Purpose: To compare intraocular pressure (IOP) values measured by both Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) in both normal and glaucomatous eyes, and to determine the relationship between these parameters and central corneal thickness (CCT).
Patients and methods: Forty-seven subjects with primary open-angle glaucoma and 38 normal subjects attended a 12-hour session during which IOP was assessed at 7 time points, every 2 hours, by both GAT and DCT. CCT was also assessed at the same visit. Mean IOP was calculated for each eye of each subject by each method from the 7 diurnal IOP measurements obtained.
Results: Mean IOP was higher when measured by DCT than by GAT in both normal (by 1.1 mm Hg, P<0.0001) and glaucomatous (by 1.6 mm Hg, P<0.0001) eyes. IOP measurements by GAT and DCT were moderately correlated in both normal (r(2)=0.354, P<0.0001) and glaucomatous (r(2)=0.552, P<0.0001) eyes. In normal eyes, there was a weak positive correlation between GAT IOP and CCT (r(2)=0.088, slope=0.022 mm Hg/microm, P=0.009) and no correlation between DCT IOP and CCT (r(2)=0.007, slope=0.005 mm Hg/microm, P=0.468). In glaucomatous eyes, there was no correlation between GAT IOP and CCT (r(2)=0.006, slope=0.007 mm Hg/microm, P=0.473) and a weak inverse correlation between DCT IOP and CCT (r(2)=0.075, slope=-0.021 mm Hg/microm, P=0.008).
Conclusions: Both GAT and DCT are affected by CCT, albeit in different ways. Normal and glaucomatous eyes exhibit different relationships between CCT and IOP measured by either GAT or DCT. The relationships between CCT and transcorneal IOP measurements are complex and incompletely characterized, which limits the clinical interpretation of GAT and DCT measurements of IOP in both normal and glaucomatous eyes.