Comparison of Intraocular Pressure Changes During the Water Drinking Test Between Different Fluid Volumes in Patients With Primary Open-angle Glaucoma

Purpose: The main objective of this study was to compare the intraocular pressure (IOP) response during the water drinking test (WDT) performed with 800 mL, 1000 mL, and 10 mL/kg of body weight and to test its relationship with body mass index (BMI). Methods: In this prospective, observer-masked, observational study, patients treated with primary open-angle glaucoma were evaluated. In group I, 29 consecutive patients with body weight ≤60 kg underwent an 800 mL fluid challenge followed by a second WDT session with 10 mL/kg of body weight no longer than 4 months apart. Group II included 30 consecutive patients with body weight >60 kg who underwent a 1000 mL fluid challenge followed by an 800 mL test no longer than 4 months apart. IOP was measured before (baseline) and after water ingestion every 15 minutes for 45 minutes. Results: In group I, there was no significant difference in baseline or peak IOP between 800 mL and 10 mL/kg of body weight tests (P=0.12 and 0.56, respectively). However, 10 mL/kg tended to lead to consistently lower IOP values and a biased response in eyes with higher IOP. In group II, there was also no significant difference in baseline or peak IOP between 800 and 1000 mL tests (P=0.26 and 0.72, respectively). No biased response was observed in this group. There was no significant association between IOP peak and BMI with 800 mL (P=0.18), 10 mL/kg (P=0.29), or 1000 mL (P=0.34). Conclusions: There was overall good agreement between WDT results with different fluid volumes. The response to the volume loads tested in this study was not influenced by the BMI.