A wireless, low-drift, implantable intraocular pressure sensor with parylene-on-oil encapsulation

This paper presents a wireless, implantable continuous intraocular pressure (IOP) monitoring system that features a parylene-on-oil sensor encapsulation method for achieving long-term low-drift in vivo. The system is implanted in the superotemporal quadrant of the eye between the sclera and conjunctiva. It consists of a commercial pressure sensor (STMicroelectronics LPS25H) with digital readout, a 65nm CMOS chip that supports wireless power/data telemetry and the I2C serial communication interface with the pressure sensor. The chip and pressure sensor are assembled on a flexible polyimide PCB, and then the sensor is submerged in biocompatible silicone oil and coated with parylene in situ. The implant uses an on-chip integrated RF coil to receive power from near-field RF coupling at 915 MHz and transmit measurement bits via RF-backscattering to an external reader. A 2 mm × 1.2 mm chip is fabricated in TSMC 65nm CMOS process. The IOP implant achieves a pressure sensitivity of 0.17 mmHg with a total power consumption of 9.7μW. We demonstrate pressure offset drift of less than 0.5 mmHg for more than 4 months over a temperature range of 27–38 °C. The implant successfully tracks induced IOP variations in a porcine eye ex vivo, validating the system functionality and surgical implantation.