Water Drinking Test: New Insights into Myopia and Eye Pressure
"Uncover how the water drinking test reveals the choroid's role in intraocular pressure in myopic eyes."
Myopia, or nearsightedness, affects millions worldwide and is classified into low-to-moderate and high or pathological types. High myopia can lead to serious complications like macular atrophy and retinal detachment. These issues are often linked to the excessive elongation of the eyeball, causing a decrease in the thickness of the choroid, a vascular layer beneath the retina.
Recent advances in imaging technology, specifically spectral-domain optical coherence tomography (SD-OCT), have allowed for better visualization and measurement of the choroid. This improved imaging has opened new avenues for understanding how the choroid behaves under different conditions. One such condition is the water drinking test (WDT), typically used in glaucoma diagnostics, where patients consume a large amount of water in a short period.
While the WDT has been used to assess the eye's outflow facility reserve, its impact on choroidal thickness in myopic eyes remains less understood. A new study aims to evaluate how choroidal thickness changes during the WDT in individuals with high myopia compared to those with normal vision, shedding light on potential mechanisms affecting intraocular pressure (IOP).
IOP and Myopia in Focus
A 2026 systematic review describes growing interest in whether intraocular pressure (IOP)—the fluid pressure inside the eye—may contribute to myopia onset and progression in younger people. It examines possible biomechanical effects on ocular tissues, including the retina and choroid, and their links to axial elongation and scleral changes. Separately, a study found a statistically significant association between elevated IOP and high myopia, with elevated IOP observed more often in the high-myopia group than the medium-myopia group. The available sources establish no population-wide prevalence figure for this association.
Changing Ideas About Myopia
Historical accounts describe a long period of competing theories about myopia’s causes. From AD 1600 onward, authors warned against near work without sufficient pauses. One influential explanation held that near work required extra convergence, thickened the extraocular muscles, and elevated IOP; ocular tenotomies intended to treat myopia were also in vogue for a time. Axial lengthening was mentioned around 1700, but the historical account says it took about 150 years to become accepted as the most prevalent sign of myopia.
How Does Choroidal Thickness Vary in Myopic Eyes During the Water Drinking Test?
The study involved 30 participants, divided into two groups: those with high myopia (ME) and those with normal vision (EE). Participants underwent the WDT, and their choroidal thickness was measured using SD-OCT at baseline, 10 minutes, and 45 minutes after water ingestion. Researchers analyzed the average macular choroidal thickness and IOP changes during the test.
- Choroidal Thickness: Emmetropic eyes (EE) exhibited greater choroidal thickness compared to myopic eyes (ME) at baseline measurements.
- Water Drinking Test Response: Both EE and ME groups experienced significant changes in choroidal thickness, particularly at the fovea 10 minutes post-water ingestion.
- Intraocular Pressure Correlation: A moderate correlation was observed between IOP peaks during the WDT and choroidal thickness in ME.
Water Intake and IOP Research
A study of normal young Malaysian adults notes that IOP can fluctuate with factors including ingestion of water, posture, physical activity, time, and changes in accommodation. Another myopia study protocol advised participants to limit liquid intake for six hours before testing. Separately, a 2025 study set out to investigate myopia progression in three groups receiving different IOP-lowering medications: brinzolamide, latanoprost, and a third medication not named in the available source snippet. A 2026 study likewise set out to evaluate whether IOP-lowering medications slow axial elongation in adults with progressive high myopia; these study aims do not by themselves establish treatment effectiveness.
Causation Remains Uncertain
A 2022 review reports that a cross-sectional observational study found a positive correlation between IOP and high myopia. The review cautions that it is unclear whether IOP change causes myopia progression or results from it, and suggests IOP may instead be a contributing cofactor worth evaluating. It argues that directly studying the effects of IOP reduction could help clarify IOP’s role, while noting the need to control for adverse effects of IOP-lowering drugs in adolescents with myopia. High myopia is also associated with complications including glaucoma and heightened susceptibility to IOP elevation, adding clinical complexity to the relationship.
Comparing IOP Measurement Methods
A 2022 cross-sectional study compared intraocular pressure readings from Goldmann applanation tonometry (GAT) and non-contact tonometry (NCT). It enrolled 720 eyes from 720 Chinese adults with non-pathologic high myopia. The study’s stated purpose was to compare the values obtained by the two methods; the available source information does not report which method produced higher readings or the size of any difference.
Implications and Future Directions
The study's findings contribute to a better understanding of the relationship between myopia, choroidal thickness, and intraocular pressure. While choroidal thickness variations do not fully explain IOP elevations during the WDT, the study underscores the importance of considering choroidal characteristics in myopic eyes.
Unsettled Treatment Potential
A review highlights the close relationship between high myopia and glaucoma as a reason IOP’s possible role in high-myopia progression has attracted attention. It states, however, that whether lowering IOP can slow high-myopia progression remains unclear. This uncertainty leaves the potential of IOP reduction as a myopia-control approach unresolved.
Water-Drink Testing and a Long-Term Case
A study of highly myopic eyes during the water drinking test measured average macular choroidal thickness using spectral-domain optical coherence tomography (SD-OCT) and measured IOP. A separate 2024 case report described severe myopia reversing after 24 years of hypotony, with axial length reduced by more than 2 mm and refractive stability continuing for two years after IOP normalization. The report also noted that ocular signs of pulmonary hypertension preceded cardiovascular signs by two decades. These findings describe a study’s measured outcomes and a single case, not a general treatment effect.
Future research should explore other factors influencing IOP during the WDT, such as aqueous humor dynamics and outflow facility, to provide a more comprehensive understanding of IOP regulation in myopic eyes. Additionally, longitudinal studies could investigate the long-term effects of choroidal thickness changes on visual outcomes in individuals with high myopia.
By continuing to investigate the complex interplay between myopia, choroidal health, and intraocular pressure, researchers can develop targeted interventions to prevent vision-threatening complications and improve the quality of life for individuals with myopia.