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

Abstract

Glaucoma is an eye disease that, in its most common form, is characterised by high intra-ocular pressure (IOP), reduced visual field and optic nerve damage. For diagnostic purposes and for follow-up after treatment, it is important to have simple and reliable methods for measuring IOP. Recently, an applanation resonator sensor (ARS) for measuring IOP was introduced and evaluated using an in vitro pig-eye model. In the present study, the first clinical evaluation of the same probe has been carried out, with experiments in vivo on human eyes. There was a low but significant correlation between IOP(ARS) and the IOP measured with a Goldmann applanation tonometer (r = 0.40, p = 0.001, n = 72). However, off-centre positioning of the sensor against the cornea caused a non-negligible source of error. The sensor probe was redesigned to have a spherical, instead of flat, contact surface against the eye and was evaluated in the in vitro model. The new probe showed reduced sensitivity to off-centre positioning, with a decrease in relative deviation from 89% to 11% (1 mm radius). For normalised data, linear regression between IOP(ARS) and direct IOP measurement in the vitreous chamber showed a correlation of r = 0.97 (p < 0.001, n = 108) and a standard deviation for the residuals of SD < or = 2.18 mm Hg (n = 108). It was concluded that a spherical contact surface should be preferred and that further development towards a clinical instrument should focus on probe design and signal analysis.

Prostate tissue stiffness as measured with a resonance sensor system: a study on silicone and human prostate tissue in vitro

“…The resonance sensor has also been studied [3] for the measurement of intraocular pressure (IOP) of the eye to detect glaucoma. Measurements on pig eyes in vitro correlated well with the IOP [5]. Further development of the sensor system showed that a spherical contact surface was preferred because that made the sensor less dependent on variations in surface topography.…”

“…A hemi-spherical tip will not subject the object to as large forces as a flat one of same diameter, at a certain impression depth. Also, Eklund et al [5] concluded that a spherical tip is preferred instead of a flat tip because off-center loads of the sensor tip would be avoided. These off-center loads could be received due to an irregular or inclined surface when measuring on prostate tissue.…”

Change in Intraocular Pressure Measurement After Myopic LASEK

“…This frequency shift is proportional to the contact area. 21 A force transducer measures the force needed to applanate the cornea. Both contact area and force are sampled continuously with a 1 kHz sampling rate.…”

Symmetric sensor for applanation resonance tomometry of the eye

“…There were six repeated measurements on five different positions, centre position and four 1.0 mm off-centre positions (at 3, 6, 9, and 12 o'clock on the cornea) [5,6].…”