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J Crawford C. Downs, Claude F. Burgoyne, William P. Seigfreid, Juan F. Reynaud; IOP Telemetry In Non-human Primates: Characterization Of Continuous IOP At Multiple Time Scales. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1649.
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IOP is the most common independent risk factor for development and progression of glaucoma, but very little is known about the dynamics of IOP. We used IOP telemetry in three awake, unrestrained non-human primates to characterize the dynamics of IOP over multiple time scales for multiple 24-hour periods.
We have adapted a proven implantable telemetric pressure transducer system to monitor IOP by integrating the transducer into a orbital wall-mounted baseplate that is connected to the anterior chamber via a silicone tube. The total implant system is surgically implanted and all components are internal to the animal. The implanted transmitter sends 500 IOP, ECG and body temperature measurements per second to an external antenna, and the system compensates for barometric pressure in real time. The continuous IOP signal was filtered for noise/dropout, then averaged using a time window averaging technique for nineteen, eighteen, and four 24-hour periods in three non-human primates, respectively. Those data were then statistically analyzed for a nycthemeral pattern within each animal.
IOP fluctuates as much as 10 mmHg day-to-day and hour-to-hour when measured continuously via telemetry in unrestrained, awake non-human primates. 10-minute time window averaging for a 24-hour period shows that IOP fluctuates from 7-14 mmHg during the day, and those changes occur frequently and quickly. 2-hr time window averages for multiple 24-hour periods in 3 animals show that IOP follows no particular nycthemeral rhythm.
We have successfully measured IOP continuously using a new, fully implantable IOP telemetry system that has demonstrated high accuracy and low drift (<3 mmHg/mo). IOP fluctuates tremendously in the non-human primate, which agrees with the most recent human studies on 24-hr IOP variation and indicates that snapshot IOP measurements may be inadequate to capture the true dynamic character of IOP. In addition, IOP fluctuations of this magnitude could be an important yet unknown contributor to IOP-related glaucomatous damage.
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