Topometric indices in patients with corneal ectasia and healthy controls

Introduction: Keratoconus and marginal pelucid degeneration are bilateral, non-inflammatory diseases of the cornea, characterized by stromal thinning and progressive protrusion. They lead to a significant deterioration of the visual acuity due to irregular astigmatism. Sometimes these two conditions are hard to distinguish from one another. Aim: The aim of this article is to determine the diagnostic value of the topometric indices and their role in diagnosing corneal ectasia. Patients and Methods: Using corneal topography OCULUS Keratograph 5M, we examined 80 eyes of 43 patients with corneal ectasia and 86 eyes of 43 patients with no signs of corneal disease. We evaluated the topographic maps and the following indices generated by the device: Rv (vertical radius), Rh (horizontal radius), Kmax, ISV (index of surface variance), IVA (index of vertical asymmetry), KI (keratoconus index), CKI (center keratoconus index), RMin (minimal radius), IHA (index of height asymmetry), IHD (index of height decentration), ABR (aberration). The statistical analysis was performed by SPSS version 15 and the following test: Mann–Whitney U test and receiver operating characteristic (ROC) analysis. Results: Statistically significant difference was found for all the examined parameters p < 0.001 using 95% confidence interval. The ROC analysis determined area under the curve in the range from 0.992 for ABR and IHA to 0.927 for CKI. Conclusion: The topometric indices have excellent capabilities in differentiating ectatic from normal corneas.