Water drinking test: The second innings scorecard

Even though both intraocular pressure (IOP) fluctuation and peak IOP have been demonstrated to be significant risk factors for glaucoma progression, the latter has been shown to be a better predictor of disease progression. Peak IOP is also a more practical tool for guiding management protocols.[1-3] Continuous 24 h IOP monitoring arguably provides the best measure of an individual’s IOP, but is logistically not possible in clinical settings. A diurnal variation of IOP over 24 h provides a better understanding of an individual’s IOP profile including mean and peak IOP, as well as IOP fluctuation.[4,5] All of the currently available methods of recording circadian IOP variations are resource and time intensive, and usually not feasible in routine glaucoma practice. It is for bridging this lacuna that the water drinking test (WDT) has seen a resurgence in in glaucoma assessment and management. The WDT was initially used as a diagnostic test for glaucoma, and its use fell out of favor, understandably, because of its low sensitivity, specificity, and diagnostic value.[6,7] However, given that the WDT measurements correlate well with diurnal tension curves, it may be considered as a more cost effective and efficient surrogate for the more time-consuming IOP phasing. The WDT, therefore, has seen a recent revival as a “stress test” to assess the capacitance of the aqueous outflow, an indirect tool to measure aqueous outflow facility, along with peak IOP and IOP fluctuation.[8]