The influence of corneal thickness and curvature on IOP measurement by IcareTM rebound tonometer and applanation tonometry in glaucoma patients and normal subjects.

Abstract Purpose To evaluate the influence of central corneal thickness (CCT) and radius of the corneal curvature (R) on IOP measurements obtained with the ICare rebound tonometer and the Goldmann applanation tonometer (GAT). Methods Eighty four eyes of 48 subjects (65 eyes of glaucoma patients and 19 eyes of healthy volunteers) were examined with ICare and Goldmann tonometers. Central corneal thickness was determined by ultrasound pachymetry. Corneal radius of curvature was determined using corneal topography. Results There was no significant difference between IOP readings with ICare and GAT. Intraocular pressure measurements were found to be higher with the ICare tonometer, both in glaucoma patients (15,3±4,0 mmHg) and normal subjects (14,4±3,0 mmHg). ICare‐GAT mean difference was 1.1±3.6mmHg (95% CI, ‐6.1‐8.3mmHg) for glaucoma patients and 1.8±3.2mmHg (95% CI, ‐4.6‐8.2mmHg) for healthy volunteers. Using CCT patients were divided into 2 groups: 1) thinnest corneas ‐ CCT<556 μm (mean CCT 531±23 μm), 39 eyes and 2) thickest corneas ‐ CCT >556 μm (mean CCT 578±17 μm), 45 eyes. In the group of thinnest corneas there was no correlation between IOP, CCT and R. In thickest corneas there was significant correlation between IOP readings obtained by ICare and CCT (r=‐0.4, p<0.01), and mean radius (R) (r=0.5, p<0.001). Conclusion Measurements of IOP using the ICare rebound tonometer are in good agreement with Goldmann applanation tonometer in glaucoma patients and normal subjects, although influenced by CCT.