Development of a wireless intra-ocular pressure monitoring system for incorporation into a therapeutic glaucoma drainage implant

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 associated 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 integrated with an inductor printed directly onto a polyimide printed circuit board (PCB). The device is designed to be incorporated 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. Pressure chamber tests indicate that the sensor implant 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 fluid environment. In vitro experiments showed that the signal measured wirelessly through sheep corneal and scleral tissue was adequate indicating potential for using the system in human subjects.