Correlation Between Dynamic Contour Tonometry, Uncorrected and Corrected Goldmann Applanation Tonometry, and Stage of Glaucoma

Abstract

Importance: Accurate determination of intraocular pressure (IOP) is crucial for the diagnosis and management of glaucoma. Objective clinical evaluation of the correction equations for Goldmann applanation tonometry (GAT) is lacking.

Objectives: To investigate the difference between corrected and conventional GAT and Pascal dynamic contour tonometry (DCT) measurements, as well as the correlation between discordant IOP values and stage of glaucoma.

Design, setting, and participants: This prospective cross-sectional case series was conducted at the Department of Ophthalmology, University Hospital Zurich, and Talacker Eye Center between July 1, 2011, and May 31, 2016, among 112 white patients with glaucoma.

Interventions: Intraocular pressure measurements were performed with GAT and DCT in a randomized order. Goldmann applanation tonometry measurements were modified with 5 correction equations.

Main outcomes and measures: The primary end point was degree of concordance between corrected or uncorrected GAT and DCT measurements. The secondary end point was association between discordant IOP measurements and the stage of glaucoma, as assessed by the Glaucoma Severity Score.

Results: Among the 112 patients (67 women and 45 men; mean [SD] age, 66.3 [13.1] years), 63 of the eyes in the study (56.3%) were left eyes and 85 patients (75.9%) were taking ocular antihypertensive medications. Mean (SD) IOP was 20.3 (4.5) mm Hg (95% CI, 19.4-21.1) as measured by DCT and 17.0 [4.1] mm Hg (95% CI, 16.3-17.8) as measured by GAT. The mean (SD) discordance between DCT and GAT measurements was -3.3 (2.0) mm Hg (95% CI, 2.9-3.6). The 5 corrected GAT values ranged from -2.7 to -5.4 mm Hg compared with DCT. The mean (SD) result of the Dresdner correction formula (17.6 [4.1] mm Hg) was closer to the DCT measurement than the original GAT measurement. The mean (SD) Glaucoma Severity Score was 4.7 (3.4) (95% CI, 4.1-5.4). The uncorrected discordance IOPDCT - IOPGAT showed a positive correlation with the Glaucoma Severity Score (rs = 0.33; P < .001) and a negative correlation with central corneal thickness (rs = -0.22; P = .02).

Conclusions and relevance: In comparison with DCT measurements, these data suggest that GAT values are significantly discordant in eyes with thin corneas and advanced glaucoma. Application of GAT-based correction formulas involves a possible risk of creating an even greater number of unpredictable measurement errors. Hence, we advise with caution, especially pertaining to eyes with thin corneas, to not place reliance on GAT readings, and abandon any correction formula.

Trial registration: clinicaltrials.gov Identifier: NCT01474070.

Figure 1.. Agreement Between Dynamic Contour Tonometry (DCT) and Goldmann Applanation Tonometry (GAT) Readings and Discordances From Intraocular Pressure (IOP) Measured by DCT

A, Bland-Altman plot illustrating the agreement between DCT and GAT readings. The discordance of both readings is plotted against their mean. Circles indicate the cases. Solid line indicates mean discordance and broken lines indicate 95% limits of agreement. B, Discordances from IOP measured by DCT for all correction formulas and uncorrected GAT. Shaded bars extend from lower to upper quartile. Horizontal lines in shaded bars indicate the median. Vertical lines extend from minimum to maximum value, excluding outliers. Circles indicate the outliers. The dotted horizontal line at zero indicates concordance.

Figure 2.. Association Between the Glaucoma Severity Score (GSS) and the Discordance of Dynamic Contour Tonometry (DCT) and Goldmann Applanation Tonometry (GAT) and the Central Corneal Thickness (CCT)

A, Association between the GSS and the discordance of DCT and GAT. Patients with discordant intraocular pressure readings tend to have a higher GSS. R₀ linear = 0.162. Circles indicate cases. The diagonal line is the regression line. B, Association between CCT and the GSS. Patients with thinner corneas tend to have more progressed glaucoma. Circles indicate cases. The diagonal line is the regression line. The dotted horizontal line at zero indicates concordance.