Purpose: To compare intraocular pressure (IOP) measured by Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) and assess their relationship to central corneal thickness (CCT) in patients with primary open angle glaucoma (OAG).
Patients and methods: GAT, DCT, and CCT were assessed in 116 patients with OAG [mean age 65.9 (10.5); 59% female] participating in the Indianapolis Glaucoma Progression Study. GAT and DCT were measured in a randomized order followed by CCT (ultrasonic corneal pachymetry) during a single study visit. Bland-Altman plots were used to evaluate the limits of agreement between tonometery methodologies whereas multivariate regression analysis was used to evaluate the influence of CCT on GAT and DCT IOP measurements.
Results: IOP values obtained by DCT and GAT showed a strong positive correlation in patients with OAG (r=0.93; P<0.001). Mean IOP measured with DCT [18.4 (5.1) mm Hg] was significantly higher (P<0.001) than GAT IOP measurements [16.5 (4.5) mmHg]. CCT did not seem to influence either GAT or DCT measurements (r=0.1025, P=0.16; r=0.05, P=0.46), respectively. The Bland-Altman data showed that the amount of disagreement between IOP assessment techniques varied, suggesting a proportional bias.
Conclusions: In this group of patients with OAG, there was a strong correlation between GAT and DCT measurements of IOP. IOP measured with DCT was consistently higher than IOP measured with GAT. Neither GAT nor DCT measurements were correlated with CCT. This data suggests that factors other than CCT may be involved in the tendency of DCT to produce higher measures of IOP than GAT.