A water-drinking test can induce hemodynamic, pattern electroretinogram (pERG) and other changes in the eye that may serve as a predictor for glaucoma progression, say researchers with the Bascom Palmer Eye Institute in Miami. With only 16 subjects, the study may sound all wet, but both structural and functional testing help float the concept. The 16 subjects—all of whom had healthy vision—were asked drink some bottled water at room temperature within five minutes. Their intraocular pressures (IOPs), time-integrated brachial blood pressures, heart rate and pERG latency were noted before they began the test and every 15 minutes—for an hour—after. The results were more than just a drop in the bucket. In fact, with an IOP increase of 1.7mm Hg ± 1.8mm Hg after half an hour, +2.1ms ± 0.9ms pERG latency and significant changes to blood pressure and heart rate, they made quite a splash. The researchers speculate that the test may create changes to the retinal ganglion cell layer due to a reduction of sodium concentration.

This new research on the water-drinking test emphasizes “its transient neurovascular effects in addition to IOP elevation,” which is what it is currently used for. “It is plausible that the pERG changes could have a been of greater magnitude in glaucomatous eyes, therefore suggesting its utility as a street test for retinal ganglion cell function and, hence, potential application for risk assessment,” the study notes. It also adds some ideas that may leave a new wave of research in its wake. “In principle assessing pERG changes after a water-drinking test might also offer the opportunity to test the protective effects of medications of transiently induced retinal ganglion cell dysfunction.”