Effects of Aging on 24-Hour Intraocular Pressure Measurements in Sitting and Supine Body Positions

Abstract

PURPOSE.To evaluate how aging alters 24-hour measurements of intraocular pressure (IOP) in the sitting and supine body positions. METHODS. Fifteen older volunteers with healthy eyes (ages, 53-71 years) were each housed for 1 day in a sleep laboratory. An 8-hour accustomed sleep period was assigned to each subject. Every 2 hours, measurements of IOP were taken in the sitting and supine positions. Sitting and supine patterns of 24-hour IOP were compared. Simulated 24-hour IOP rhythms in the same body position were determined using cosine fitting of individual 24-hour data. The average postural IOP effects during the diurnal/wake period and the nocturnal/sleep period were compared. Data from this group of older subjects were compared with previously collected data from 16 healthy younger subjects (ages, 18 -25 years) under the same experimental conditions. RESULTS. Within each age group, sitting and supine patterns of 24-hour IOP were similar and parallel. Compared to the younger subjects, the phase timing (simulated peak) of 24-hour IOP was significantly delayed for the older subjects in both body positions. The postural IOP effect for the older subjects was 4.7 Ϯ 0.8 and 4.8 Ϯ 0.8 mm Hg during the diurnal and nocturnal periods, respectively. These postural IOP effects were not significantly different from the postural effects in the younger subjects. CONCLUSIONS. Although aging can significantly delay the phase timing of the 24-hour IOP pattern toward the diurnal/awake period, it may not affect the postural IOP effect during the diurnal and the nocturnal periods. (Invest Ophthalmol Vis Sci. 2012;53:112-116) DOI:10.1167/iovs.11-8763 I ntraocular pressure (IOP) in the human eye is regulated by the rate of aqueous humor formation, the resistance of aqueous humor outflow, and the episcleral venous pressure. IOP varies throughout a 24-hour period due to changes in these physiologic parameters. In healthy younger and nonmyopic subjects, there is 24-hour variation of IOP with a peak value in most individuals occurring in the late nocturnal/sleep period in either sitting or supine body position, independent of posture.1,2 Postural IOP effects, the difference in IOP between the sitting and supine body positions, are not significantly different between the diurnal and nocturnal periods.1 However, an earlier study indicated that the 24-hour IOP variation in the aging population may be different from that in the younger subjects. 3Changes in 24-hour IOP measurements may occur because of age-related structural or functional changes, including alterations in hormonal and neural activities for the regulation of IOP. Circulating levels and timing of glucocorticoids and melatonin as well as the neuronal activities such as the baroreflex may affect the IOP pattern and its variation within a 24-hour period.4 -8 A reported age-related change is the postural IOP effect, 9,10 which is associated with the hydrostatic response in the episcleral venous pressure and the redistribution of body fluid including the choroidal vascular volume...

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