Ocular Response Analyzer (ORA) Waveform-Derived Biomechanical Parameters to Differentiate between Keratoconus and Healthy Thin Cornea

Aim: Evaluate the Ocular Response Analyzer ability in differentiating mild keratoconus from normal thin corneas CCT 500µm using each of the 41 parameters individually and to select the specific parameters that improve more ORA diagnosis of mild keratoconus. Study Design and Method: Prospective comparative case control study, in total 40 healthy eyes with CCT ≤500µm, and 40 eyes from CCT–, gender– and age-matched keratoconus cases were enrolled. Patients underwent a complete clinical eye examination, corneal tomography (Allegro Oculyzer, WaveLight AG, Erlangen, Germany) and biomechanical evaluations (ORA Reichert Ophthalmic Instruments, New York, USA). Comparison of numerical variables was done using independent samples t-test. The predictive ability of the ORA parameters was analyzed using ROC Curve. Results: The two groups were matched according to age, sex and CCT with CCT 491.35±8.4µm (range 471-500) in healthy thin corneas and 490.92±17.96µm (range 459-527) in keratoconus; (p=.863). Statistically significant differences between keratoconic and normal thin corneas were found in twenty six parameters (p 0.05). Fifteen parameters had moderate to good ability for keratoconus diagnosis with area under the ROC curve (AUROC) 0.7. Among the individual parameters, the parameters related to the height under the second peak (h2 and h21) had the best performance with AUROCs of 0.781. Conclusion: Waveform-derived ORA parameters displayed greater accuracy than pressure-derived parameters for identifying keratoconus.