Comparison of ray-tracing method and thin-lens formula in intraocular lens power calculations
Received 29 May 2008; received in revised form 5 December 2008; accepted 17 December 2008.
Purpose
To compare the accuracy of the thin-lens and ray-tracing methods in intraocular lens (IOL) power calculations in normal eyes and eyes after corneal refractive surgery.
Setting
International Vision Correction Research Centre, University of Heidelberg, Heidelberg, Germany.
Methods
Pseudophakic eye models were constructed using Zemax optical software, importing corneal radii (normal ray tracing) and corneal surface elevation data (individual ray tracing) measured by Pentacam Scheimpflug photography. Algorithms to predict IOL position (effective lens position [ELP]) or postoperative anterior chamber depth [ACDpost]) (Haigis, Hoffer Q, Norrby, Olsen 2) were used in the thin-lens and ray-tracing methods. Intraocular lens power was calculated in 25 eyes after corneal refractive surgery using normal and double-K modified thin-lens and ray-tracing methods.
Results
Back-calculation of ELP and ACDpost were well correlated. Using algorithms of Haigis, Hoffer Q, Norrby, and Olsen 2 to predict IOL position, mean absolute prediction errors (MAEs) of the thin-lens formula were 0.64 diopters (D) ± 0.52 (SD), 0.57 ± 0.46 D, 0.59 ± 0.42 D, and 0.61 ± 0.47 D, respectively; MAEs of normal ray-tracing method were 0.64 ± 0.50 D, 0.58 ± 0.44 D, 0.59 ± 0.41 D, and 0.62 ± 0.45 D, respectively; MAEs of individual ray-tracing method were 0.66 ± 0.52 D, 0.59 ± 0.45 D, 0.59 ± 0.43 D, and 0.62 ± 0.50 D, respectively. No statistical differences were found between the thin-lens and ray-tracing methods.
Conclusion
Theoretical thin-lens formulas were as accurate as the ray-tracing method in IOL power calculations in normal eyes and eyes after refractive surgery.
From the International Vision Correction Research Centre (Jin, Rabsilber, Ehmer, Borkenstein, Limberger, Auffarth), Department of Ophthalmology, University of Heidelberg, Germany; Department of Ophthalmology (Jin, Guo), Guangdong Provincial People's Hospital, Guangzhou, China
Corresponding author: Gerd U. Auffarth, MD, International Vision Correction Research Centre, Department of Ophthalmology, University of Heidelberg, INF 400, 69120, Heidelberg, Germany.
No author has a financial or proprietary interest in any material or method mentioned.
Presented in part at the 22. Kongress der Deutschsprachige Gesellschaft für Intraokularlinsen-Implantation, Interventionelle und Refraktive Chirurgie, Heidelberg, Germany, February 2008, and the 21. Internationaler Kongress der Deutschen Ophthalmochirugen, Nuremberg, Germany, June 2008.
ABSTRACT