Figure 2

(a) A virtual cross cylinder for anterior corneal astigmatism with axis α. The power profile is expressed as FACA(φ) = − 0.5 × ACA × cos2(φ – α). (b) A virtual cross cylinder for posterior corneal astigmatism with axis β. The power profile is expressed as FPCA(φ) = − 0.5 × PCA × cos2(φ – β). ACA magnitude of the anterior corneal astigmatism, PCA magnitude of the posterior corneal astigmatism.