Effect of central corneal thickness and corneal hysteresis on tonometry as measured by dynamic contour tonometry, ocular response analyzer, and Goldmann tonometry in glaucomatous eyes.

PURPOSE: The dynamic contour tonometer (DCT; Pascal tonometer) and the Ocular Response Analyzer (ORA) are novel tonometers designed to measure intraocular pressure (IOP) independent of corneal properties and central corneal thickness (CCT), respectively. We wanted to compare the corneal compensated IOP (IOPcc) as measured by ORA with IOP values measured by DCT and Goldmann applanation tonometry (GAT) with respect to IOP readings and the influence of corneal hysteresis (CH) and CCT in glaucoma patients. PATIENTS AND METHODS: In a study of 94 glaucomatous eyes, IOP measurements by ORA, DCT, and GAT were compared, and the effects of CCT and CH were analyzed. All measurements were taken by 1 of the authors only.
RESULTS: The Mean CCT was 550+/-44 mum and mean CH 10.24+/-3.3 mm Hg. The mean value for IOPcc was 17.94+/-5.9 mm Hg, 15.14+/-3.7 mm Hg for DCT, and 14.3+/-4.3 mm Hg for GAT. The mean difference was 3.65+/-3.85 mm Hg between IOPcc and GAT and 2.80+/-4.9 mm Hg between IOPcc and DCT (P<0.001) and -0.85+/-3.3 mm Hg between GAT and DCT (P=0.015). None of the methods was related to CCT. In contrast, CH was highly statistically significant related to IOPcc (P<0.0001), whereas GAT and DCT showed only weak relation to CH (P=0.05).
CONCLUSIONS: IOP measurements with the ORA are significantly higher than DCT or GAT with no apparent linear correction factor. To date, we cannot estimate the impact of differences in CH in relation to IOP and its measurement.