Performance of implantable inductive pressure sensor for continuous monitoring of intraocular pressure

Abstract

 

Purpose

 

To validate the performance and biocompatibility of a novel implantable inductive pressure sensor for continuous monitoring of intraocular pressure (IOP).

 

Methods

 

The novel implantable IOP sensor is composed of a top layer integrated with an inductor and capacitor circuit and a bottom layer integrated with ferrite. With IOP change, a mechanical deflection of the sensor’s bottom layer is effected, which changes the distance between the bottom-layer ferrite and top-level inductor, resulting in an alteration of inductance magnitude. Thereby, the resonant frequency (RF) undergoes an alteration, which is detected by an external reader. For a prototype larger-sized sensor, in-vitro measurement was conducted by means of air pressurization in a sealing jig. Subsequently the sensor was implanted into the anterior chamber of a rabbit eye and anchored at the juxtalimbal sclera under the scleral flap. In-vivo measurement was then conducted while IOP was elevated by infusion of a balanced salt solution (BSS). Second-generation smaller-sized sensors were later implanted into two rabbit eyes, which were microscopically examined at two, four, and eight weeks post-implantation. The eyes were then immediately enucleated preparatory to a histological exam.

 

Results

 

The in-vitro measurement showed a significant shift of RF, from 10.42 MHz to 9.75 MHz, as pressure in the jig was increased from 0 mmHg to 20 mmHg. The in-vivo measurement also showed that over the span of 10 minutes, the RF decreased from 12.80 MHz to 12.67 MHz (total shift: 0.13 MHz) as the BSS was infused at the rate of 6µl/min (Figure 1). The microscopic in-vivo evaluations and histological exam, performed at intervals up to eight weeks post-implantation, showed no evidence of significant inflammation or deformity of the ocular-tissue structures.

 

Conclusions

 

The prototype implantable IOP sensor demonstrated both the feasibility of wireless pressure sensing and favorable biocompatibility.

 

 

Figure 1. In vivo measurement of resonant frequency during infusion of a balanced salt solution

 

Keywords: 568 intraocular pressure