Repeatability of intraocular pressure and corneal biomechanical properties measurements by the ocular response analyser

Background: The Ocular Response Analyser (ORA, Reichert Ophthalmic Instruments) is a non-contact applanation tonometer, providing two measures of intraocular pressure (IOP) - IOPg which represents a Goldmann equivalent IOP measure and IOPcc, representing a measure of IOP independent of corneal effects. In addition, the device provides two measures believed to represent corneal biomechanical properties: corneal hysteresis (CH) and corneal resistance factor (CRF). The aim of this study was to assess the repeatability of these measurements. Patients and Methods: One randomly chosen eye from 49 healthy volunteers was measured four times consecutively with the ORA prior to Goldmann applanation tonometry (GAT). The repeatability coefficient (RC), the coefficient of variation (CV) and the intraclass correlation coefficient (ICC) were calculated as a measure of intrasession repeatability. Results: CH was the most variable and IOPg the most repeatable measure, with an RC of 2.61 and 1.97, respectively, and ICC of 0.86 and 0.92, respectively. CV ranged between 5.73% for IOPg and 12.38% for CH. ORA IOP measurements were higher than GAT (IOPcc=17.43 +/- 3.23; IOPg = 17.53 +/- 3.0; GAT = 15.75 +/- 2.77 mmHg). Conclusions: ORA measurements show good short-term repeatability in normal volunteers. Thus, this device appears to be applicable in clinical practice.