Research of diagnostic value of corneal biomechanical parameters based on Corvis ST in keratoconus

Objective

To compare the corneal biomechanical properties between keratoconic eyes and normal eyes by using corneal visualization Scheimpflug technology (Corvis ST), and to evaluate the diagnostic value of corneal biomechanical parameters based on Corvis ST in keratoconus.

Methods

A prospective cases-control study was performed.Twenty-four keratoconic eyes from 17 patients and 40 normal eyes (right eye) from 40 participants were enrolled from October to December in Peking University First Hospital.Anterior segment parameters and refractive diopters were obtained with Topography (TMS-4) and mydriatic refraction.Biomechanical parameters were assessed with Corvis ST.Independent sample t-test and Wilcoxon rank sum test were used to compare the parameters of the two groups.The receiver operating characteristic (ROC) curves were plotted to distinguish keratoconus from the normal cornea.Diagnostic efficacies of all parameters were analyzed and some parameters were used as independent variables to establish a Logistic regression model.

Results

Maximum deformation amplitude of highest concavity (HCDA), maximum corneal velocity during the second applanation (Vout) and distance between both non-deformed peaks (PD) in the keratoconus group were higher than those in the normal control group, and first applanation time (A1T), cord length of first applanation (A1L), cord length of second applanation (A2L), radius value of central concave curvature at highest concavity (HCR) were lower than those in the normal control group, with significant differences between the two groups (all at P<0.05). Maximum corneal velocity during the first applanation (Vin), second applanation time (A2T) and time taken to reach highest concavity (HCT) were insignificantly different between the two groups (all at P>0.05). Many parameters had diagnostic values in keratoconus assessed by ROC analysis.HCR was the most efficient parameter showed by ROC evaluation (area under the curve was 0.927, sensitivity was 95.8%, specificity was 82.5%). The Logistic model were established with two independent variables, HCR (OR=0.205) and central corneal thickness (CCT) (OR=0.970). The forecast model of keratoconus diagnosis was established as follows: Logistic (P)=23.47-1.59×HCR-0.30×CCT.Diagnostic sensitivity and specificity were enhanced by using this model, the sensitivity was 95.8%, and the specificity was 95.0%.

Conclusions

It is useful to evaluate the corneal biomechanical properties with Corvis ST.HCR is an efficient auxiliary testing index of diagnosis or screening of keratoconus.