Does peak intraocular pressure measured by water drinking test reflect peak circadian levels? A pilot study

Background: To determine whether there is a correlation between peak intraocular pressure (IOP) measured after water drinking test (WDT) and patient's peak daytime IOP. Methods: Patients who were diagnosed with glaucoma, ocular hypertension and/or glaucoma‐like discs were enrolled in this prospective observational pilot study. All subjects underwent daytime IOP measurement by a single observer using a Goldmann Applanation Tonometer at 3‐h intervals. Subjects were then given 10 mL/kg body weight of water to drink over 5 min; IOP was measured every 15 min for an hour. Correlations between peak IOP and IOP fluctuations as measured by the two methods were analyzed using Pearson's correlation coefficient. Results: Twenty‐five patients were recruited for the study. There were 16 males and 9 females. The mean age was 68.8 ± 8.7 years (50–82 years), and 48% had primary open angle glaucoma. The mean peak IOP measured by diurnal testing (15.52 ± 3.6 mm Hg) was not statistically different from that measured by WDT (15.92 ± 3.2 mm Hg) (P = 0.7). The mean fluctuation in IOP measured during the day (2.32 ± 1.3 mm Hg) was also not significantly different from that measured by WDT (2.24 ± 1.2 mm Hg) (P = 0.8). Though peak IOP measured during diurnal testing showed strong correlation with peak IOP during WDT (r = 0.876), IOP fluctuation measured by the two tests showed poor correlation (r = −0.0789). Conclusion: WDT may provide a satisfactory alternative measure of peak IOP in a clinic setting. A larger sample is required to assess whether it is a good measure of IOP fluctuation.