Goldmann Applanation Tonometry Versus Ocular Response Analyzer for Intraocular Pressure Measurements in Keratoconic Eyes

Abstract

To compare intraocular pressure (IOP) measurements obtained with the Goldmann applanation tonometer (GAT) and the ocular response analyzer (ORA) in patients with keratoconus (KC) and analyze their dependence on ocular anatomic parameters. Patients with KC were recruited prospectively. IOP was measured using GAT and ORA. The ORA provided a Goldmann correlated IOP (IOPg) and a corneal correlated IOP (IOPcc). Assessment of refractive status, visual acuity, axial length, corneal topography, and pachymetry was done. Fifty-nine eyes of 59 patients with KC (39 men, 20 women; mean age: 27.8 +/- 6.8 years) were included. The differences in mean IOP values between GAT (10.9 +/- 2.0 mm Hg) and IOPg (9.5 +/- 2.8 mm Hg) and between GAT and IOPcc (13.3 +/- 2.5 mm Hg) were statistically significant (all P < 0.001). Both pressure measurements provided by the ORA showed significant correlation with corneal curvature. No significant effect of corneal thickness on any of the pressures was observed. IOP measurements taken with GAT and ORA in keratoconic eyes were significantly different. Although IOPcc was significantly higher, IOPg was significantly lower than GAT IOP. Unlike GAT measurements, ORA readings seemed to be affected mainly by corneal curvature. As a result of described differences, we suggest these devices should not be used interchangeably but rather in a complementary fashion to assess IOP in keratoconic eyes.