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The goal of laser refractive surgery is to achieve predictable and stable correction of myopia, hyperopia, and astigmatism. New, sophisticated diagnostic instruments such as topographers and aberrometers offer potential for improved results in terms of treatment efficiency and visual quality.( MaRae t al. 2000, Seiler et al. 2000, Manns et al. 2002, Mrochen et al. 2004) Many articles have been published concerning laser correction of myopia and hyperopia with and without astigmatism, but few dealing with mixed astigmatism (Chayet et al 1998, Chayet et al 2001, Hasabla et al. 2003, Albarran-Diego et al. 2004, De Ortueta&Haecker 2008, Stonecipher et al. 2010). In the late 90’s Chayet (Chayet et al 1998, Chayet et al 2001), and Vinciguerra (Vincinguerra et al. 1999) published toric ablation techniques, which apply a myopic cylinder and a hyperopic cylinder (90 degrees away). Azar (Azar&Primack 2000) and Gatinel (Gatinel et al. 2002) compared the theoretical ablation profiles and depths of tissue removal for all kinds of astigmatism using various ablation strategies such as combined hyperopic spherical and myopic cylindrical treatments, combined spherical (plus or minus) and hyperopic cylindrical treatments, combined cylindrical treatments, and combined Cross-Cylinder and spherical equivalent (SEQ) treatments. Both authors concluded that combined spherical and hyperopic cylindrical or combined cylindrical approaches result in reduced ablation depth for treating compound hyperopic and mixed astigmatism whereas applying a hyperopic sphere combined with a myopic cylinder incurs the largest amount of central and peripheral corneal tissue ablation. (Azar&Primack 2000) Despite these important theoretical publications, the definitions and differences between Bitoric and Cross-Cylinder treatments remain unclear in various publications. (Hasaballa et al. 2003, Gatinel et al 2002, Doane&Slade 2003) . For this reason, we attempt to provide a guideline for refractive surgeons including a subclassification of mixed astigmatism and a generalised Bitoric formula. Furthermore, we compare and contrast Bitoric, Cross-Cylinder and combined spherical and cylindrical

Treating Mixed Astigmatism – A Theoretical Comparison and Guideline for Combined Ablation Strategies and Wavefront Ablation