tests are somewhat unpractical and time-consuming; however, studies recently performed [26, 27–29] have shown that the water drinking test can predict IOP peak and possibly the likelihood of progression as well as treatment response. Since this kind of test is simple and safe, its clinical employment should deserve some attention in the future.

Summary for the Clinician

››IOP is usually higher at night due to increased episcleral pressure in the supine position.

››Physiologic compensations in perfusion and CSF changes probably compensates for the increase in IOP (this is not yet fully understood).

››There are differences in supine IOPs between younger and older individuals, as well as between healthy and glaucoma patients.

››Some reports show a correlation between office IOPs and nocturnal/supine peak in glaucoma patients and suggest that the peak value might be predicted by office measurements.

››Nocturnal IOP peaks may be estimated by taking diurnal IOP measurements in the supine position.

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