APPLICATION OF IN-VIVO CONFOCAL MICROSCOPY TO THE UNDERSTANDING OF SURFACTANT-INDUCED OCULAR IRRITATION

The purpose of this study was to assess the ability of in vivo confoca l microscopy (CM) to provide noninvasively derived histopathologic cor relates of surfactant-induced eye irritation from which specific patho logic mechanisms can be identified and Inter evaluated in alternative in vitro models. Rats and rabbits, divided into groups of 5, received 10 mu l of an anionic or cationic surfactant in one eye with the other eye used as a control. At specified times, eyes were examined and sco red for ocular irritancy using a penlight and slit-lamp. Subsequently, corneas were evaluated by in vivo CM to evaluate epithelial layer thi ckness and surface epithelial cell area, corneal thickness, depth of n ecrosis, inflammation, fibrosis, and endothelial injury. At 3 hr, the anionic surfactant produced slight irritation with peak scores of 12.4 and 8.0 out of a possible 110 in the rats and rabbits, respectively. In vivo CM revealed changes limited to the corneal epithelium that dec reased in thickness to 78% in rats and 81% in rabbits at 3 hr. This de crease in the thickness correlated with a significant decrease in surf ace epithelial cell area from 2,061 +/- 395 mu m(2) to 567 +/- 330 mu m(2) in the rats and 1,523 +/- 185 mu m(2) to 934 +/- 71 mu m(2) in th e rabbits (p < 0.005 and 0.005, respectively). The cationic surfactant produced severe irritation in both the rats and rabbits with peak sco res of 85.4 and 80.2 occurring at day 2, respectively. In vivo CM in t he rats showed complete loss of corneal epithelium, lysis of keratocyt es, and loss of corneal endothelium. In the rabbits, injury appeared l imited to the anterior cornea with complete loss of epithelium and los s of keratocytes extending to 52% of the corneal thickness. These find ings establish the application of noninvasive, in vivo CM to qualitati vely and quantitatively characterize the pathobiology of ocular irrita tion in situ. This information will be important in the development an d evaluation of mechanistically based in vitro alternatives for ocular irritancy testing.