The dynamic contour tonometer (DCT, Pascal tonometer, Swiss Microtechnology AG, Port, Switzerland) was recently introduced as a new method of intraocular pressure measurement, supposedly independent of corneal properties. In this study we analyzed the agreement and correlation of dynamic contour tonometry and Goldmann applanation tonometry (GAT) and investigated the influence of central corneal thickness (CCT) and corneal curvature. We also considered preferential patient groups for both methods.
In a prospective study of 100 eyes without glaucoma, intraocular pressure was measured using dynamic contour tonometry and Goldmann applanation tonometry, followed by measurements of central corneal thickness and corneal curvature.
A clear correlation between dynamic contour tonometry and Goldmann applanation tonometry was found (r = 0.693; P < 0.001). Dynamic contour tonometry generally resulted in higher intraocular pressure measurements (median difference + 1.8 mm Hg, mean difference + 2.34 mm Hg). Unlike dynamic contour tonometry, Goldmann applanation tonometry was remarkably affected by central corneal thickness, but neither method was significantly influenced by corneal curvature. Bland-Altman graphs showed remarkable disagreement between dynamic contour tonometry and Goldmann applanation tonometry, which could be partially explained by the influence of central corneal thickness on Goldmann applanation tonometry. To obtain valid readings, dynamic contour tonometry required a more extensive selection of patients than Goldmann applanation tonometry.
Dynamic contour tonometry seems to be a reliable method for intraocular pressure measurement, which unlike Goldmann applanation tonometry is not influenced by central corneal thickness. In clinical practice, advantages from dynamic contour tonometry can be expected for cooperative patients, outpatients, and patients with sufficient bilateral ocular fixation, whereas Goldmann applanation tonometry measurements are more reliable in case of patients with inadequate cooperation, poor vision, or nystagmus.