Intraocular Pressure Values Obtained by Ocular Response Analyzer, Dynamic Contour Tonometry, and Goldmann Tonometry in Keratokonic Corneas

Purpose: To determine the agreement between dynamic contour tonometer (DCT), Goldmann applanation tonometer (GAT), and Ocular Response Analyzer (ORA) in keratoconic corneas and to find out the effect of corneal biomechanics on intraocular pressure (IOP) measurements obtained by these devices. Subjects and Methods: IOP was measured with the ORA, DCT, and GAT in random order in 120 eyes of 61 keratoconus patients. Central corneal thickness (CCT) and keratometry were measured after all IOP determinations had been made. The mean IOP measurement by the ORA and DCT was compared with the measurement by the GAT, using Student t test. Bland-Altman analysis was performed to assess the clinical agreement between these methods. The effect of corneal hysteresis (CH), corneal resistance factor (CRF), and CCT on measured IOP was explored by multiple backward stepwise linear regression analysis. Results: The mean +/- SD patient age was 30.6 +/- 11.2 years. The mean +/- SD IOP measurement obtained with GAT, ORA Goldmann-correlated IOP (IOPg), ORA corneal-compensated IOP (IOPcc), and DCT was 10.96 +/- 2.8, 10.23 +/- 3.5, 14.65 +/- 2.8, and 15.42 +/- 2.7 mm Hg, respectively. The mean +/- SD CCT was 464.08 +/- 58.4 microns. The mean difference between IOPcc and GAT (P<0.0001), IOPcc and DCT (P<0.001), GAT and DCT (P<0.0001), IOPg and GAT (P<0.002), and IOPg and DCT (P<0.0001), was highly statistically significant. In multivariable regression analysis, DCT IOP and GAT IOP measurements were significantly associated with CH and CRF (P<0.0001 for both). Conclusions: DCT seemed to be affected by CH and CRF, and the IOP values tended to be higher when compared with GAT. ORA-measured IOPcc was found to be independent of CCT and suitable in comparison to the DCT in keratoconic eyes.