Evaluation of Goldmann applanation tonometry, rebound tonometry and dynamic contour tonometry in keratoconus

PURPOSE: To compare the intraocular pressure (IOP) measurements obtained with the rebound tonometry (RT), dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in keratoconic corneas and to investigate the effects of central corneal thickness (CCT) and corneal radius of curvature (CR) on IOP measurements. METHODS: Sixty-three eyes of 63 keratoconus patients were enrolled in this cross-sectional study. IOP was measured on each subject always in the same order, ICare RT-Pascal DCT-GAT, after a minimum interval of 10 min between measurements. CCT and CR were measured using a rotating Scheimpflug camera before the IOP measurements in all subjects. One way repeated measures ANOVA and Pearson correlation coefficient analysis was used for the statistical assessment. RESULTS: Mean IOP for all enrolled eyes was 11.72 ± 2.59 mm Hg for GAT, 9.34 ± 3.29 mm Hg for RT, and 15.42 ± 3.31 mm Hg for DCT. There were statistically significant differences among the three tonometers; GAT and RT (P < 0.001), GAT and DCT (P < 0.001), and RT and DCT (P < 0.001). GAT and RT were significantly positively correlated with CCT (r = 0.288, P = 0.025 and r = 0.483, P < 0.001, respectively). RT was also significantly positively correlated with CR (r = 0.550, P < 0.001). DCT was not significantly correlated with CCT (r = 0.115, P = 0.377) nor CR (r = −0.179, P = 0.168). CONCLUSIONS: DCT has overestimated but RT has underestimated IOP readings according to GAT measurements in keratoconic corneas. DCT may be the most appropriate tonometer to use in keratoconus for the measurements of IOP, because DCT do not appear to be dependent upon CCT and CR.