Early prediction of the eye-related bioavailability is critical to efficient development of topical ophthalmic drugs. The aim of the research project of which this diploma thesis is an integral part is to standardize in vitro/ex vivo models of optimum capacity to predict eye-related bioavailability. The routine use of these models would significantly contribute to the successful development of ophthalmic drugs.In vitro corneal epithelial model was in the focus of this diploma thesis. Special importance is given to the permeability assays with hydrophilic and macromolecular markers of paracellular pathway, which together with transepithelial electric resistance are indicators of barrier integrity. This characterization is important in order to confirm the model applicability in terms of studying paracellular transport, which represents the aim of this diploma thesis. We have determined the permeability of fluorescently labeled dextran (FD-4), a hydrofilic macromolecular marker of paracellular transport. Moreover, by using ethylenediaminetetraacetic acid disodium salt (EDTA), as an enhancer of paracellular absorption, we tested the possibility of permeability enhancement by opening the tight junctions. By measuring the transepithelial electrical resistance, the effect of EDTA on the tight junction opening between the epithelial cells was also confirmed. Furthermore, the apparent permeability coefficient of the paracellular marker increased by increasing the concentration of EDTA. The cytotoxic effect of EDTA was excluded by examining the viability of model after testing permeability. These results indicate the potential of in vitro corneal epithelial model for studying paracellular transport of ophthalmic drugs.