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Editors Selection IGR 9-2

Clinical Examination: Water-drinking test

Comment by Robert Ritch & Gustavo de Moraes on:

51157 Choroidal thickness change after water drinking is greater in angle closure than in open angle eyes, Arora KS; Jefferys JL; Maul EA et al., Investigative Ophthalmology and Visual Science, 2012; 53: 6393-6402

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Arora et al. prospectively studied choroidal thickness (CT) changes using enhanced depth imaging optical coherence tomography (EDIOCT) in patients with open-angle (OAG) and angle-closure glaucoma (ACG) after a water drinking provocative test (WDT). They observed a significant increase in CT and a decrease in anterior chamber depth after the test in ACG but not in OAG eyes. They suggested that dynamic choroidal changes may play a role in the pathogenesis of ACG and postulated that eyes with a greater increase in CT would be more likely to develop ACG. This is a clinically relevant finding, and, above all, heightens the existing compelling evidence regarding the usefulness of the WDT in glaucoma management.¹

The relationships between the choroid and the mechanisms underlying angle closure were initially hypothesized by Lowe² and Kirsch³ in the 1960s. Since high-resolution imaging techniques were not available at that time, it is gratifying to see that Arora et al. succeeded in substantiating these hypotheses in the current era of non-invasive, high-quality, imaging technologies. In 2008, when the EDI-OCT technique was not yet developed, De Moraes et al.⁴ performed the WDT at 15-minute intervals in a sample of OAG patients and measured the 'retina-choroid-sclera' complex changes using ocular ultrasonography. They also measured the ocular pulse amplitude (OPA) provided by Dynamic Contour Tonometry (DCT) as a means to investigate the relationship between OPA and CT. Despite the limitations of the technique available in that time, they observed a significant positive correlation between OPA and CT changes, as well as a dynamic, temporal relationship between CT increase and IOP elevation at the measured intervals.

Regrettably, Arora et al. spent much of their discussion criticizing the results of De Moraes et al. without reporting the meaningful differences in methodology and conclusions between the two papers. For instance, Arora et al. performed a single CT measurement after 30 minutes of water load, which prevented them from (1) detecting IOP peaks and CT changes that occurred before or after this timepoint and (2) investigating the longitudinal changes in CT, IOP, and anterior chamber depth which would have been valuable to better understand the temporal relationships among these variables after the WDT when it is performed as recommended.^5-11 Neither did they mention that the EDI-OCT was unavailable prior to their study, preventing comparison. Finally, the conclusions of the two papers are clearly distinct: Arora et al. found no significant correlation between IOP rise and CT increase in OAG, whereas De Moraes et al. observed a significant positive correlation between OPA and CT changes. Therefore, the criticisms by the former authors have no scientific basis.

Both papers highlighted dynamic choroidal changes after the WDT. Clinically, it is important to differentiate the usefulness of this test in eyes with ACG and OAG. Arora et al. have contributed significantly to understanding how choroidal changes relate to anterior chamber depth changes and ACG. While the WDT has been long used to stress the outflow facility of OAG eyes and assess IOP peaks that may occur outside office hours,9,11 future investigations could promote another use of the WDT, that is, to determine which patients with narrow angles are more likely to present changes in anterior chamber anatomy predisposing to angle-closure.

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