RESEARCH OBJECTIVE: The aim of this study is to compare the findings of optical coherence tomography and functional changes in the visual fields in patients with ocular hypertension and open angle glaucoma. MATERIALS AND METHODS: 68 eyes (38 patients) are enrolled in this study and they are divided into two groups. Group 1 consists of 26 patients (45 eyes) with open angle glaucoma and group 2 consists of 12 patients (23 eyes) with ocular hypertension. All of them underwent complete ophthalmic examination, OCT examination (Cirrus HD-OCT 5000, Zeiss) to measure the thickness of retinal nerve fiber layer (RNFL) and visual field with the Octopus 101 perimeter (Haag-Streit Interzeag), G2 program. This study was conducted in the Eye Clinic University Hospital Split, School of Medicine Split. In statistical analysis were used: Pearson correlation test, T test, Mann-Whitney U test. RESULTS: The study included 38 patients with 68 eyes of which 12 (32%) were men and and 26 (68%) women. The median age of men was 56,6 years (min-max) and women 65 years (min-max). When examining all eyes, MS index has weak positive correlation with average RNFL thickness, RNFL superior and RNFL inferior. A weak positive correlation is observed between MD index and average RNFL thickness, while a negative correlation is observed between MD and RNFL superior/inferior. In eyes with ocular hypertension, significant difference is found between RNFL thickness with indices MD and LV. In eyes with open angle glaucoma, positive correlation is found between RNFL thickness and MS indeks, and negative correlation is observed between RNFL thickness with MD and LV indices. The correlation between RNFL thickness by segment and global indices of visual field is found statistically significant in the superior and inferior segment (P<0,05). CONCLUSION: Extensive structural changes in RNFL thickness measured by OCT indicate functional impairment which are revealed by visual field examination. The average RNFL thickness is not reliable in early diagnosis and monitoring of glaucoma and ocular hypertension, while changes in RNFL thickness by segment (focal changes) are more reliable. The most reliable parameter in monitoring is mean defect (MD) index of the visual field.