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S. Fan, H. Liu, G. Zhan, L. J. Camras, D. Ghate, V. Gulati, C. B. Camras, C. B. Toris; Circadian Rhythms of Aqueous Humor Dynamics in Healthy Middle-Aged Humans. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1568.
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This study evaluates the circadian rhythms of aqueous humor dynamics in healthy middle-aged humans.
Thirty normal healthy volunteers (57.0±8.6 years; mean±SD) were enrolled in the study. Subjects were studied at one daytime and one nighttime visit. Measurements include central cornea thickness (CCT, µm) by pachymetry, intraocular pressure (IOP, mmHg) by pneumatonometry, aqueous flow (Fa, µL/min) by fluorophotometry, outflow facility by fluorophotometry (Cfl, µL/min/mmHg) and tonography (Cton), uveoscleral outflow by mathematical calculation (Fufl and Futon, µL/min) and seated systolic (SBP, mmHg) and diastolic (DBP) blood pressure by sphygmomanometry. Visits were compared by two-tailed paired t-tests. Daytime measurements only were made of episcleral venous pressure (Pev, mmHg) by venomanometry and anterior chamber depth (ACd, mm) by pachymetry. The position dependence of the tonometer probe oriented vertically and horizontally was tested in rabbit eyes at pressures set by manometry.
: Compared with daytime, nighttime Fa and Cton were reduced, CCT was increased, and uveoscleral outflow (Fufl and Futon) was unchanged. Compared with daytime seated IOP, nighttime seated IOP was reduced but supine IOP (habitual position) was increased (Table 1, means±SD, *P<0.001). The position of the tonometer probe in rabbit eyes (whether horizontal or vertical) did not affect the IOP measurement.
At night, this study shows an increase of CCT and supine IOP, and a decrease of Fa, C and seated IOP compared with daytime values. These findings indicate that some important ocular changes occur during the nocturnal period.
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