Detection of Keratoconus With a New Biomechanical Index

Abstract

he early diagnosis of corneal ectasia is of foremost importance in both screening for refractive surgery and the early treatment of keratoconus. Topography or tomography analysis using either videokeratography or optical coherence tomography instruments can help detect alteration in the shape of the cornea such as thinning and increased curvature. However, these instruments cannot measure the mechanical stability, which is thought to be the initiating event of the disease, even before notable changes in corneal morphology take place.1,2 For this reason, there has been increasing interest in developing instruments to measure the in vivo biomechanical properties of the cornea to aid the diagnosis of an ectasia in a "biomechanical" stage, when topography and tomography are nor-T ABSTRACT PURPOSE: To evaluate the ability of a new combined biomechanical index called the Corvis Biomechanical Index (CBI) based on corneal thickness profile and deformation parameters to separate normal from keratoconic patients.METHODS: Six hundred fifty-eight patients (329 eyes in each database) were included in this multicenter retrospective study. Patients from two clinics located on different continents were selected to test the capability of the CBI to separate healthy and keratoconic eyes in more than one ethnic group using the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). Logistic regression was employed to determine, based on Database 1 as the development dataset, the optimal combination of parameters to accurately separate normal from keratoconic eyes. The CBI was subsequently independently validated on Database 2. RESULTS:The CBI included several dynamic corneal response parameters: deformation amplitude ratio at 1 and 2 mm, applanation 1 velocity, standard deviation of deformation amplitude at highest concavity, Ambrósio's Relational Thickness to the horizontal profile, and a novel stiffness parameter. The receiver operating characteristic curve analysis of the training database showed an area under the curve of 0.983. With a cut-off value of 0.5, 98.2% of the cases were correctly classified with 100% specificity and 94.1% sensitivity. In the validation dataset, the same cut-off point correctly classified 98.8% of the cases with 98.4% specificity and 100% sensitivity. CONCLUSIONS:The CBI was shown to be highly sensitive and specific to separate healthy from keratoconic eyes. The presence of an external validation dataset confirms this finding and suggests the possible use of the CBI in everyday clinical practice to aid in the diagnosis of keratoconus.[J Refract Surg. 2016;32(12):803-810.]

Comparison of corneal dynamic parameters and tomographic measurements using Scheimpflug imaging in keratoconus

“…It is derived from a combination of Corvis parameters including DA ratio, A1V, SD of HCDA, Ambrosio’s relational thickness to the horizontal profile and a stiffness parameter. It was found to have good discriminatory aptitude between normal and keratoconus eyes when tested on two independent populations 31. Apart from tomographic or mechanical parameters, optical quality assessment has been demonstrated to be useful in diagnosing and staging keratoconus 9 32.…”

Enhanced Screening for Ectasia Risk prior to Laser Vision Correction

“…4), 10,22,28 the Corvis ST Interestingly, the CBI (corneal biomechanical index) is a novel biomechanical index that was developed by Vinciguerra et al to integrate corneal deformation response metrics from the Corvis ST, having high accuracy to detect clinical ectasia. 37 Ultimately, the integration of biomechanical data and corneal shape data has been proposed for further improving accuracy to detect mild ectasia or even its susceptibility.…”

Effect of Age on Pentacam Keratoconus Indices

“…Early and accurate keratoconus (KC) detection using variable indices has been widely discussed, comparing the sensitivities and specificities of various parameters [3–5]. Furthermore, new algorithms and combined indices have been introduced, aiming at earlier and more precise KC detection [6, 7]. …”