Comparison of waveform‐derived ORA parameters in clinical keratoconus, subclinical keratoconus and healthy subjects

Abstract

Aims/Purpose: The aim of this study was to comparison of waveform‐derived Ocular Response Analyser (ORA) parameters in clinical keratoconus (KC), subclinical keratoconus (SKC) and healthy subjects.Methods: This retrospective comparative case series study included 24 eyes with SKC, 24 eyes with KC and 48 eyes of age‐ and sex‐matched healthy subjects. Keratoconus diagnosis was based on clinical examinations, and Scheimpflug corneal tomography. SKC was defined as the presence of the following: (1) normal biomicroscopic findings and topography; (2) anterior (≤7 μm) and posterior (≤16 μm) elevation difference map marked green or yellow; (3) mean keratometry <47D; (4) BAD‐D value <3 SD and (5) keratoconus in the fellow eye. Thirty‐seven parameters derived from the waveform signal obtained with ORA were analysed. The Kruskal‐Wallis H test with Bonferroni correction was used for comparisons. p < 0.05 was considered statistically significant.Results: While the rate of females in all groups was 33.3%, the mean age was 25.6 ± 0.9, 25.8 ± 1.3 and 25.7 ± 0.8 years in KC, SKC and healthy subjects, respectively. Statistically significant differences between KC and healthy eyes were found in p1area (p = 0.005), p2area (p < 0.001), w1 (p = 0.001), w2 (p = 0.002), path1 (p = 0.032), path2 (p < 0.001), aplhf (p = 0.018), p1area1 (p = 0.021), p2area1 (p < 0.001), w11 (p = 0.028), w21 (p = 0.001), and path21 (p < 0.001). While there were significant differences in w2 (p = 0.016), w21 (p = 0.042), and path21 (p = 0.033) parameters between SKC and healthy eyes, no significant difference was found between SKC and KC eyes.Conclusions: Approximately one‐third of the waveform‐derived ORA parameters can be used to differentiate between KC and healthy subjects. Parameters derived from the second applanation signal of ORA were superior in distinguishing SKC from healthy subjects.