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J. Downs, C. F. Burgoyne, Y. Liang, V. L. Sallee; A New Implantable System for Telemetric IOP Monitoring in Nonhuman Primates (NHP). Invest. Ophthalmol. Vis. Sci. 2008;49(13):2043.
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To develop and test a new system for accurate, long-term, low-drift, high sample rate, continuous telemetric IOP monitoring in NHPs.
We have adapted a proven implantable telemetric pressure transducer system (T30F, ITS, Dexter, MI) to monitor IOP by integrating the transducer into a custom, Baerveldt-style baseplate that is connected to the anterior chamber via a silicone tube. An implanted transmitter sends 500 IOP, ECG and body temperature measurements per second to an external antenna. Data is acquired with a commercially available system equipped with real-time barometric pressure compensation (ITS). We tested transducer accuracy from 5-60 mm Hg by cannulating the anterior chamber with a 27-G needle connected to an adjustable saline reservoir equipped with an in-line digital manometer. At six weeks post op, we recorded IOP during these calibration checks, Tonopen IOP readings, and several 96-hour periods of undisturbed normal activity.
We have successfully implanted the system in one NHP, and the implant healed in with no complications. While the globe appears slightly inferiorly displaced in primary gaze, eye movement is unimpeded and the animal is behaving normally. Manometer tests confirm that the IOP transducer is accurate to within 1 mmHg from 5-60 mmHg. The transducer measured an ocular pulse of ~1 mmHg at IOPs higher than 30 mmHg, registers transient IOP elevations up to 20 mmHg in response to corneal Tonopen contact, and recorded frequent IOP fluctuations of up to 40 mmHg above baseline during normal animal activity (Figure).
We have successfully measured IOP continuously using a new IOP telemetry system that has very good accuracy, no signal dropout, low drift (<3 mmHg/month), and battery life of at least 2 years of continuous use (up to 5 years intermittent). Further, since the transducer sits on the eye, artifacts due to head movement are minimized and the system is sensitive to transient IOP elevations as short as 50 msec. Finally, IOP fluctuates tremendously during normal activity, which indicates that snapshot measurements are not adequate to capture the true dynamic character of IOP.
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