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Editors Selection IGR 7-2

Clinical examination methods: Water drinking test and progression

Comment by Douglas Johnson on:

13085 The relation between intraocular pressure peak in the water drinking test and visual field progression in glaucoma, Susanna R Jr; Vessani RM; Sakata L et al., British Journal of Ophthalmology, 2005; 89: 1298-1301

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Can we predict who will get worse from glaucoma? Susanna et al. (939) found the water drinking test may help, but is not perfect. In this third paper in their series on the water drinking test,^1-3 a prospective study followed 76 glaucoma patients over two years. Patients were given a water drinking test at the start of the study. The water drinking test involves drinking one liter tap water in five minutes, then measuring the amount of IOP increase over the next 45 minutes. Patients with poor outflow facility are expected to reach higher IOP levels after drinking. Higher IOP after water drinking may also predict greater variability in IOP during a single daily IOP curve, or over the course of time. After the two years, 37% of patients had field progression despite treatment. Those progressing had a higher IOP after the water drinking test (16.8 mmHg from baseline of 12.9 mmHg, vs non-progressors 14.9 mmHg from baseline of 12.6 mmHg). On a proportionate basis, the progressors had an IOP rise of 34%, vs non-progressors rise of only 17%. No other factors were found which separated progressors from stable patients. There are some questions that need to be answered before we can conclude that water drinking is a useful daily clinical test. 1) The IOP during treatment of each group was not reported: did the progressors have a higher IOP? Did the progressors have more variability in IOP over the two years? 2) How did the results of the water drinking test compare with the variability of IOP during a single day of diurnal IOP measurements, or over the two year period? 3) A scatterplot of baseline IOP vs IOP after water drinking for progressors and stable patients is needed to allow the reader to determine the predictability of the test for individual patients. Finally, 4) separating the 25% of patients in each group who had prior glaucoma surgery from those without surgery is needed, as these patients are known to have lower IOP after water drinking and could influence the group outcomes. Described 50 years ago, the water drinking provocative test was initially hoped to predict who would develop glaucoma. Prospective studies revealed too many false predictions to make it a useful test. Susanna and colleagues have been investigating the test to see if it can predict IOP variability, and potentially replace the need for a 24-hour diurnal IOP curve. This is a worthwhile project, and with time this group may succeed.

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