Background: solutions. The aim of this study was to compare the cytotoxic effects of BAC-containing ophthalmicsolutions with a BAC-free ophthalmic solution using an organotypic 3-dimensional (3-D) cornealepithelial model and to determine the effects of latanoprost ophthalmic solution and its BACcontainingvehicle on corneal thickness in a monkey model.Benzalkonium chloride (BAC) is a common preservative used in ophthalmicMethods: latanoprost (0.02% BAC) and olopatadine (0.01% BAC) was compared to that of BAC-freetravoprost and saline in a corneal organotypic 3-D model using incubation times of 10 and 25minutes. To compare the extent of differentiation of 3-D corneal cultures to monolayertransformed human corneal epithelial (HCE-T) cell cultures, expression levels (mRNA and protein)of the corneal markers epidermal growth factor receptor, transglutaminase 1 and involucrin werequantified. Finally, latanoprost ophthalmic solution or its vehicle was administered atsuprapharmacologic doses (two 30 corneal pachymetry was performed at baseline and at weeks 4, 13, 26 and 52.The cytotoxicity of commercially available BAC-containing ophthalmic formulations ofµL drops twice daily in 1 eye for 1 year) in monkey eyes, andResults: cytotoxicity between the BAC-containing latanoprost and olopatadine ophthalmic solutions andBAC-free travoprost ophthalmic solution at either the 10- or 25-minute time points. The 3-Dcultures expressed higher levels of corneal epithelial markers than the HCE-T monolayers,indicating a greater degree of differentiation. There were no significant differences between thecorneal thickness of monkey eyes treated with latanoprost ophthalmic solution or its vehicle (bothcontaining 0.02% BAC) and untreated eyes.In the 3-D corneal epithelial culture assays, there were no significant differences inConclusion: suggests that the levels of BAC contained in ophthalmic solutions are not likely to cause significantdirect toxicity to epithelium of otherwise normal corneas.The lack of cytotoxicity demonstrated in 3-D corneal cultures and in monkey studies