The Olsen Formula

The ambition of the Olsen formula was to develop a thick-lens formula based on paraxial ray tracing as assumption-free as possible allowing for a full-thickness calculation of the cornea and the IOL power and the use of real physical dimensions—including the physical position of the IOL—to be used in the formula. From 2012, the Olsen formula was modified to allow exact ray tracing on aspheric surfaces to include the effect of spherical aberration. The prediction of the IOL position has been improved over the years based on numerous clinical measurements of the actual IOL position and the correlation with relevant preoperative clinical parameters (see chapter on ELP estimation). An important step was the development of the C-constant concept which predicts the IOL position as a fraction of the preoperative lens thickness, thereby reducing the number of indirect parameters in the algorithm.