Reproducibility of water drinking test performed at different times of the day

Purpose: To evaluate the reproducibility of water drinking test (WDT) performed at different times of the day, in primary open angle glaucoma (POAG) patients and normal individuals. Methods: Fifteen patients with POAG and 30 normal individuals underwent three WDTs at different times of the day (7 AM, 12 PM, and 5 PM) on 3 different days. Test results in POAG patients and normal individuals were compared. Agreement and correlation of intraocular pressure (IOP) baseline levels, peak levels, and IOP change (peak IOP - baseline IOP) on tests performed at different times were evaluated. Only right eye measurements were analyzed. Results: Mean baseline IOP, peak IOP and IOP change were significantly higher in POAG patients than in normal individuals, at all time intervals (p<0.05). The Bland-Altman analysis demonstrated limits of agreement for IOP peak levels and IOP changes larger than the clinically acceptable (>3 mmHg), even though Pearson's test revealed good correlation among the results. Conclusion: The mean IOP peak and mean IOP change observed during WDT are significantly higher in POAG patients than in control individuals. Low levels of agreement among WDTs performed at different times of the day suggest a poor reproducibility of WDT, which may limit its applicability for the diagnosis and follow-up of glaucoma.