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R. E. Frenkel, M. Jaeger, R. Kline-Schroeder, M. A. Latina, J. M. Parel, M. P. C. Frenkel; Continuous Monitoring of Intraocular Pressure with an Implantable Device. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2858.
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To develop a non-contact device that will allow continuous monitoring of intraocular pressure during the patient’s normal daily routine. The system is based on the intraocular implantation of an extremely small, entirely passive transducer.
The transducer is a flexible structure that changes volume in response to changes in intraocular pressure. The transducer is an integrated module that consists of a parallel plate capacitor and a discrete inductor connected in series to form an L-C circuit. As the pressure surrounding the capacitor changes, the separation of the capacitor plates is varied and the resonant frequency of the L-C circuit changes. Non-contact pressure readings are made by measuring the resonant frequency of the coil using radio frequency (RF) energy from an external probe (grid-dip meter). The current system was designed with a target accuracy of 2 mmHg over a pressure range of 0-60 mmHg.
A 3 mm diameter prototype device was fabricated using silicon micro machining techniques. The capacitance change of the sensor was 7pF between 0 and 40 mmHg. The natural frequency varied from 37 MHz at 0 mmHg to 33 MHz at 40 mmHg. The IOP was measured by determining the resonant frequency of the sensor and was accurate to 2 mmHg. These frequency changes of the L-C circuit formed by the sensor yielded sufficient sensitivity to measure small changes in the pressure
We have demonstrated that a 3 mm in diameter continuous IOP sensor can be designed and fabricated by using silicon micro machining techniques that is accurate to 2 mmHg, to aid in the diagnosis and treatment of glaucoma.
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