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Editors Selection IGR 11-1

IOP-Related: Water-drinking test, pulse amplitude and choroidal thickness

Comment by Helen Danesh-Meyer on:

22527 Choroidal expansion during the water drinking test, Vasconcelos De Moraes CG; Castro Reis AS; de Sá Cavalcante AF et al., Graefe's Archive for Clinical and Experimental Ophthalmology, 2009; 247: 385-389

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Water-drinking test, pulse amplitude and choroidal thickness Comment by Helen Danesh-Meyer, Auckland, New Zealand Eighty years following the initial observation by Schmidt that intraocular pressure (IOP) increases following ingestion of water, there is a resurgence of interest in the role of the waterdrinking test (WDT) in the investigation of glaucoma. The impetus behind these studies is the view that IOP spikes and diurnal IOP variation are important in the progression of glaucoma and that a single IOP measurement in the clinic does not necessarily reflect what is happening to an individual's IOP through the course of the day. De Moras et al. (225) hypothesize that an increase in choroidal volume occurs following the WDT and that this explains, in part, the elevation which may be associated with this test. To test their hypothesis, they subjected 30 patients (20 after WDT and 10 controls) with open-angle glaucoma to serial IOP measurements using dynamic contour tonometry (DCT), Goldman tonometry (GAT), and choroidal thickness measurements using ultrasonographic A and B-scan. They found that there was an increase in IOP following WDT, consistent with the results of other investigators. They additionally concluded that choroidal thickness increased by 200 µm 95% CI (170 -230 µm). To measure choroidal thickness the investigators used a 10-MHz B probe (200-µ resolution). While this technique provides a measurement, it has not been validated to accurately and consistently estimate choroidal thickness in human eyes. However, the possibility that abnormal regulatory mechanisms in choroidal vasculature may result in alterations in choroidal volume in eyes with glaucoma is intriguing and merits further investigation. Certainly, sympathetic stimulation has been shown to occur with water drinking and plasma noradrenalin levels increase after water drinking by a magnitude at least as great as that elicited by smoking two unfiltered cigarettes or ingesting 250 mg of caffeine. The ability of newer technologies to determine choroidal thickness reliably will contribute to our understanding of mechanism the underlying the WDT.

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