The diagnostic value of ultra-high frequency Scheimpflug corneal biomechanical analysis in keratoconus patients

Abstract

Objective To evaluate the cut-off points and diagnostic value in keratoconus of the ultra-high frequency Scheimpflug corneal biomechanical analyzer. Methods In this descriptive study, the same operator, using the same biomechanical analyzer, measured the 12 parameters of 93 keratoconus eyes and 84 control eyes. From Eye Hospital of Wenzhou Medical University during December 2013 to July 2015. The subjects were staged with the Amsler-Krumeich keratoconus classification. Differences of parameters between the two groups were analyzed, and the cut-off points (COP) for the parameters between the groups was analyzed by receiver operating characteristic (ROC) curves. The area under the curve (AUC) method was used to evaluate the diagnostic value of the 12 parameters. Results Except for applanation 1 length (AP1 L), applanation 2 time (AP2 T), and maximum deformation amplitude (A), all other parameters were significantly different between the keratoconus and the control eyes (P 0.17 m/s, applanation 2 length (AP2 L) ≤1.49 mm, applanation 2 velocity (AP2 V) >0.42 m/s, peak distance (PD) ≥ 4.78 mm, A >1.24 mm, maximum deformation curvature (C) ≤5.66 mm, maximum deformation time (T) ≤16.40 ms, intraocular pressure (IOP) ≤13.50 mmHg, and central corneal thickness (CCT) ≤494 μm. Of all the parameters, C, AP1 V, and T had a medium level of diagnostic value. For these parameters, the AUC values were 0.738 (sensitivity 47.3%, specificity 94.0%), 0.751 (sensitivity 61.3%, specificity 88.1%), and 0.887 (sensitivity 77.4%, specificity 91.7%), respectively. The CCT and PD had good diagnostic values, with AUCs of 0.926 (sensitivity 82.4%, specificity 92.9%) and 0.930 (sensitivity 92.5%, specificity 85.7%), respectively. Conclusion Some of the CorVis-ST parameters have medium to good diagnostic value for keratoconus, while the CCT and PD have good diagnostic value. This suggests that the CorVis-ST could provide useful assistance in the clinical diagnosis of keratoconus. Key words: Keratoconus; Scheimpflug; Receiver operating characteristic curve; Cutting-off point