Application of in vivo confocal microscopy to the objective evaluation of ocular irritation induced by surfactants

An ocular irritation test using confocal laser scanning ophthalmoscopy has been developed in which corneal lesions subsequent to instillation of surfa ctants are specifically marked by fluorescein and assessed by digital image processing. The sum of the observed fluorescent corneal areas is taken int o account as an endpoint of ocular irritation. Eight currently used nonioni c, cationic and anionic surfactants were applied onto the cornea of rabbits and mice, four rimes per day during 3 days at various concentrations. Benz alkonium chloride, a cationic surfactant, at a concentration range of 0.01- 0.5%, was tested in the same manner. The cornea was evaluated in vivo for o cular tolerance by confocal microscopy. In both rabbits and mice, the test revealed following irritation rankings: cationic,anionic, nonionic surfacta nts. Furthermore, in both animal models, the ocular damage increased with t he concentration of benzalkonium. The test was sensitive enough to detect o cular microlesions at concentrations of surfactants as low as 0.01% for ben zalkonium. These findings demonstrate the usefulness of confocal microscopy for the non-invasive. in situ evaluation of ocular tolerance. (C) 2000 Els evier Science B.V. All rights reserved.