gms | German Medical Science

With a cornea penetration model using pig eyes, the morphological effect of preservatives on the corneal parenchyma was examined. The goal of this study was to establish this in vitro method.

Freshly obtained pig corneas were fixed with an O -ring in an Frantz-type-diffusion system. Under physiological conditions (Tears buffer, Aqueous humor buffer, 37°C) the test-solution was applied to the epithelial side (donor chamber) and could now diffuse to the endothelial side (acceptor chamber). Preservatives, such as Benzalkonium chloride (BAC) with a concentration of 0,02 %, Cetrimide 0,02 %, Benzoxonium chloride 0,02 %, and others were tested. They were kept in contact with the cornea for up to 300 minutes. After different contact times (30, 60, 120, 180, 240, 300 minutes) the corneas were sampled and immersed into formalin solution for histological analysis. The pig corneas were rated with a histological score as following: epithelial edema, graduation I - IV, stromal edema, graduation I-II and the condition of the corneal endothelium (intact or damaged).

There was a clear correlation of corneal damage in function of incubation time. The increase in epithelial edema and in stromal edema could be demonstrated for the preservatives in varying degree. BAC showed by far the most pronounced effect on corneal parenchyma. Control eyes incubated with buffer only, did not exhibit these changes. A damaged corneal endothelium was used as a exclusion criterion.

This in vitro model offers the possibility to test and quantify the potentially toxic effects of ophthalmic excipients or complex solutions in a rapid way. Additionally it helps reducing in vivo experiments with rabbits.