Comparison of Different Topographic Reference Surfaces in Keratoconus Cases

Abstract

OBJECTİVE: To compare the sensitivity and specificity of elevation maps obtained from different topographical reference surfaces used in the diagnosis of keratoconus. MATERİALS AND METHODS: In this study 40 eyes of 23 patients with keratoconus and 40 eyes of 25 refractive surgery candidates as a control group was measured with a Scheimpflug camera (Sirius CSO-Italy). Using the receiver operator characteristic curves (ROC), a comparison was made of the ability to differentiate keratoconus from a normal cornea with anterior elevation(AE) and posterior elevation(PE) measurements obtained from the spherical, aspherical, asphero-toric reference surfaces. RESULTS: The ROC curve analysis showed that posterior elevation measured from the aspherical and asphero-toric surfaces had a significantly higher area under the ROC curves (0.987, 0.973 respectively) thanthevalueobtainedfromthesphericalreferencesurfaces. According to the data obtained from the ROC curve analysis, the posterior elevation maps obtained from the aspherical and asphero-toric reference surfaces had the highest sensitivity (97.5% for both) and the posterior elevation map obtained from the aspherical reference surface had the highest specificity (90%). CONCLUSION: The highest sensitivity and specificity values were obtained from the aspherical and asphero-toric reference surfaces rather than from the spherical reference surface. When compared to the anterior elevation values, the posterior elevation values were found to be more sensitive and specific. Therefore, aspherical and asphero-toric reference surfaces and a posterior elevation map would seem to be more accurate in the differentiation of keratoconus and normal cornea.

Keywords

• keratokonus
• kornea
• korneal topografi
• referans yüzey seçimi
• scheimpflug kamera
• scheimpflug camera
• cornea
• corneal topography
• keratoconus
• reference body selection