Transient intraocular pressure fluctuations: Source, magnitude, frequency, and associated mechanical energy

Abstract

PURPOSE. To characterize intraocular pressure (IOP) dynamics by identifying the sources of transient IOP fluctuations and quantifying the frequency, magnitude, associated cumulative IOP-related mechanical energy, and temporal distribution. METHODS. IOP was monitored at 500 Hz for periods of 16 to 451 days in nine normal eyes of six conscious, unrestrained nonhuman primates using a validated, fully implanted wireless telemetry system. IOP transducers were calibrated every two weeks via anterior chamber cannulation manometry. Analysis of time-synchronized, high-definition video was used to identify the sources of transient IOP fluctuations. RESULTS. The distribution of IOP in individual eyes is broad, and changes at multiple timescales, from second-to-second to day-to-day. Transient IOP fluctuations arise from blinks, saccades, and ocular pulse amplitude and were as high as 14 mm Hg (>100%) above momentary baseline. Transient IOP fluctuations occur ~10,000 times per waking hour, with ~2000 to 5000 fluctuations per hour greater than 5 mm Hg (~40%) above baseline. Transient IOP fluctuations account for up to 17% (mean of 12%) of the total cumulative IOP-related mechanical energy that the eye must withstand during waking hours. CONCLUSIONS. Transient IOP fluctuations occur frequently and comprise a large and significant portion of the total IOP loading in the eye and should, therefore, be considered in future studies of cell mechanotransduction, ocular biomechanics, and/or clinical outcomes where transient IOP fluctuations may be important. If IOP dynamics are similar in humans, clinical snapshot IOP measurements are insufficient to capture true IOP.