Precision Wireless Implantable Continuous Intraocular Pressure Sensors Utilizing Parylene-on-oil Encapsulation

Abstract

Purpose : To demonstrate the precision of a first of its kind fully implantable continuous wireless pressure sensor that measures true intraocular pressure (IOP) and leverages commercially fabricated microelectromechanical (MEMS) components with embedded temperature compensation to ensure superb reliability. Methods : The continuous IOP sensor, with a form factor similar to an aqueous shunt, is designed to be implanted with the electronics in the superotemporal or inferotemporal subtenon's space with a flexible 23-gauge silicone tube permanently inserted into the anterior chamber or the pars plana. It consists of a parylene-on-oil packaged LPS25H MEMS barometer with temperature compensation (STMicroelectronics, Geneva, Switzerland), capacitors, and a custom designed integrated circuit, all assembled on a flexible polyimide substrate. Devices were tested on the benchtop. Ex vivo porcine eyes were vitrectomized, and the IOP sensor tube placed into the pars plana through one of the sclerotomies. The IOP was varied using the pressure setting on the vitrector, and resultant pressure readings from the sensor were analyzed. Results : Photographs of the fabricated device are shown in Fig. 1(a-b).1 In air, the wireless device has demonstrated 0.17 mmHg pressure sensitivity. Accelerated-lifetime saline soak testing of the packaged barometer itself has demonstrated stability for an extrapolated 20 months to date. A photograph of the ex vivo wireless porcine eye setup is shown in Fig. 1c. In addition to excellent precision during IOP sweeps, a step from 5 to 75 resulted in a 69.92 mmHg change as measured by the sensor (Fig. 2). A slow ramp down after changing the setting on the vitrector back to 5 mmHg is seen because the eye is essentially a closed system. Conclusions : A breakthrough wireless IOP sensor has been realized utilizing a commercially fabricated barometer and a custom integrated circuit as its backbone. All testing to date, including ex vivo porcine data, demonstrates superior reliability and precision.