Evaluation of applanation resonator sensors for intra-ocular pressure measurement: results from clinical and in vitro studies
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 IOPARS 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 IOPARS 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 &LE; 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.
applanation resonator sensor intra-ocular pressure eye piezo ceramics