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J. H. K. Liu, R. N. Weinreb; Influence of Aging on the Postural Intraocular Pressure Effect During the Nocturnal Period. Invest. Ophthalmol. Vis. Sci. 2010;51(13):561.
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Intraocular pressure (IOP) decreases when one changes body position from supine to sitting. Influence of aging on this postural IOP effect was examined in healthy eyes during the diurnal/wake period and the nocturnal/sleep period.
Fifteen older volunteers with healthy eyes (ages, 53-71 years) were housed for one day in a sleep laboratory with 16-hour diurnal/wake period and 8-hour nocturnal/sleep period. Every two hours, measurements of IOP were taken using a pneumatonometer after 5 minutes in the supine position and 5 minutes in the sitting position. The postural IOP effects were averaged for the diurnal period and for the nocturnal period. Cosine fittings of each subject’s 24-hour IOP data in the same body position were performed. The phase timing and IOP fluctuation were determined using the simulated 24-hour IOP rhythm. Data from this older group were compared with data collected from a group of 16 younger healthy subjects (ages, 18-25 years) under the same experimental conditions.
For the older group, the postural IOP effect was 4.74 ± 0.78 mmHg (mean ± SD) during the diurnal period and 4.75 ± 0.82 mmHg during the nocturnal period. There was no significant difference between the diurnal and nocturnal postural IOP effects (P=0.961). For the younger group, the postural IOP effects were 4.28 ± 1.51 mmHg and 3.89 ± 2.29 mmHg for the diurnal and nocturnal periods, respectively (P=0.457). The postural IOP effects in the older group were not statistically different from those effects in the younger group during the diurnal period (P=0.300) and during the nocturnal period (P=0.180). Cosine-fits showed synchronized 24-hour IOP rhythms for the older group as well as for the younger group. Phase timings were 10:20 AM ± 205 min in the sitting position and 10:23 AM ± 268 min in the supine position for the older group. Phase timings were 6:35 AM ± 202 min and 5:31 AM ± 211 min for the younger group in the sitting and supine body positions, respectively. Compared to younger subjects, older subjects had significantly delayed 24-hour IOP phase timings in the sitting position (P=0.004) and in the supine position (P=0.002). Simulated 24-hour IOP fluctuations showed no difference between the older and younger groups in either body position.
While aging significantly delays phase timing of the 24-hour IOP rhythm toward the diurnal/wake period, aging does not significantly affect the postural IOP effect during the diurnal/wake period or during the nocturnal/sleep period.
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