Corneal Deformation Response with Dynamic Ultra-high-speed Scheimpflug Imaging for Detecting Ectatic Corneas

Abstract

Purpose:To test the ability of metrics derived from corneal response to noncontact tonometry (NCT) to distinguish between normal and ectatic cases. Materials and methods:The prototype of CorVis ST (Oculus, Wetzlar, Germany) was used for assessing corneal biomechanical response using ultra-high-speed 8 mm horizontal Scheimpflug photography, taking 4,330 frames per second during NCT. Patients were stratified based on clinical data, including rotating Scheimpflug corneal tomography (Oculus Pentacam HR). Biomechanical data from one eye randomly selected of 177 patients with normal corneas (N) and from 79 patients with bilateral keratoconus (KC) were investigated. Group forme fruste keratoconus (FFKC) was composed of 20 eyes with normal topographic patterns from cases with ectasia detected in the fellow eye. Group keratoconus suspect (KCS) had 16 eyes from 16 patients with topographic patterns suspicious of KC but documented stability over 3 years and normal tomographic findings. A combination of deformation parameters using linear regression analysis (Prototype Factor 1, pF1) was created by the BrAIn (Brazilian Artificial Intelligence on Corneal Tomography and Biomechanics) study group in order to provide the best possible separation of KC and normals.Results: Statistical significant differences were found for N × KC for several parameters, including first and second applanation times, deformation amplitude, and maximal concavity radius (Mann-Whitney, p < 0.001). However, the areas under the receiver operating characteristic curves (AUC) were lower than 0.90. The pF1 had AUC of 0.945 (IC 0.909-0.97; sensitivity = 87.3% and specificity = 89.3%). The pF1 had statistically significant differences between the ectatic (KC and FFKC) and nonectatic groups (N and KCS) (p < 0.05, Kruskall-Wallis Test with post hoc Dunn's test). Conclusion:Corneal deformation response analysis by ultrahigh-speed 8 mm horizontal Scheimpflug photography provides relevant data for distinguishing ectatic and nonectatic corneas but cannot be used independently to detect KC. This data may be integrated with corneal tomography data for enhancing sensitivity and specificity for screening ectasia.

Comparison of the morphological and biomechanical characteristics of keratoconus, forme fruste keratoconus, and normal corneas

“…Earlier studies on keratoconus biomechanics found that the differences in biomechanical parameters between the normal cornea group and keratoconus group were statistically significant, and the AUC of the parameters overlapped between 0.673 and 0.852. 10,26,27 With the introduction of new Corvis ST parameters, more related studies have appeared. Research by Vinciguerra et al 28 found that CBI has the highest efficiency in distinguishing keratoconus and normal corneas in biomechanical parameters, with a sensitivity and specificity of 100% and 98.4%, respectively.…”

Comparative analysis of the morphological and biomechanical properties of normal cornea and keratoconus at different stages

“…Previous biomechanical studies found that the maximum DA was the most effective parameter in diagnosing keratoconus, with an AUC of 0.882, but there was significant overlap between the keratoconus group and the control group [ 10 ]. Salomao et al found significant statistical differences in corneal biomechanical parameters between the normal cornea and keratoconus, but the AUCs of the parameters overlapped between 0.673 and 0.852 [ 29 ]. With the update of Corvis ST software, new biomechanical parameters have been proposed such as DA Ratio 2, Integrated Radius, ARTh, SPA1 and CBI.…”