Sensitivity and specificity of novel biomechanical waveform parameters in detecting forme fruste keratoconus and keratoconus

Purpose: To evaluate the sensitivity and specificity of Ocular Response Analyser (ORA) indices: Keratoconus Match Index (KMI) and Keratoconus Match Probability (KMP) in distinguishing forme fruste keratoconus (FFKC) and keratoconus (KC) from normal eyes. Methods: A prospective observational study of 52 normal, 12 FFKC and 110 KC eyes that underwent scheimpflug topography (Oculus Pentacam) and ORA biomechanical assessment. Main outcome measures were Pentacam topometric indices and ORA corneal hysteresis (CH), corneal resistance factor (CRF), KMI and KMP. Correlations were analysed between KMI, topographic keratoconus classification (TKC) and topometric indices. Predictive accuracy of KMI was assessed by the Area under curve (AUC) of receiver operating curves (ROC). Results: Mean KMI was 1.25 ± 0.30 for normal, 0.76 ± 0.59 for FFKC and 0.32 ± 0.53 for KC eyes (p < 0.0001). Significant negative correlations were noted between KMI and TKC (r = −0.742, p < 0.0001) and topometric indices. KMI had higher sensitivity and specificity than CH and CRF in detecting KC (AUC: KMI = 0.929, CH = 0.806, CRF = 0.862) (p < 0.05) and FFKC (AUC: KMI = 0.771, CH = 0.641, CRF = 0.707 (p > 0.05). KMP identified 90.1% of normal eyes, 43.2% of FFKC eyes and 22. 09% of KC eyes as normal. Conclusions: Mean KMI values differ significantly between normal, FFKC and KC eyes. KMI appears to be a reliable indicator of KC diagnosis and severity as compared to CH and CRF values. KMP identifies a significant percent of KC eyes as normal and does not agree well with topographic KC diagnosis.