Aim To define variables for the evaluation of keratoconus progression and to determine cut-off values.
Methods In this retrospective cohort study (2010–2016), 265 eyes of 165 patients diagnosed with keratoconus underwent two Scheimpflug measurements (Pentacam) that took place 1 year apart ±3 months. Variables used for keratoconus detection were evaluated for progression and a correlation analysis was performed. By logistic regression analysis, a keratoconus progression index (KPI) was defined. Receiver-operating characteristic curve (ROC) analysis was performed and Youden Index calculated to determine cut-off values.
Results Variables used for keratoconus detection showed a weak correlation with each other (eg, correlation r=0.245 between RPImin and Kmax, p<0.001). Therefore, we used parameters that took several variables into consideration (eg, D-index, index of surface variance, index for height asymmetry, KPI). KPI was defined by logistic regression and consisted of a Pachymin coefficient of −0.78 (p=0.001), a maximum elevation of back surface coefficient of 0.27 and coefficient of corneal curvature at the zone 3 mm away from the thinnest point on the posterior corneal surface of −12.44 (both p<0.001). The two variables with the highest Youden Index in the ROC analysis were D-index and KPI: D-index had a cut-off of 0.4175 (70.6% sensitivity) and Youden Index of 0.606. Cut-off for KPI was −0.78196 (84.7% sensitivity) and a Youden Index of 0.747; both 90% specificity.
Conclusions Keratoconus progression should be defined by evaluating parameters that consider several corneal changes; we suggest D-index and KPI to detect progression.
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MS and GS contributed equally.
MS and GS are first authors.
Contributors MS contributed towards concept and design, data acquisition, data analysis/interpretation, drafting the manuscript, critical revision, statistical analysis and final approval. GS contributed towards concept and design, data acquisition, data analysis/interpretation, drafting the manuscript, critical revision, statistical analysis and final approval. KH contributed towards data acquisition, drafting the manuscript and final approval. KBK contributed towards data acquisition, data analysis/interpretation and final approval. IP contributed towards data acquisition, data analysis/interpretation and final approval. EP contributed towards data acquisition, drafting the manuscript and final approval. IS contributed towards concept and design, critical revision and final approval. TK contributed towards concept and design, critical revision and final approval.
Funding MS: consultant—Oculus, Oertli, Santen, Zeiss; GS: none; KH: none; KBK: none; IP: none; EP: none; IS: none; TK: research funding—Hoya, J&J Vision (Abbott), Novartis (Alcon), Oculentis, Oculus, Schwind, Zeiss; consultant or advisory board—Geuder, J&J Vision (Abbott), Novartis (Alcon), Oculus, Santen, Schwind, STAAR, TearLab, Thea Pharma, Thieme Compliance, Ziemer, Zeiss.
Competing interests None declared.
Patient consent Not required.
Ethics approval Ethik-Kommission des Fachbereichs Medizin der Goethe-Universität Frankfurt am Main.
Provenance and peer review Not commissioned; externally peer reviewed.
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