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Barbara Junghans, Chia-Jung Chang, Angela Siu, Natalia Soesanto, Megan Tu, Melanie Murphy, Sheila Crewther; Intraocular Pressure in Myopic Eyes during the Water Drinking Test. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1912.
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The rapidly increasing prevalence of myopia worldwide has been linked to increasing complexity of modern urban lifestyles. In addition, animal as well as pilot human studies have suggested that stress-induced physiological dysregulation of trans-retinal fluid outflow may play a role in ocular growth and the enlarged myopic eye. Thus, this study aimed to investigate differences between myopes and non-myopes in ocular fluid regulation and cortisol levels after the rapid ingestion of water.
Forty-one healthy adults of mean age 22.6±1.6yrs were randomly assigned either to a control group or to drink 1 liter of water over 10mins. Refractive error (Shin Nippon open-field autorefractor), intraocular pressure (IOP) (Tonopen), central corneal thickness (Sonogage), axial length, anterior chamber depth (IOL Master) and salivary cortisol (Salivettes) were measured at baseline, T=20 and T=40mins. Twenty-five subjects were myopes (mean -3.50±2.00DS).
As expected, myopic eyes were significantly longer (p<0.01). Water loading caused a significant increase in IOP by T=20 (3.9±0.6mmHg) that was similar for both refractive subgroups. However, IOP returned to within normal range by T=40 in non-myopes whereas for myopes the increased levels of IOP remained until at least T=40 (p<0.001). No significant associations were observed between water loading and central corneal thickness, axial length, anterior chamber depth or salivary cortisol.
The Water Drinking Test itself was not sufficiently stressful to show significant change in cortisol levels that may indirectly affect fluid regulation within the eye. However, myopes demonstrated altered ocular fluid dynamics which could suggest that myopic eyes have reduced ocular fluid regulation. This fluid dysregulation may indirectly influence volumetric enlargement of the globe.
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