Effect of Corneal Thickness on Dynamic Contour, Rebound, and Goldmann Tonometry
Received 2 October 2005; accepted 19 June 2006. published online 21 September 2006.
Purpose
To identify correlations among intraocular pressure (IOP) measurements obtained using the rebound tonometer (RBT), the dynamic contour tonometer (DCT), and the Goldmann applanation tonometer (GAT). The effects of corneal thickness on the measures obtained using each of the 3 tonometers also were examined.
Design
Cross-sectional study.
Participants
One hundred forty-six eyes of 90 patients with ocular hypertension or glaucoma.
Methods
Intraocular pressure measurements were obtained in all patients using RBT, DCT, and GAT. Central corneal thickness was determined by ultrasound pachymetry. Patients were divided randomly into 6 groups to vary the order in which the tonometers were used. All IOP measurements were made by the same examiner, who was masked to the readings obtained.
Main Outcome Measures
Intraocular pressure and central corneal thickness.
Results
There was good correlation between IOP readings obtained using the RBT and GAT (r = 0.864; P<0.0001), between DCT and GAT (r = 0.871; P<0.0001), and between RBT and DCT (r = 0.804; P<0.0001). Rebound tonometer and DCT readings consistently were higher than GAT measurements (RBT-GAT median difference, 1.4±2.7 mmHg; DCT-GAT median difference, 4.4±2.6 mmHg). A Bland–Altman plot indicated that the 95% limits of agreement between RBT and GAT were −4.3 to 6.4 mmHg (slope = 0.056; P = 0.218), those between DCT and GAT were −0.7 to 9.5 mmHg (slope = 0.016; P = 0.717), and those between RBT and DCT were −3.1 to 9.8 mmHg (slope = −0.041; P = 0.457). Using RBT, the point that best discriminated between patients with an IOP 21 mmHg or less and more than 21 mmHg as determined by GAT was >23.3 mmHg (sensitivity, 66.7%; specificity, 92.1%); using DCT, this point was >22.7 mmHg (sensitivity, 95.6%; specificity, 71.3%). In terms of pachymetry, GAT and RBT behaved similarly. Using these instruments, differences of approximately 3 mmHg were detected between the groups of patients with the thinnest (<531 μm) and thickest (>565 μm) corneas, whereas a significantly lower difference (0.5 mmHg) was noted for the DCT.
Conclusions
Measurements obtained both with the RBT and DCT show excellent correlation with those provided by applanation tonometry. Both tonometers tend to overestimate the IOP measured with the GAT, particularly the DCT. This last tonometer seems to be less affected by the corneal thickness.
Hospital Clínico San Carlos and Instituto de Investigaciones Oftalmológicas Ramon Castroviejo, Universidad Complutense, Madrid, Spain.
Correspondence to Jose M. Martinez-de-la-Casa, MD, PhD, Martin Lagos sn, 28040 Madrid, Spain.
Manuscript no. 2005-892.
Supported in part by the Instituto de Salud Carlos III, Madrid, Spain (Proyecto C03/13: “Investigación Clínica y Básica para la Prevención de la Ceguera”).
No author has a financial interest in any product mentioned in the article.
ABSTRACT