Aim of the study: The aim of this study is to examine the impact of cataract surgery, using the method of ultrasound phacoemulsification, onto intraocular pressure in healthy people and in people with open-angle glaucoma. Study draft: Historical cohort study Test subjects and methods: The study includes 30 patients suffering from POAG, who underwent ultrasound phacoemulsification surgery, and 30 patients who underwent ultrasound phacoemulsification surgery who apart from cataracts did not have other associated ocular pathologies. We have measured patient's intraocular pressure by method of Goldman's aplanatine tonometry on the day of surgery, the first postoperative day, the seventh postoperative day, one month after surgery and six months after surgery. We have also recorded data on sex and age. Results: The study included 36.67 % males and 63.33 % females. The arithmetic mean of the test subjects’ age has been 75.3 (7.77) years. Phacoemulsification has had impact on decreasing IOP in patients suffering from POAG. On the day of the surgery the test group manifested IOP of 17 (3.19) mmHg, while six months after the surgery IOP measured 15.5 (2.1) mmHg. On average the pressure decreased for 1.5 mmHg. Difference in IOP before and after phacoemulsification in healthy test subjects was not statistically significant. Conclusion: The research showed that ultrasound phacoemulsification surgery reduces IOP in patients who suffer from POAG. Sex and age didn't have an impact on the change in IOP after surgery in healthy people neither in people with POAG.