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

Abstract

PurposeClinically 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.DesignProspective, open-label, randomised, controlled, multicentre reference device accuracy analysis.MethodsA 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.ResultsThe 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).DiscussionThe 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 numberNCT02990169 and NCT02989909.

<p>Reliability of Intraocular Pressure Measurement by Goldmann Applanation Tonometry After Refractive Surgery: A Review of Different Correction Formulas</p>

“…In the attempt to find a reliable method in measuring the IOP after CRS, several devices have been tested, such as pneumotonometer, Tono Pen (TP), non-contact tonometer (NCT), such as TonoPachymeter, dynamic contour tonometer (DCT), Ocular Response Analyzer (ORA), Corvis ST and CATS Tonometer and only the last four has been proven to be as reliable as GAT. [42][43][44][45][46][47][48][49][50][51][52] Schipper, 26 to rehabilitate the GAT, in 2000 suggested to measure the IOP with GAT and TP in the corneal periphery because they found a higher IOP of 1.8-2.3 mmHg in the corneal periphery compared to the values measured in the central corneal region.…”

<p>Improved Efficacy of Topical Latanoprost 0.005% Demonstrated by Corneal Biomechanical Correcting Modified Goldmann Prism</p>

“…The 72 eye sample size was calculated using the difference between two paired means with an α=0.05 (2-tailed), β=0.2, power=0.85 and the mean differences and standard deviations from previous studies. 20,22,25 The following exclusionary conditions were prevented from study participation: corneal scarring, lid, corneal, or ocular conditions, disease, disorders, or infection that potentially affect corneal biomechanics and may have confounded the study results. Also excluded from the study were high myopes (>6 diopters) and high astigmatism (>3 diopters).…”

“…(Figure 1) Several studies, including intracameral pressure comparisons, have shown the CATS prism to have significantly decreased sensitivity to variations in corneal biomechanical properties when compared to the GAT prism. 22,[25][26][27][28][29] The design differences were described in detail previously. 22 Differences in IOP between the CATS and GAT measurements were strongly correlated with variations in corneal biomechanical properties such as CCT and CH.…”

“…22 Differences in IOP between the CATS and GAT measurements were strongly correlated with variations in corneal biomechanical properties such as CCT and CH. 22,25,[27][28][29] The CATS prism demonstrates a more accurate IOP as it negates much of the tonometer force due to corneal biomechanical deformation measuring predominantly the IOP when compared to the GAT prism. Furthermore, there was no overall IOP bias demonstrated between the two prisms over a large standard population.…”

“…22,[25][26][27][28][29] Since both prisms measure the same pressure for a cornea with nominal biomechanical properties, it is likely that the difference in CATS and GAT IOP is a direct measurement (in mm Hg) of those combined corneal biomechanical properties affecting its deformation. 25,26 The present study was completed to evaluate the effect of PGAs on IOP measurement accuracy and measure changes in corneal biomechanical properties. In addition, the study participants were equally randomized to timolol maleate treatment to delineate the effects of lowering IOP on the corneal biomechanics and IOP differences.…”