Measuring Real-Time Corneal Elasticity Standardized to Intraocular Pressure

Abstract

Purpose : Validate a simple and quick method for measuring standardized corneal elasticity in live subjects using a multicenter randomized clinical trial.

Methods : A recently developed modified surface Goldmann tonometer (GAT) prism has shown promise to correct intraocular pressure (IOP) measurements for central corneal thickness (CCT) and corneal hysteresis (CH) without overall IOP bias. The difference between a modified surface (centrally concave) and standard flat surface GAT prism's IOP measurement is a direct measurement of the biomechanical “bendability” of the cornea. Therefore, the modified/standard GAT difference is likely an IOP standardized real-time measure of corneal elasticity. In order validate this hypothesis, a GAT and a modified surface GAT prism were used to measured IOP on 243 unique eyes. The study design and analysis complied with FDA 510(k) and ANSIZ80.10-2014 guidelines, except the inclusion of thin (<500µm) and thick (>600µm) corneas. All eyes were randomized to IOP measurement by one of 5 standard Goldmann prisms or 5 modified prisms. Pressures were measured by 6-investigators, 2-times with each prism for a total of 1936 IOP measurements. Analysis included a multiple linear regression for CCT and CH correlation to the modified/standard GAT IOP difference.

Results : The difference in IOP measurements of the standard and modified Goldmann prisms correlated well to CCT particularly in thin (<500µm) and thick (>600µm) corneas (R²=0.404, p=0.007). Corneal hysteresis (CH) also correlated well to the difference in prism measurements (R²=0.125, p=0.039). The overall mean bias between two prisms was +0.32mmHg in the modified prism (p=0.29).

Conclusions : The difference in measured IOP between the modified surface and standard surface prisms indicated a statistically significant correlation to CCT, similar to the recognized Dresdner correction. A similar finding demonstrates significant CH correlation, without overall bias. The expected correlation to known real-time corneal biomechanical metrics promotes validation that the Modified/Standard GAT difference is an IOP standardized measurement of the static metric of corneal elasticity. The potential research opportunities of a real-time measured corneal elasticity are extensive, similar to corneal hysteresis.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Standard flat applanating surface Goldmann prism (above) and modified centrally concave and annularly convex prism (below)