Modified Goldmann prism intraocular pressure measurement accuracy and correlation to corneal biomechanical metrics: multicentre randomised clinical trial

Abstract

Purpose: Clinically evaluate intraocular pressure (IOP) measurements taken with a Goldmann applanation tonometer (GAT) prism and a modified surface Goldmann prism examining measurement differences correlated to central corneal thickness (CCT) and corneal hysteresis (CH) values.

Design: Prospective, open-label, randomised, controlled, multicentre reference device accuracy analysis.

Methods: A GAT and a modified surface GAT prism measured IOP on 243 unique eyes. The study design and methodology complied with International Standard Organization (ISO) tonometer evaluation guidelines, except the inclusion of thin (<500 µm) and thick (>600 µm) corneas. All eyes were randomised to IOP measurement by one of five standard Goldmann prisms and five modified prisms. Pressures were measured by six investigators, two times with each prism for a total of 1936 IOP measurements. Analysis included a multiple linear regression including CCT and CH correlation.

Results: The difference in IOP measurements of the standard and modified Goldmann prisms correlated well to CCT particularly in thin (<500 µm) and thick (>600 µm) corneas (R2=0.404, p=0.007). Corneal hysteresis (CH) also significantly correlated to the difference in prism measurements (R2=0.125, p=0.039). There was no significant overall mean IOP bias between the two prisms (+0.43 mm Hg in modified, p=0.19).

Discussion: The paired IOP measurement difference between GAT and a modified surface Goldmann replacement prism indicated a statistically significant correlation to CCT and CH. A simple modified replacement prism for any Goldmann-type tonometer may significantly improve IOP measurement accuracy by minimising corneal biomechanical errors associated with CCT and CH.

Trial registration number: NCT02990169 and NCT02989909.

Keywords: Cornea; Glaucoma; Intraocular pressure; central corneal thickness; corneal biomechanics; corneal hysteresis; tonometry.

Conflict of interest statement

Competing interests: The submitted manuscript was completed by referencing studies funded by an NIH/NEI SBIR grant, 1R43 EY026821-01. Requirements of this grant are commercialisation of potentially beneficial ophthalmic/optometric medical devices/products. The commercialisation necessitates intellectual property and a company to produce the product. Commonly in new technology start-up companies, the corresponding author is also part owner in the intellectual property and the associated company (Intuor Technologies) producing the medical device. This is a conflict of interest. However, the authors attest to the stringent efforts made to provide unbiased information provided in this manuscript. We believe, as does the NIH and ASCRS, that the tonometer device has a potential to bring considerable value to the ophthalmic medical community and their patients.

© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

Figures

Figure 1

Applanating surface of the centrally concave and annularly convex (CATS) prism.

Figure 2

Scatter plot of the average intraocular pressure (IOP) values for GAT and modified (CATS) prisms from each of the 243 measurements along with a reference x=y line.

Figure 3

Measured intraocular pressure (IOP) difference between modified (CATS) minus GAT correlated to central corneal thickness, 95% CI on average mean difference and slope indicated by dashed lines.

Figure 4

Paired differences (CATS–GAT) between thin (600 µm) cornea groups compared using a two-sample Student’s t-test on the means. CCT, central corneal thickness; IOP, intraocular pressure.

Figure 5

Measured intraocular pressure (IOP) difference between modified (CATS) minus GAT correlated to corneal hysteresis, 95% CI on average mean difference and slope indicated by dashed lines.