Posters

Topometric and tomographic parameters for the diagnosis of ectatic disease

Poster Details

First Author: R.Ambrosio Jr BRAZIL

Co Author(s):    I. Ramos   B. Lopes   M. Salomão   A. Luz   J. Lyra   M. Belin

Abstract Details

Purpose:

To investigate topometric (front surface curvature) and tomographic (3D elevation and thickness distribution) parameters for detecting ectatic corneal disease.

Setting:

Inst. Olhos R. Ambrósio; Rio de Janeiro Corneal Tomography and Biomechanics Study Group

Methods:

Topometric and tomographic indices were obtained using the Oculus Pentacam HR (Wetzlar, Germany) from 266 normals (N), from 282 keratoconus (KC) cases, and from 211 cases of forme fruste keratoconus (FFKC) were retrospectively reviewed. The eyes were classified accordingly to clinical data. The N group comprised from the preoperative state of cases that had LASIK with no ectasia development after one year. The KC group comprised from one eye randomly selected from patients with bilateral keratoconus. FFKC criteria was the eye with no clinical or topographic evidence of keratoconus, from patients with keratoconus diagnosed in the fellow eye. Diagnosis of keratoconus was based on the criteria from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. ANOVA with post-hoc t-tests or Kruskal - Wallis with post-hoc Dunn's test were used for assessing differences among the groups, accordingly to the distribution of the variables (Kolmogorov-Smirnov). The ability of the parameters to distinguish KC and FFKC from N was assessed by receiver operating characteristic (ROC) curve analysis.

Results:

All variables had significantly different distributions among the groups with area under the ROC curve (AUC) higher than 0.81 for N and KC. Only tomographic parameters had AUC higher than 0.81 for detecting FFKC from N. The best parameter was Ambrósio Relational Thickness (ART-Max) with AUC of 0.992 for detecting KC (95% CI: 0.980 to 0.997) and 0.877 for detecting FFKC (95% CI: 0.844 to 0.905). IHD (index of height decentration) was the best topometric parameter with AUC of 0.992 for detecting KC (95% CI: 0.970 to 0.994) and 0.781 for detecting FFKC (95% CI: 0.741 to 0.817). Belin/Ambrósio deviation (BAD-D, version 3), a combined parameter based on linear regression analysis, had AUC of 0.995 for detecting KC (95% CI: 0.982 to 0.998) and 0.892 for detecting FFKC (95% CI: 0.861 to 0.919). A new linear regression analysis including other parameters such as age and IHD based on the present database enabled the calculation of a new function, which enhanced the AUC to 0.998 for detecting KC (95% CI: 0.99 to 1.00) and 0.951 for detecting FFKC (95% CI: 0.923 to 0.97).

Conclusions:

Topometric and tomographic indices successfully detect keratoconus, but the integration parameters from curvature and 3-D analysis is necessary to enhance accuracy in identifying milder forms of ectasia. The integration of age, a surrogate of biomechanical properties of the cornea significantly improved the ability to identify ectatic diseases. FINANCIAL INTEREST: One of more of the authors... gains financially from product or procedure presented, One of more of the authors... receives consulting fees, retainer, or contract payments from a competing company