Implantable wireless microsystems for the measurement of intraocular pressure

Wireless microelectronic systems designed for implantation within the eye are being developed to enable non-contact, high-accuracy and continuous recording of intraocular pressure (IOP). These microsystems will revolutionize the treatment and understanding of glaucoma by increasing the frequency and accuracy of IOP measurements. Past development of such systems has been focused on Radio Frequency (RF) based, transistor-less, resonant LC-tank systems, utilizing capacitive pressure sensors. However, complex external-wireless interfaces have limited implementation. To address this, RFID-based passive radio architectures incorporating DAQ systems and MEMS pressure sensors have been developed. One such system, using a load-modulated bi-directional RFID reader combined with a custom RFID transponder composed of a MEMS pressure sensor, FRAM memory chip, and mixed-signal CMOS, has been demonstrated, but is limited to 2.5 cm read range. A new 915 MHz system under development extends operating range closer to 100 cm. Power is derived from an energy harvesting system containing a RF-to-DC converter and a voltage multiplier circuit connected to a voltage regulator. An oscillator tied to the pressure sensor performs pressure sensing in real time. The electrically small antenna fits into an area less than 10mm by 10mm. (Wireless implant, intraocular pressure sensor, glaucoma).