The presence of preservatives in eye drops, may have, depending on the concentration, cytotoxic influence on the corneal and conjunctival cells, and may cause the patients’ subjective inconveniences. The authors compare the benzalconium chloride (BAC) concentrations in individual drug used for glaucoma treating. The daily dose of BAC was calculated according to the drop’s size and BAC concentration. The daily dose of BAC differs depending on the selected therapy markedly – doses in the range from 0 to 10 micrograms were found. The BAC concentration is one of important factors affecting the patient’s compliance in the treatment of the primary open angle glaucoma.

        Key words: primary open angle glaucoma, antiglaucomatics, benzalconium chloride