Optimizing the water drinking test: evaluating the reproducibility and validity of a shortened protocol: a randomized prospective trial

Purpose: This study aimed to evaluate a a shortened Water drinking test (WDT) protocol and explore potential factors of patient characteristics such as body mass index (BMI) or Body Surface Area (BSA). Methods: This was a prospective, randomized study comparing two validated WDT dosage regimens: 10 mL/kg and a fixed 800 mL intake. Patients were randomly assigned to one of the two groups. The initial 30 min IOP response was compared to the full 60 min test to assess correlation and predictive value. Additionally, the effect of BMI or BSA on IOP dynamics was investigated. Results: Of the 100 enrolled patients, 90 were randomized and the final analysis included 45 patients in the 800 mL group and 35 in the 10 mL/kg group. No significant differences were found between groups in demographic, systemic, or ocular characteristics. The WDT showed strong reproducibility, with high correlations between the 30 min and 60 min tests (r = 0.89, p < 0.001). On the contrary, BMI (r = 0.12, p = 0.26) and BSA (r = 0.16,p = 0.14) had weak correlations with IOP response. Conclusion: The 30 min WDT is a reproducible and reliable method for assessing IOP fluctuations, offering a practical alternative to the full 60 min protocol. BMI and BSA had weak correlations with IOP response, suggesting that adjusting WDT outcomes based on BMI or BSA may be unnecessary.