Fig. 6

Achieved correction vs. Attempted correction with Nomogram 7. The achieved spherical equivalent change correlated with the attempted change (p < 0.0001) and the absolute magnitude of the achieved cylindrical change (separate cardinal and oblique components analyses) with the attempted change (p < 0.0001 for cardinal astigmatism; p < 0.0001 for oblique astigmatism). The nomogram correction differs significantly from the preoperative refraction for sphere (p < 0.0001) and for cardinal astigmatism (p < 0.005) but not for oblique astigmatism (p = 0.1). The nomogram proposes a − 5% reduction in sphere with a − 0.41 D bias, a + 1% enhancement of the cardinal astigmatism with a + 0.03 D bias, and a − 8% reduction of the oblique astigmatism with a + 0.01 D bias. A refraction of − 2.50 D sphere with − 1.50 D astigmatism at 63 degrees should be planned as − 2.78 D sphere with − 1.47 D astigmatism at 66 degrees