Design of a Wireless Intraocular Pressure Monitoring System for a Glaucoma Drainage Implant

Abstract

Glaucoma is a common cause of blindness. Wireless, continuous monitoring of intraocular pressure (IOP) is an important, unsolved goal in managing glaucoma. An IOP monitoring system incorporated into a glaucoma drainage implant (GDI) overcomes the design complexity with incorporating a similar system in a more confined space within the eye. The device consists of a micro-electro-mechanical systems (MEMS) based capacitive pressure sensor combined with an inductor printed directly onto a polyimide printed circuit board (PCB). The device is designed to be placed onto the external plate of a therapeutic GDI. The resonance frequency changes as a function of IOP and is tracked remotely using a spectrum analyzer. A theoretical model for the reader antenna was developed to enable maximal inductive coupling with the IOP sensor implant, including modeling of high frequency effects. Pressure chamber tests indicate that the device has adequate sensitivity in the IOP range with excellent reproducibility over time. Additionally, we show that sensor sensitivity does not change significantly after encapsulation with polydimethylsiloxane (PDMS) to protect the device from the aqueous environment. In vitro experiments showed that the signal measured wirelessly through sheep corneal tissue was adequate indicating potential for using the system in human subjects.