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Calculation of the skewed radial axis index, which corresponds to the angle (α) formed between the two steepest semimeridians above and below the horizontal meridian. The SRAX is equal to 180 minus the smaller of the two angles formed by the radii of the semimeridians. The below algorithm for calculating the composite KISA% index. Abbreviations: K: keratometry value; I-S: inferior-superior asymmetry index; AST: degree of regular astigmatism; SRAX: skewed radial axis index
