Fig. 1

Achieved correction vs. Attempted correction with Nomogram 1. The achieved spherical change (considering astigmatism as a negative convention) correlated with the attempted change (p < 0.0001), and the magnitude of the achieved cylindrical change (vectorial analysis with astigmatism as the negative convention) correlated with the attempted change (p < 0.0001). The nomogram correction differs significantly from the preoperative refraction for sphere (p < 0.0001) but not for astigmatism (p = 0.3). The nomogram proposes a − 6% reduction in sphere with a − 0.4 D bias, and a + 1% enhancement of the cylinder. A refraction of − 2.50 D sphere with − 1.50 D astigmatism at 63 degrees should be planned as − 2.77 D sphere with − 1.52 D astigmatism at 63 degrees