The Relationship between Corvis ST Tonometry and Ocular Response Analyzer Measurements in Eyes with Glaucoma

Abstract

It is important to compare the results of Corneal Visualization Scheimpflug Technology instrument (CST) measurements and Reichert Ocular Response Analyzer (ORA) parameters. The purpose of the study was to investigate the association between CST measurements and ORA parameters in ninety-five patients with primary open-angle glaucoma. Measurements of CST, ORA, axial length (AL), average corneal curvature (CC), central corneal thickness (CCT) and intraocular pressure (IOP) with Goldmann applanation tonometry (GAT) were carried out. The association between CST and ORA parameters was assessed using linear regression analysis, with model selection based on the second order bias corrected Akaike Information Criterion index. Measurements from ORA (corneal hysteresis [CH] and corneal response factor [CRF]) had high intraclass correlation coefficients (ICC) and low coefficients of variation, but some CST parameters showed much lower reproducibility, namely: A1 length, A2 length, highest concavity time and peak distance. Of 12 CST parameters tested, 8 were significantly correlated with CH and 10 were significantly correlated with CRF, however, the magnitude of the correlation coefficients were weak to moderate at best. The optimal model to explain CH using CST measurements was given by: CH = -76.3 + 4.6*A1 time + 1.9*A2 time + 3.1 * highest concavity deformation amplitude + 0.016*CCT (R2 = 0.67, p <0.001). Similarly, the optimal model for CRF was given by: CRF = -53.5 + 4.2*A1 time + 1.9*A1 length + 20.8*A1 deformation amplitude + 0.8*A2 time + 0.017*CCT (R2 = 0.73, p <0.001). ORA parameters show higher reproducibility than CST measurements. Although many CST parameters are significantly related to ORA parameters, the strengths of these relationships are weak to moderate.

A comparison of the corneal biomechanics in pseudoexfoliation glaucoma, primary open-angle glaucoma and healthy controls using Corvis ST

“…Other Corvis ST parameters showed a weak correlation with CH compared to the Corneal Resistance Factor (CRF). Additionally, Corvis ST parameters and CRF were significantly correlated with IOP (measured on Goldmann Applanation tonometry) but CH was not [ 29 ]. Therefore, although both devices measure the corneal response to an air puff, there are inherent differences between the devices which need to be recognized for a more appropriate interpretation of their measurements.…”

Corneal biomechanical properties are associated with the activity and prognosis of Angioid Streaks

“…This result also supported our finding that an AS eye with a rigid cornea required more frequent intravitreal anti-VEGF injections (active AS). Both ORA and CST measure corneal biomechanical properties; however, they measured different aspects 12 , because of the different measurement mechanisms. ORA measures the difference of pressure values at first and second applanation, whereas CST measures corneal morphological changes following the application of an air pulse.…”

“…The details of the ORA measurement were described previously 12 . Briefly, the ORA records two applanation pressures, prior to and following an indentation of the cornea with the application of a rapid air jet.…”

“…As detailed elsewhere 15 , CST, a non-contact tonometer, monitors the corneal response to an air puff pulse with a high-speed Scheimpflug camera, capturing 4,330 frames per second (Fig. 1 ) 12 . Corneal biomechanical characteristics are assessed by analyzing these images, and five main screening parameters including Deformation amplitude (DA) ratio, Integrated radius (IR), Ambrosio relational thickness horizontal (ARTh), and stiffness parameter at first applanation (SP-A1); Corvis biomechanical index (CBI) is calculated and displayed on the Vincigurra screening report with the current software version 1.3r1538 16 .…”

Relationship Between the Shift of the Retinal Artery Associated With Myopia and Ocular Response Analyzer Waveform Parameters

“…The details of the ORA measurement were described previously 27. Briefly, the ORA records two applanation pressures, before and after an indentation of the cornea with the application of a rapid air jet.…”