Comparison of intraocular pressure measurements by the Ocular Response Analyzer and Goldmann applanation tonometer after penetrating keratoplasty in keratoconic patients

Purpose: To compare intraocular pressure (IOP) readings measured by the Ocular Response Analyzer (ORA) with those measured by the Goldmann applanation tonometer (GAT) in keratoconic eyes following penetrating keratoplasty (PKP) and evaluate the influence of anatomical and biomechanical properties of the grafts on the IOP measurements Methods: In this cross-sectional study conducted on 45 keratoconic eyes of 36 patients (24 men and 12 women) undergoing PKP, IOP using the GAT (IOP GAT) and corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-related IOP (IOPg), and cornea-compensated IOP (IOPcc) using the ORA and central graft thickness (CGT) were measured. Bland-Altman and mountain plots were used to evaluate agreement between the tonometers. The correlation of graft curvature and astigmatism; CGT; and corneal biomechanical properties with IOP readings was investigated using multivariate regression analysis. Results: The mean age of patients was 29.8±6.1 years and they were followed up for 91.2±35.4 months postoperatively. Mean CH, CRF, and CGT were 10.2±2.1 mmHg, 10.1±2.2 mmHg, and 567.5±38.8 μm, respectively. Mean IOP GAT, IOPg, and IOPcc were 12.2±2.4, 15.1±3.5, and 15.8±3.3 mmHg, respectively (P<0.001). The 95% limit of agreement between IOP GAT and IOPg ranged from -3.6 to 9.3 mmHg. CH and CRF, but not CGT or keratometric astigmatism were significantly associated with IOP GAT, IOPg, and IOPcc. Conclusion: Following PKP in keratoconus, graft biomechanics had more influence on IOP values than anatomical features. In comparison to the GAT, the ORA yielded higher IOP values.