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J. H. K. Liu, T. Kida, R. N. Weinreb; Twenty-Four-Hour Corneal Biomechanical Changes in the Aging Population and Their Influences on Intraocular Pressure Measurement. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3939.
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It was reported that 24-hour change pattern of intraocular pressure (IOP) in healthy young adults (age 20-25 years) was not associated with a 24-hour change in known corneal biomechanical properties. The present study determined 24-hour changes in corneal biomechanical parameters in a group of older volunteers and their influences on the measurement of IOP.
Twelve older volunteers with healthy eyes (age 50-80 years) were housed for one day in a sleep laboratory with 16-hour diurnal/wake period and 8-hour nocturnal/sleep period. Central corneal thickness (CCT) was measured every two hours using an ultrasonic pachymeter in the sitting position. Corresponding sitting IOP and corneal hysteresis, an indicator of corneal viscoelasticity, were measured in the same eye using a non-contact tonometer.
There were consistent 24-hour variations of CCT and IOP for the group. The nocturnal mean CCT was significantly higher than the diurnal mean CCT. The nocturnal mean IOP was significantly lower than the diurnal mean IOP. The peak CCT occurred at 5:30 AM and the trough CCT at 11:30 AM. The peak IOP occurred at 9:30 AM and the trough IOP at 11:30 PM. Cosine-fits of individual’s 24-hour CCT and IOP data showed synchronized rhythms. The phase timing of 24-hour CCT rhythm was significantly earlier than the phase timing of 24-hour IOP rhythm. Twenty-four-hour variation of corneal hysteresis was inconsistent and cosine-fits of 24-hour data of corneal hysteresis did not display a 24-hour rhythm.
In this group of older volunteers with healthy eyes, CCT was thicker and sitting IOP was lower during the nocturnal period than during the diurnal period. Peak CCT occurred significantly earlier than peak IOP. Twenty-four-hour change of corneal viscoelasticity was not significant. Similar to the result obtained in healthy young adults, there was no evidence that 24-hour change pattern of IOP in the aging population is associated with a change in corneal biomechanical properties.
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