Waveform Score Influences the Outcome Metrics of the Ocular Response Analyzer in Patients with Keratoconus and in Healthy Controls

Abstract

Purpose: To test whether the intraocular-pressure (IOP) and biomechanical outcome metrics from the Ocular Response Analyzer (ORA) differ between the measurement with the highest waveform score and the average of four measurements of any waveform score in participants with keratoconus and in controls.

Methods: Patients with diagnosed keratoconus and healthy controls were recruited prospectively. Four measurements were made using a third-generation ORA. Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), corneal resistance factor (CRF), waveform score, and six waveform parameters (p1area, p2area, w1, w2, h1, and h2) were considered as outcome metrics. In the left eye, outcomes from the measurement with the highest waveform score were compared against averaged outcomes from four measurements of any waveform score using either paired t-tests or Wilcoxon signed-rank tests. Receiver operating characteristic (ROC) curves tested ability of both data-selection approaches to differentiate the cohorts.

Results: One-hundred ninety-two (N = 192) participants were enrolled. In the control cohort (n = 145), waveform score, CH, p2area, and h2 were all significantly greater for the best-waveform-score measurement than for the average-waveform-score measurement. IOPcc and w2 were significantly less for the best-waveform-score measurement than for the average-waveform-score measurement. In the keratoconus cohort (n = 47), waveform score, p1area, p2area, h1, and h2 were all significantly greater for the best-waveform-score measurement than for the average-waveform-score measurement. W2 was significantly less for the best-waveform-score measurement than for the average-waveform-score measurement. The area under the ROC curve was high for both data-selection approaches.

Conclusion: In general, the best measurement had higher and narrower waveform peaks than the averaged measurement, which suggests better alignment between the device and the eye in the former than in the latter. Thus, making multiple measurements and then analyzing the one with the single highest quality may be preferred to analyzing the average of the group.

Keywords: cornea; corneal hysteresis; intraocular pressure; ocular biomechanics; waveform parameters.