Objective: Reduction and diurnal stabilization of the intra-ocular pressure (IOP) is the mainstay
of treatment for glaucoma. Fluctuations of IOP in glaucomatous patients can also be induced
by the osmotic variations caused by water ingestion. Such influence can be studied by
means of the water-drinking test (WDT). The aim of this study was to perform the WDT in
patients with primary open-angle glaucoma (POAG) while they were being treated with different
IOP-lowering medications, to test the effect of drugs with different mechanisms of action
on the ability to maintain a stable IOP.
Methods: A total of 280 POAG patients were enrolled, 40 patients per group for each of the
tested medications (timolol, dorzolamide, brinzolamide, travoprost,latanoprost, bimatoprost,
and brimonidine). After baseline IOP measurement, all patients underwent WDT (1000 mL
of water in 10 min). The IOP was measured at 15-min intervals until the return of IOP to baseline
values. The main outcomes measured were mean IOP peak, mean IOP percentage increase,
and mean time for returning to baseline IOP value.
Results: The highest mean IOP peak was found with timolol, whereas no difference was
found among the other drugs. The highest mean IOP percentage increase was found with timolol,
whereas bimatoprost showed an IOP percentage increase significantly lower than latanoprost,
dorzolamide, and brinzolamide. The duration of IOP increase was shortest for bimatoprost
and longest for timolol.
Conclusion: This study suggests that topical medications that enhance outflow (e.g., bimatoprost,
latanoprost, travoprost, and brimonidine) may provide, under stressful conditions
such as the WDT, better IOP stabilization than medications that decrease aqueous humor inflow,
such as timolol and topical carbonic anhydrase inhibitors.
