Topometric and tomographic parameters for the diagnosis of keratoconus

Poster Details

First Author: F.Faria-Correia PORTUGAL

Co Author(s):    I. Ramos   B. Lopes   M. Salom   A. Luz   R. Correa   R. Ambr

Abstract Details

Purpose:

To investigate Pentacam topometric and tomographic parameters for discriminating keratoconic from normal corneas.

Setting:

Instituto de Olhos Renato Ambrósio; Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro, Brazil.

Methods:

One eye randomly selected from 200 patients with normal corneas (group N) and from 177 patients with keratoconus (group KC) were included Pentacam HR Oculus, Wetzlar, Germany) was performed in all cases. Topometric indices derived from curvature and asphericity, tomographic indices derived from front and back surface elevation,and tomographic indices derived from thickness were analyzed. The Mann–Whitney or Wilcoxon rank-sum test was used to test if each variable had different distributions among N and KC groups. The usefulness of these data to discriminate among the groups was assessed by receiver operating characteristic curve (ROC) analysis. The area under the ROC (AUROC) curve of each parameter was calculated, providing the best cut off value for optimizing sensitivity and specificity for the diagnosis of keratoconus. Pairwise comparisons of the AUROC ware performed using DeLong’s method.

Results:

All tested variables had significant differences among N and KC (p < 0.001). Topometric parameters ISV, IHD, IVA, KI, CKI , IHA and KMax had AUROC of 0.977, 0.973, 0.958, 0.978, 0.827, 0.890 and 0.972 respectively. The AUROC for K1, K2, astigmatism were 0.771, 0.901 and 0.852 respectively. ISV, IHD, KI had better AUROC than K1, K2 and astigmatism (p<0.001). The AUROC for thinnest and central thickness were 0.932 and 0.956 respectively. AUROC for average and maximal relative pachymetric progressions (RPI) were 0.996 and for ART-Avg and -Max (Ambrósio Relational Thickness Average and Maximal) were 0.999. ART and RPI were superior than single thickness (p<0.001). The AUROC for anterior elevation at the thinnest point, at the apex and the maximal elevation within 4mm were 0.973, 0.834, and 0.957 using 8mm best-fit-sphere (BFS) and 0.967, 0.856, 0.955 using 8mm best-fit-toric-ellipsoid (BFTE). The AUROC for posterior elevation at the thinnest point, at the apex and at the maximal elevation value were 0.983, 0.858, and 0.976 using 8mm BFS and 0.987, 0.856, 0.972 using 8mm BFTE. AUROC for the Belin-Ambrósio D index (3rd generation BAD-D) was 1.0. AUROC for BAD-D and for ART were superior than the best topometric and elevation indices (p<0.05).

Conclusions:

Topometric and tomographic indices were successful for detecting keratoconus. Tomographic indices derived from thickness distribution were superior to detect keratoconus than curvature based methods. The BAD-D combined parameter based on a regression analysis of the deviation of the elevation and thickenss tomographic parameters provide an enhanced approach for detecting keratoconus. These parameters should be tested and further optimized in milder forms of ectatic corneal diseases. FINANCIAL DISCLOSURE?: ... gains financially from product or procedure presented, ... receives nonNomonetary benefits from a company producing, developing or supplying the product or procedure presented.