The absorption and consequently the bioavailability of topical ophthalmic drugs is limited by the anterior eye segment barriers such as nasolacrimal drainage, reflex blinking, tight corneal barriers and proteins and metabolic enzymes of tear fluid. In order to increase the bioavailability of ophthalmic drugs, reduce the side effects due to unproductive absorption into systemic circulation and reduced dosage frequency, innovative pharmaceutical forms of topical ophthalmic drugs are being investigated and developed. The potential of O/W nanoemulsion in ophthalmic drug delivery is based on the similarities of the nanoemulsion with the tear film. Since most of the ophthalmic drugs are poorly soluble in water, their encapsulation into the O/W nanoemulsion oil phase increases drug solubility. With the aim of prolonging the nanoemulsion retention on the surface of the eye, the droplet surface is modified by addition of cationic surfactants or polymers, which makes the droplets positively charged. The key parameter in the process of developing a final dosage form is its stability. The aim of this thesis is to examine the stability of the cationic O/W nanoemulsion whose oil phase makes the Mygliol 812, surfactants lecithin S45 and Cremophor EL, and pseudo-emulsifier cationic polymer chitosan. Nanoemulsions were prepared by a high-energy microfluidization method. The stability of nanoemulsion was tested after storage for 30 days at room temperature and at 4 ° C, accelerated stability testing methods and after dilution with simulated tear fluid. As stability parameters, the size of the droplet, the polydispersity index and the zeta potential of the nanoemulsion were considered. Determination of the stability of the nanoemulsion in real time at 4 and 25C indicates the need to store the nanoemulsion at lower temperatures. After accelerated aging tests were performed, the droplet size and polydispersity index of cationic nanoemulsion increased, followed by a mild increase in potency, but there was no creaming or phase separation, indicating good kinetic stability of the formulationsMixing the nanoemulsion with the simulated tear fluid at a ratio of 40: 7 did not induced any significant changes to the droplet size, polydispersity index nor zeta potential.