Effects of Benzalkonium Chloride on Pilocarpine-induced Opacity in Porcine Isolated Corneas

Abstract

The incubation of isolated porcine corneas (intact, with the epithelium or endothelium plus Descemet's membrane removed, or with both the epithelium and endothelium plus Descemet's membrane removed) with solutions of pilocarpine HCl (5 X 10 4M or 5 x 10-3M) for four hours caused very little increase in opacity when compared with corneas incubated with physiological saline. However, at a higher concentration (5 x 10-2M), the application of pilocarpine to the endothelial surface, or to both the epithelial and endothelial surfaces of intact corneas, caused an obvious increase in opacity. The addition of the preservative benzalkonium chloride (BC; 0.005%) to pilocarpine solutions caused an increase in opacity, but in no circumstances did this appear to be other than an additive effect, since incubation with BC alone had an opacifying effect. This in vitro test confirms that pilocarpine is a safe drug for application as eye-drops. Studies using high performance liquid chromatography showed that BC increased the amount of pilocarpine passing through the cornea from the epithelial to the endothelial surface. A small amount of BC also passed through the cornea over the 4-hour experimental period.