Experimental and Numerical Analysis of Ocular Tactile Tonometry

Abstract

This article describes the experimental and numerical analysis of a novel trans-scleral tonometer based on the use of an instrumented form of digital palpation tonometry. Similar to manual digital palpation tonometery (estimation of the eye pressure via tactile touch), the novel ocular tactile tonometer utilizes multiple force probes to gather force data from indentation experiments. The presented experimental and numerical analysis shows that force data obtained from these probes correlate with the intraocular pressure (IOP) of the eye. Enucleated porcine eyes were used to validate the approach. The observed hysteresis in the force data was analyzed using an analytical model that accounts for the outflow of the aqueous humor as well as experiments at different indentation rates. Experimental data from eye distention and indentation tests were then used to infer the conditions under which the novel tonometer would be expected to have an accuracy of 1 mmHg. Analysis of the data shows that visco-elastic behavior of the scleral tissue is the primary factor responsible for the observed hysteresis. Further analysis of the data shows that indentation rates should be kept below 0.5 mm/sec for a pressure range of 10–35 mmHg. A conceptual through-the-eye-lid ocular tactile tonometer based on four probes is also presented along with numerical validation of the measured response.