Improved keratoconus detection by ocular response analyzer testing after consideration of corneal thickness as a confounding factor.

PURPOSE: To compare corneal hysteresis (CH) and corneal resistance factor (CRF) between normal eyes and eyes with keratoconus correcting for the effect of central corneal thickness (CCT) and to estimate keratoconus detection sensitivity and specificity of these parameters.
METHODS: Observational case series of 102 normal eyes (control group) and 77 eyes with keratoconus (keratoconus group). Examination included corneal topography, tomography, and biomechanical testing with the Ocular Response Analyzer (Reichert Technologies). The confounding effect of CCT was controlled by stratification (20-μm CCT intervals) and linear transformation. Receiver operating characteristic curves were used to identify optimal CH and CRF cutoff points for keratoconus detection. Main outcome measures were CCT, CH, CRF, and diagnostic performance of CH and CRF.
RESULTS: Corneal hysteresis and CRF were positively correlated to CCT in both groups. In the control versus keratoconus group, CH was 9.79 ± 1.51 vs 8.49 ± 1.48 (P<.0001) and CRF was 9.55 ± 1.64 vs 7.24 ± 1.43 (P<.0001), respectively. Only CRF remained significantly lower in eyes with keratoconus after CCT stratification in 20-μm intervals, and keratoconus grade influenced CH and CRF. Transformed CH and CRF data confirmed these results. Sensitivity and specificity of CRF cutoff points ranged between 83% and 94% and 69% and 83%, respectively. True positive rate for CRF in eyes with keratoconus with normal topography was 84%.
CONCLUSIONS: Corneal resistance factor was better than CH for detecting keratoconic corneas once the effect of CCT on ORA measurements was considered, even for topographically unaffected fellow eyes of patients with keratoconus. The CCT-corrected CRF cutoff values and transformed indices may be of clinical use. Copyright 2012, SLACK Incorporated.