Novel implantable capacitive inductive pressure sensor for continuous wireless intraocular pressure monitoring

Abstract

 

Purpose

 

To present the concept of and pilot results for a novel implantable passive sensor enabling wireless measurement of intraocular pressure (IOP).

 

Methods

 

The sensor comprises a flexible diaphragm chamber integrated with a variable inductor (coil) and capacitor in the top layer and a metal plate (ferrite or copper) in the bottom layer. Pressure induces a mechanical deflection of the bottom layer and inner diaphragm, thereby altering the magnitudes of the inductance and capacitance. The resultant change of resonant frequency (RF) is then detected by an external reader. The sensor was tested in a customized pressure jig with air pressurization, after which it was implanted into the anterior chamber of a rabbit eye to measure the RF response to IOP elevation. The biocompatibility of the sensor was evaluated by serial microscopic and histological examinations of the enucleated rabbit eye sixteen weeks post-implantation.

 

Results

 

The in-vitro measurement showed a significant RF shift (i.e. 81.50 MHz - 78.90 MHz; total: 2.60 MHz) with increasing pressure (i.e. from 0 mmHg to 40 mmHg) in the jig. The in-vivo measurement also showed a negative RF shift (i.e. 46.90 MHz - 46.55 MHz; total: 0.35 MHz), this time as the result of an IOP increase (i.e. from 6.3 mmHg to 25.8 mmHg) induced by 12 minutes’ infusion of a balanced salt solution into the anterior chamber (Figure 1). The microscopic in-vivo evaluations and histological exam, all performed at sixteen weeks post-implantation, showed no evidence of significant inflammation or foreign-body reaction.

 

Conclusions

 

This novel capacitive inductive sensor for continuous wireless monitoring of IOP was validated both in an in-vitro test and in a rabbit eye, where it was well tolerated.

 

 

Figure 1. In vivo measurement of resonant frequency with elevation of intraocular pressure.

 

Keywords: 568 intraocular pressure