Relation between corneal thickness and intraocular pressure measurement by noncontact and applanation tonometry

PURPOSE: To assess whether there is a significant difference in intraocular pressure (IOP) measurements between noncontact and applanation methods and if so, whether the difference is correlated with corneal thickness. SETTING: Işik Eye Clinic, Ankara, Turkey. METHODS: This prospective study comprised 120 eyes of 60 randomly selected patients. Noncontact tonometry, applanation tonometry, and pachymetry were performed in each eye. The results were compared and an analysis was performed to determine whether there was a correlation between the differences in IOP measurements and corneal thickness in the entire group and in subgroups composed of the halves and quarters of the group. RESULTS: The mean IOP in the entire group was 20.38 mm Hg +/- 4.97 (SD) with the noncontact tonometer and 18.84 +/- 4.47 mm Hg with the Goldmann applanation tonometer. The difference between the measurements with the noncontact method and those with the applanation method was statistically significant (P <.01) except in cases having a corneal thickness between 513 microm and 539 microm (P >.01). There was a positive correlation between corneal thickness and the difference in measurements by noncontact and applanation tonometry, and the magnitude of correlation was greater in cases with thicker corneas. CONCLUSION: The reliability of tonometers decreased with increasing corneal thickness, in which case higher readings were found, especially with the noncontact tonometer.