Measuring Ocular Pulse Amplitude with Fixed Force Applanation on Normotensive and Hypertensive Eyes - PROJECT SUMMARY/ABSTRACT The measurement of intraocular pressure (IOP) is an integral part of the standard eye exam and elevated IOP is the greatest risk factor for the development of glaucoma, the most common cause of irreversible blindness. While the measurement of IOP, called tonometry, is frequently represented as a single number, the IOP is quite dynamic with pulsations due to the cardiac cycle: the IOP peaks during systole and troughs during diastole. The difference between the systolic and diastolic IOP is called the ocular pulse amplitude (OPA). Clinicians have long been aware of these ocular pulsations and the presence of these pulsations can make it difficult to measure the IOP: a large OPA is associated with significant IOP measurement variability. Fundamentally, the historical method of using a single, snapshot IOP to represent such a dynamic element, results in greater variability than desired and ignores much of the physiology of IOP and its effect on the eye. Prior studies have reported reduced OPA in eyes with glaucoma compared with controls and that reduced OPA was associated with worse glaucoma severity and a higher risk for glaucoma progression. Reduced OPA has been observed in biopsy-proven, giant cell artieritis, exudative age-related macular degeneration and diabetic retinopathy. While there are many preliminary studies that suggest the importance of OPA in the health of the eye, further study and has been hampered by the lack of devices to measure OPA. The rationale for this project is to develop a novel and validated method for measuring the OPA. This objective will be achieved by pursuing two specific aims: 1) validate applanation-based OPA measurements on nonhuman primates implanted with an IOP telemetry system in normotensive and hypertensive eyes; and 2) assess repeatability and reproducibility of OPA measurements in normotensive and hypertensive eyes. Under the first aim, the algorithm for two previously developed applanation-based tonometers will be modified to allow calculation of the OPA. Measurements with both devices will be acquired on implanted non-human primates and the device measurements will be compared to the telemetrically recorded values. Following algorithm optimization, a repeatability study with both devices will be conducted on normal and hypertensive eyes in the implanted nonhuman primates. Under the second aim, the previously optimized algorithm will be used first in a pilot study to assess proper performance in humans, followed by a study to assess the repeatability and reproducibility of both devices in normal and hypertensive human eyes. The proposed research is technically innovative because it proposes a novel technique for measuring the OPA using applanation that will be uniquely validated against manometrically-derived, ground truth IOP and OPA measurements. This innovation improves clinical care by improving reliability and accuracy of tonometry and opens new research horizons to allow improved understanding of the role of OPA in normal and abnormal ocular physiology.
