This study compared the intraocular pressure (IOP) peak, mean and fluctuation during the water drinking test to a modified diurnal tension curve (mDTC). Although IOP is the most important risk factor for development and progression of glaucoma, it remains poorly explored. In this study, 50 untreated primary open-angle glaucoma (POAG) patients received a mDTC with measurements every two hours from 7:00AM to 3:00 PM. The WDT was performed thereafter.
The average peak IOP was 27.8 ± 4.0 mmHg during the WDT and 24.9 ± 3.1 mmHg during the mDTC (P < 0.001). The average mean IOP was 25.8 ± 3.6 mmHg (WDT) and 22.3 ± 2.4 mmHg (mDTC). The average IOP fluctuation was 6.6 ± 2.9 mmHg (WDT) and 4.7 ± 2.0 mmHg (mDTC). There was limited agreement between mDTC and WDT IOP values due to the higher IOP values from WDT compared to the mDTC.
IOP peaks triggered by the WDT may reveal instability of IOP inconsistent with controlled glaucoma, in a similar fashion as a cardio stress test may reveal coronary ischemia not seen in physiologic states
Higher IOP values during the WDT compared to IOP measurements during a steady state situation (physiologic situation such as mDTC) is expected from a stress test such as the WDT. Stress tests have been widely employed in medicine to assess changes in physiological systems when stressed. Clinicians can detect signs that allow a more accurate estimation of future events.1 During the WDT, eyes with worse outflow facility tend to experience higher IOP peaks and fluctuation than eyes with normal outflow. Higher mean, peak and greater fluctuation in IOP are known to be associated with incidence and worsening of OAG.2,3 IOP peaks triggered by the WDT may reveal instability of IOP inconsistent with controlled glaucoma, in a similar fashion as a cardio stress test may reveal coronary ischemia not seen in physiologic states. Also, 30% of normotensive glaucoma patients have IOP peaks greater than 21 mmHg during the WDT.4
Besides the author's suggestions, another possible explanation for the moderate agreement between both tests is that only one mDTC was done in this study. Higher IOP values may occur in different days. POAG patients do not manifest a repeatable diurnal IOP pattern from day to day. Measurement of single-day IOP variation can poorly characterize the short-term IOP variation.5 On the other hand, IOP peak and mean during WDT are quite reproducible in different days and months.6,7
Measurement of single-day IOP variation can poorly characterize the short-term IOP variation5 On the other hand, IOP peak and mean during WDT are quite reproducible in different days and months
The authors were accurate in concluding that peak and mean IOP can be estimated from the WDT, which is quicker, compared with the mDTC. Reducing the time during office examinations is also important due to the COVID-19 pandemic outbreak constraints.