BACKGROUND/AIM Glaucoma has been noted to be more prevalent and aggressive in blacks. Treatment of glaucoma involves lowering of intraocular pressure (IOP) to a targeted level where further glaucomatous damage is unlikely. High IOP peaks and fluctuations which are among significant risk factors for glaucoma development and progression can be detected through Water Drinking Test (WDT) and phasing. The aim of this study was to determine as well as compare the mean follow-up clinic IOP, mean IOP peaks and fluctuations during WDT and modified phasing in POAG patients on medical treatment at the glaucoma clinic of Enugu State University of Science and Technology Teaching Hospital Parklane (ESUTTHP), Enugu with a view to determining those patients at risk of glaucoma progression. METHODS The study was a hospital based cross sectional study on POAG patients on medical treatment attending the eye clinic of ESUTTHP, Enugu. Patients were selected by simple random sampling. Their eyes were examined which included visual acuity assessment, follow-up clinic intraocular pressure measurement, gonioscopy, anterior and posterior segments examination. WDT and modified phasing were carried out on them. WDT was done over 2 hours after intake of 1 liter of water with intraocular pressure measured every 15 minutes. Modified phasing was done over 8 hours with intraocular pressure measured at 2 hourly intervals. Data analysis was done using SPSS version 20 (U.S.A). The mean follow-up clinic intraocular pressure (IOP), IOP peak and fluctuation during WDT and phasing were determined and compared using T-test. Pearson’s correlation was used to find the correlation between mean IOP peaks and fluctuations in WDT and phasing.