Comparison of intraocular pressure adjusted by central corneal thickness or corneal biomechanical properties as measured in glaucomatous eyes using noncontact tonometers and the Goldmann applanation tonometer

PURPOSE To investigate the correlation coefficients between intraocular pressure (IOP) before and after adjusting for central corneal thickness (CCT) and corneal biomechanical properties. PATIENTS AND METHODS A total of 218 eyes of 218 patients with primary open-angle glaucoma (mean age =71.5 years; mean spherical equivalent =-0.51 D; mean deviation determined by Humphrey visual field analyzer =-3.22 dB) were included in this study. The tIOP and tIOPCCT, which were adjusted by the CCT (with tIOP meaning IOP not adjusted by CCT, as determined using the CT-1P; and tIOPCCT meaning IOP adjusted by CCT, as determined using the CT-1P), were determined using a noncontact tonometer. The IOPg and IOPCCT, which were adjusted by CCT, and IOPcc adjusted by corneal biomechanical properties were determined using a Reichert 7CR (with IOPg meaning IOP not adjusted by CCT or corneal biomechanical properties, as determined using the Reichert 7CR; IOPCCT meaning IOP adjusted by CCT, as determined using the Reichert 7CR; and IOPcc meaning IOP adjusted by corneal biomechanical properties, as determined using the Reichert 7CR). The GT and GTCCT adjusted by CCT were determined using a Goldmann applanation tonometer (with GT meaning IOP not adjusted by CCT, as determined using the Goldmann applanation tonometer; and with GTCCT meaning IOP adjusted by CCT, as determined using the GAT). Pearson's correlation coefficients among the IOPs were calculated and compared. P-values <0.05 were considered as statistically significant. RESULTS The tIOP, tIOPCCT, IOPg, IOPCCT, IOPcc, GT, and GTCCT were 14.8±2.5, 15.0±2.4, 13.1±3.2, 13.3±3.1, 13.7±2.9, 13.2±2.4, and 13.4±2.3 mmHg (mean ± standard deviation), respectively. The correlation coefficient between tIOPCCT and tIOP (r=0.979) was significantly higher than that between tIOPCCT and the other IOPs (r=0.668-0.852; P<0.001, respectively). The correlation coefficient between IOPCCT and IOPg (r=0.994) or IOPcc and IOPg (r=0.892) was significantly higher than that between IOPCCT or IOPcc and the other IOPs (r=0.669-0.740; P<0.001, respectively). The correlation coefficient between GTCCT and GT (r=0.989) was significantly higher than that between GTCCT and the other IOPs (r=0.669-0.740; P<0.001, respectively). CONCLUSION The IOP adjusted by CCT or corneal biomechanical properties depends on the measurement instrument itself, rather than the adjustment methods, for eyes of patients with primary open-angle glaucoma.