Emmetropia Verifying Optical (EVO) Formula

The origins of the Emmetropia Verifying Optical (EVO) formula (versions 1.0 and 2.0) are described. This is a thick lens formula based on Gaussian optics principles; it considers the anterior and posterior corneal curvatures, central corneal thickness, as well as the geometry of the intraocular lens (IOL). The formula modifies the axial length measured by optical biometry, calculates the total corneal power using Gaussian thick lens equations and calculates the principal planes of the IOL based on its geometry. The performance of the EVO formula, its toric calculator and the formula version for post-myopic laser vision correction eyes are reported in a review of published papers.