Acdsee 4.0 powerpack suite serial
Ray tracing involves the direct calculation of refraction of rays of light at each medium change within the eye using Snell’s law. Numerical ray tracing represents an alternative to Gaussian optics for the purpose of IOL power calculation. Achieving an accurate prediction of the optimal ELP for all patients is a more challenging task, however, and represents an ongoing limitation for modern formulas. 1 4 The optimal ELP in a given eye can be back-calculated with knowledge of the eye’s postoperative refraction. In practice, however, the postoperative ACD and the optimal location of the principal plane of the IOL in a given formula’s optical model of the eye are not numerically equal. 3 First introduced by Holladay in 1993, 3 ELP was initially intended to estimate the position of the IOL in the postoperative eye. The primary empirical adjustments for these modern formulas (such as Barrett Universal II, Holladay 2 and SRK/T) are made through the use of effective lens position (ELP) as an intermediate quantity to indicate the location of the lens as it relates to a given optical model of the eye. Most modern IOL calculation formulas involve computation of postoperative refraction using Gaussian optics, which relies on the assumption that incoming rays are paraxial, in addition to empirically determined adjustment factors. As more biometric variables have become available, additional preoperative measurements such as the axial length and corneal power have been added to methods for estimating the postoperative IOL position. First-generation lens calculation formulas represented postoperative ACD by a constant. 1 2 Methods for predicting postoperative ACD have evolved over the past several decades. Inaccuracy in prediction of the postoperative anterior chamber depth (ACD) has been reported to be the primary remaining source of error in IOL power calculations. Postoperative intraocular lens (IOL) position estimation is essential to IOL power calculations for cataract surgery.