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J Crawford C Downs, Christopher A Girkin, Brian C Samuels; Testing and Validation of a New IOP Telemetry Sensor Suitable for Implantation Directly into the Anterior Chamber. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1598.
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© ARVO (1962-2015); The Authors (2016-present)
To test and validate a new piezoelectric pressure sensor implanted directly in the anterior chamber of nonhuman primates as a platform for IOP telemetry.
We have developed and validated an implantable telemetry system (Konigsberg Instruments; KI) that wirelessly records 500 IOP measurements per second continuously for up to 2-1/2 years (IOVS 52(10):7365-75). The KI system was based on a large, 6-mm-diameter pressure transducer that was screwed into a hole drilled into the orbital wall, and IOP was transmitted to the transducer via an aqueous-filled silicone tube inserted into the anterior chamber. The implant was large, and the battery required intraperitoneal placement. We have developed an updated bilateral IOP and ocular perfusion pressure (OPP) telemetry system based on the TSE Systems Stellar platform, that uses small 4-mm-long, 400-µm-diameter piezoelectric pressure transducers that can be implanted directly in the anterior chamber and carotid artery lumen (Figure). IOP was continuously recorded at 200 Hz for 15 seconds of every 150 second period in 4 eyes of 3 adult male rhesus macaques. The IOP sensors were calibrated via anterior chamber manometry every 2 weeks to assess signal drift, and physiologic IOP was evaluated for dynamic accuracy and sensitivity.
Over the course of two months, IOP showed dynamic transients in response to systolic vascular filling, blinks, saccades, and corneal applanation tonometry with a Tonopen XL (Figure) that are consistent with measurements using our previous telemetry system. IOP transients from Tonopen applanation measured with the telemetry sensor matched those measured directly via anterior chamber cannulation with an external PowerLab pressure monitoring system. IOP transducer drift was 1-4 mmHg per month after heal-in, and the sensor was linear and accurate from 5-45 mmHg.
Results show that a new piezoelectric pressure transducer, small enough to be implanted in the anterior chamber of the human eye, is capable of accurately measuring mean IOP and IOP transients near-continuously over long periods, with low power requirements and signal drift. Such a sensor could be inductively powered, and may be translatable for human use via surgical implantation.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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