The chorioallantoic membrane in irritation testing.

The chorioallantoic membrane (CAM) of the chick embryo is a fusion membrane with a blood vessel complex. It was examined as a possible means of predicting the irritant potential of chemicals for the conjunctiva, as observed in the Draize eye test. Nine chemicals of known irritancy potential for the eye in vivo were selected from published data, and each was tested at four different concentrations. The treated CAMs were examined macroscopically at 4, 24 and 48 hr after treatment, and were then prepared for histological examination. A dose response was observed for each chemical. In only four of the nine chemicals could the response in the CAM be considered to predict the in vivo activity. In another two, the correlation was poor. Three chemicals, glycerine, polyethylene glycol and Tween 80, all reported to be harmless to the eye, were embryotoxic at more than one concentration. Histological changes were degeneration or necrosis at the treated site without the chemical features of heterophil (chicken neutrophil) infiltration or significant macrophage infiltration. It is concluded that the CAM is not a suitable tissue for predicting in vivo irritant potential of substances for the conjunctiva, and that it provides no more information than could be obtained from cell cultures.