Influence of Crosslinking on Astigmatism Vector in Keratoconus: A Vector Analysis

Introduction: Corneal cross linking (CXL) is an appropriate method to treat progressive keratoconus in order to stop progression. Generally, the change in the maximum corneal power (Kmax), corneal thickness, and total astigmatism are assessed for progression analysis. The aim of this study is to answer the question of whether corneal astigmatism is suitable for quantifying keratoconus progression or demonstrating stability. To improve accuracy, we analyze astigmatism as a vector parameter in CXL follow-up. Methods: We performed a retrospective observational study analyzing a total of 74 eyes diagnosed with progressive keratoconus that received CXL treatment and had a follow-up period of at least 12 months, and in some cases, up to 5 years. In the Scheimpflug imaging examination (Pentacam (R)), the focus was on the change of Kmax in diopter (D), astigmatism of the corneal front, and its vector parameter. Results: Preoperatively, we observed an increase in Kmax difference (KmaxD) (median +1.9 D +/- standard deviation, SD 2.2) and astigmatism vector difference (AVD) (median +0.7 D +/- SD 1.6) with a positive correlation, which establishes a treatment indication. The follow-up showed a stabilization of KmaxD and AVD after 12 months (median KmaxD -0.7 D, AVD -0.4), and over the periods of 3 and 5 years, a further stabilization of the curvature parameters with a lower number of cases. Conclusions: Compared with an analysis of an absolute value only, the vector analysis of astigmatism allows a much more precise description of astigmatism in order to verify the effectiveness of CXL. Both astigmatism vector and Kmax preoperatively increased and stabilized potstoperatively. Astigmatism presumably has a significant effect on the quality of vision and should therefore also be used as an additional stability factor beside Kmax.