Long-Term Zonal Average Analysis of Corneal Tomography in Keratoconus Eyes

Purpose: The scope of this study was to investigate keratoconus progression using zonal average analysis of corneal tomography. Methods: The corneal tomographies of patients participating in initial baseline and all scheduled follow-up visits up to 4 years were analyzed. Data were exported in custom software, which delineated 4 zones of analysis and calculated the average values of the anterior and posterior curvature and the average thickness for each zone at each visit. In particular, a 3.1 mm area containing the K, termed "keratoconus cone zone," was defined for assessing disease progression during the follow-up. Results: A total of 201 patients were enrolled in this prospective study. At 4 years, 31% of the eyes (n = 62) had an average increase of $1.0 D in the keratoconus cone zone in baseline visit, whereas only 11% of the eyes (n = 22) had $1.0 D K increase in the same period. The zonal anterior average curvature (+1.1 D; P, 0.001) and thickness (214 mm; P, 0.001) values of the keratoconus cone zone progressed significantly during the follow-up. A high correlation was found between the 4-year changes of K and central corneal thickness values and the change of the average anterior curvature and thickness values in the keratoconus cone zone. The posterior cornea did not show significant average changes (,20.2 D; P . 0.05) during the follow-up. Conclusions: Single-point tomography indexes for keratoconus progression did not capture the overall structure and shape changes of the cornea. It would be recommended to update criteria for keratoconus management including the zonal average analysis of curvature and thickness values for tracking disease progression over observation periods longer than 1 year.