RESUMEN
The present study was designed to investigate the long and short term topical effects of Benzalkonium chloride [BAC] on the corneal epithelium with low and high concentrations used in commercial ophthalmic preparations. Forty eight guinea pigs [ninety six eyes] of Dunkin Hartley strains were procured from NIH Islamabad, and randomly divided into four long term [A] and four short term treatment [B] groups. The analysis of the results showed significant decrease [p<0.05] in the thickness and number of epithelial cell layers. The incidence of epithelial desquamation, erosions, and ulceration was more in those experimental groups which received higher concentration of BAC more frequently than those receiving lower concentration and instilled less frequently. It is, therefore, suggested that a better and safe substitute for BAC or preservative free eye drops should be formulated to prevent the hazards of this toxic substance