Intraocular lens power calculation using ray tracing following excimer laser surgery

Abstract

Purpose To evaluate intraocular lens (IOL) power calculation using ray tracing in patients presenting with cataract after excimer laser surgery. Methods Ten eyes of seven consecutive patients who presented for cataract surgery following excimer laser treatment without any pre-refractive biometry data were enrolled in this prospective clinical study. Preoperatively, IOL power calculation was performed using a ray tracing software called OKULIX. Keratometry data (C-Scan) were imported and axial length (IOLMaster) was entered manually. Accuracy of IOL power calculation was investigated by subtracting attempted and achieved spherical equivalent. Conclusions IOL power calculation after excimer laser surgery can be difficult, especially when pre-refractive keratometry values are not available. In these cases, ray tracing combined with corneal topography measurements provides reliable and satisfactory postoperative results. However, it is advisable to be careful when calculating IOL power for eyes with corneal radii exceeding 10 mm because of slightly higher prediction errors.

Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula

“…Masket and Masket 6 report 30 eyes, Latkany et al 8 21 eyes, Rosa et al 9 19 cases, Einighammer et al 21 12 eyes, Walter et al 7 9 eyes, Shammas and Shammas 3 15 eyes, and Rabsilber et al 23 10 eyes. It seems as though the 22 ME 0.08 G 0.62, 4 ME 0.14 D, 23 and ME À0.15 G 0.29 D. 6 Shammas and Shammas' 3 results (ME 0.003 G 0.63 D, MA 0.55 G 0.31 D) are given for the IOL prediction error; converted to refraction prediction errors, these numbers are even smaller.…”

Use of Scheimpflug corneal anterior-posterior imaging in ray-tracing intraocular lens power calculation

“…The accuracy of OKULIX was comparable with the SRK/T formula in normal cataractous eyes (Preußner et al. 2005, 2008), although it significantly improved in postcorneal surgery cases (Rabsilber et al. 2007).…”

Estimation of true corneal power after keratorefractive surgery in eyes requiring cataract surgery: BESSt formula

“…The results using the BESSt formula compared favorably with those obtained with ray-tracing technology combined with corneal topography (mean error 0.31 G 0.84 D versus 0.08 G 0.62 D). 30 However, ray-tracing may be associated with unpredictability if applied to corneas with radii of curvature O10.0 mm. Other nomogram-based techniques 3,31,32 seem to perform better than the BESSt This difference in measurement may be explained by the fact that whereas the Gaussian optics formula should theoretically measure total corneal power, standard keratometry measurement may not take into full account the (negative) posterior corneal power.…”