of each animal served as an untreated, comparative scoring control. Scores are assembled for

INTERPRETATION OF EYE IRRITATION TESTS 285 each of the three tissues graded at each of the six time intervals for every one of the five animals and are averaged at the bottom of the table. There would seem to be little doubt that this product is an eye irritant but the problem of assigning some distinct and succinct "irritation rating" which would quickly not only translate the over-all irritating response into a simple, readily apprehended form, but also enable comparison with results on other products, still remains. Over the years we have developed a rating system at our laboratories designed to help solve this problem. After completion of a given test the scores are analyzed and a simple, descriptive rating is assigned. At first glance, the process of analysis itself appears somewhat complex but, in essence, the basic criteria for assignment of a given rating are the extent of irritation, its persistence and the over-all consistency of the data. In our classification system, as in the actual scoring system itself, special emphasis is focused upon corneal injury and correspondingly less upon conjunctival and iridial irritation. However, we also take into account persistence TABLE 6--DESCRIPTIVE EYE IRRITATION RATINGS Class Num- Descriptive ber Rating Symbol 0 Nonirritating N 1 Practically nonirritat- PN •ng 2 Minimally irritating M• 3 Mildly irritating M2 4 Moderately irritating M• 5 Severely irritating S 6 Extremely irritating E 7 Maximally irritating Mx and consistence of response. As a result of classification, a product is assigned one of eight possible de- scriptive eye irritation ratings. These are shown in Table 6. Comparatively few cosmetic prod- ucts (or, for that matter, any other general class of products) have been assigned over the years to the "Non- Irritating" category and the same applies to the "Maximally Irritat- ing" class. Actually, cosmetic for- mulations as a whole, both experimental and commercial, tend to fall into one of the middle four classes. Some of our clients use the "Moderately Irritating" category as a "cut-off point" and reject all experimental formulations showing eye irritation greater than this from further con- sideration. The rating system we use is carried out in a series of three steps. The first two steps are shown in Table 7. Going back to the example in Table 5, the result of carrying out the first two steps in classification is the assignment of a tentative rating of "Moderately Irritating." The highest mean total score is 48.4 and this occurs at the one-hour point. The incidence of this score plus or minus five points is 100 per cent (five out of five rabbits), well over the 40 per cent requirement of Step 1. The value of 48.4 falls within the 25-50 point range for the "Moderately Irritating" class. The next step is shown in Table 8. The purpose of this third step is to