Purpose: To evaluate the relationship between central corneal thickness and intraocular pressure (IOP) measured by iCare rebound tonometry (RBT) in normals and glaucomatous patients.
Methods: Of 102 patients screened, we included 62 eyes with glaucoma and 77 normal eyes in this hospital-based cross-sectional study. IOP was measured with RBT which averages 6 readings followed by Goldmann applanation tonometry (GAT). Central corneal thickness (CCT) was obtained by ultrasound pachymetry with an average of 5 consecutive readings. Relationship between RBT and CCT was studied by regression techniques using clustered data.
Results: A total of 62 eyes of 33 patients with known glaucoma and 77 eyes of 40 normal patients (male: female=72.6%:27.4%) with a mean age of 51±17.7 years were included. The mean CCT was 531±32.9 μm (range, 448 to 626 μm). The median deviation of iCare RBT from GAT was 1 mm Hg (range, -7 to 20 mm Hg), which was not statistically different between normals and glaucomatous patients. The difference in IOP obtained by the 2 measurements (RBT-GAT) was found to be significantly influenced by CCT in all eyes combined (β=0.04, P=0.01).and in glaucomatous eyes (β=0.06, P=0.01) increasing maximally by 1 mm Hg for every 10 μm increase in corneal thickness in those with glaucoma. Comparing the difference between eyes with different corneal thickness, the influence was seen maximally in glaucomatous eyes with cornea thicker than 531 μm, (β=2.3, P=0.03).
Conclusions: Difference of IOP obtained by RBT and GAT increases with increasing CCT. Consideration of this must be kept in mind while using rebound tonometer for IOP recording in glaucomatous patients.