For glaucoma clinicians, a reassuring office intraocular pressure (IOP) can sometimes mask a more troubling reality: some eyes continue to deteriorate despite appearing well controlled. A prospective study from Bascom Palmer Eye Institute suggests that an IOP stress test may help reveal which of these patients are most at risk.
The researchers investigated whether the water-drinking test (WDT) – a standardized physiological challenge that transiently raises IOP – could predict functional and structural glaucoma progression beyond routine office tonometry. The study included 67 eyes from 36 participants with glaucoma, followed for an average of 2.2 years with a mean of 14 testing visits per eye.
For the stress test, participants drank one liter of water within five minutes. IOP was measured before ingestion and again at 15, 30, and 45 minutes. The investigators recorded peak IOP, the rise from baseline, and within-session fluctuation. Visual field mean deviation (MD) and retinal nerve fiber layer (RNFL) thickness were tracked longitudinally using clustered perimetry and spectral-domain OCT.
The average office IOP was 14.8 mmHg, compared with a mean WDT peak of 20.6 mmHg. Crucially, higher stress-test peaks were associated with faster deterioration. Eyes reaching a WDT peak above 21 mmHg experienced significantly faster MD loss than those remaining at or below that threshold and faster RNFL thinning.
The most clinically striking finding came from eyes that appeared well controlled. Based on severity-specific targets, 59 of 67 eyes had acceptable office IOP. And yet 22 of those 59 – 37 percent – exceeded 21 mmHg during the WDT. These eyes subsequently showed considerably faster visual field loss and RNFL thinning than apparently controlled eyes whose stress-test pressure stayed below the threshold.
The discrepancy was even more pronounced among fast progressors. Thirteen eyes met the study’s criteria for rapid functional or structural progression. Routine office measurements would have classified only 3 of these 13 as above target (23%); by contrast, 10 of the 13 reached a WDT peak above 21 mmHg.
Rather than suggesting that drinking water itself creates harmful pressure exposure, the study authors propose that “WDT may be best understood as a composite stress test of the eye’s ability to maintain IOP homeostasis when challenged.” A pronounced response may reveal reduced outflow reserve or a tendency toward pressure peaks that a resting clinic measurement misses. In this sense, the WDT could function much like other physiological stress tests: exposing vulnerability that remains hidden under baseline conditions.
The study remains exploratory. Its cohort was modest, follow-up averaged just over two years, treatment changes were not controlled, and the findings require confirmation in larger multicenter populations.
Nevertheless, it indicates that apparently controlled office IOP might not necessarily always indicate a stable eye. Stress testing, such as WDT, could therefore provide an additional layer of risk stratification, helping clinicians to decide who needs closer surveillance or earlier treatment escalation.
