A resonator sensor for measurement of intraocular pressure - evaluation in anin vitropig-eye model

Abstract

Intraocular pressure (IOP) measurement is performed routinely at every eye clinic. High IOP, which can be a sign of glaucoma, can lead to degeneration of the retina and can cause blindness. In this study we developed a resonator sensor for IOP measurement based on an oscillator consisting of a piezoelectric element made of lead zirconate titanate, a flat contact piece of nylon and a feedback circuit. The aim of this study was to evaluate the new sensor's ability to determine lOP in an in vitro pig-eye model. Six eyes from four pigs were removed and fixed in agar. They were then pressurized by a saline column (10-35 cm H2O) through a cannula inserted into the vitreous chamber. The IOP was measured with the resonator sensor applied to cornea. An Alcon applanation pneumatonometer and a standard Viggo-Spectramed pressure sensor connected to the saline column were used as references. The IOP as measured with the resonator sensor correlated well with the pressure elicited by the saline column for individual eyes (r = 0.96-0.99, n = 60) and for all eyes (r = 0.92, n = 360). The correlation between the resonance sensor and the pneumatonometer was r = 0.92 (n = 360). The pneumatonometer also showed a good correlation with the saline column (r = 0.98, n = 360). We conclude that our in vitro pig-eye model made it possible to induce reproducible variation in IOP, and measurement of that pressure with the newly developed resonator sensor gave very promising results for development of a clinically applicable IOP tonometer with unique properties.

The influence of intraocular pressure on the damping of a coupled speaker–air–eye system

“…The effect is known from current tonometry methods such as the iCare tonometer (Munkwitz et al, 2008), Tono-pen (Giaconi et al, 2016), or air-puff tonometers (Derka, 1980) that the sensitivity decreases at higher IOP levels (Yung et al, 2014;Giaconi et al, 2016;Eklund et al, 2000). This is explained by the fact that the possible deformation of the eye with a constant force decreases, which leads to a lower signal-to-noise ratio.…”

Evaluation of applanation resonator sensors for intra-ocular pressure measurement: Results from clinical andin vitro studies

“…First, a clinical evaluation of the same resonator sensor probe that was used in a previous in vitro study (EKLUND et al, 2000) was performed. Secondly, the same probe was used in an in vitro pig-eye model, where its sensitivity to off-centre positioning was investigated.…”

“…That study suggested that the larger the contact area, the more vibrational energy is transferred to the sample, thereby increasing the influence of the sample on the frequency characteristics of the sensor system, resulting in a larger frequency shift. In a later study (EKLUND et al, 2000), that argument was extended, modelled and verified for the applanation resonator sensor (ARS), by showing the relationship between a linear phase shift of the sensor element AqbsE and the resulting frequency shift of the sensor system Ajs. The relationship is based on a resonance condition that states that the sum of phase shift around the circuit must be zero and an assumption that AqbsE is a linear function of contact area.…”

“…Recently, a new sensor for lOP measurement, the applanation resonator sensor (ARS), was presented (EKLUND et al, 2000) and evaluated in an in vitro pig-eye model. The sensor is based on a piezo-electric element that is set to vibrate with its resonance frequency, it was shown that the ARS could be used to measure lOP in a physical model.…”

A FEM-based method using harmonic overtones to determine the effective elastic, dielectric, and piezoelectric parameters of freely vibrating thick piezoelectric disks

“…It has been shown that these sensors can distinguish between normal and cancerous prostate tissue, and could therefore constitute a new diagnostic instrument [1]. Moreover, such sensors can be used to measure the intra-ocular pressure, providing information for the evaluation of edema [2], [3].…”