Accuracy of intraocular lens calculation with ray tracing

To quantify the current accuracy limits of ray tracing for intraocular lens (IOL) calculations, compare results for spherical vs aspheric IOLs, and determine the value of using crystalline lens thickness in IOL calculations.

Of 591 eyes, 363 eyes were implanted with spherical IOLs (320 SA60AT [Alcon Laboratories Inc] and 43 Y-60H [Hoya Corp]) and 228 eyes had aspheric, aberration-correcting IOLs (57 SN60WF [Alcon Laboratories Inc], 112 Tecnis ZCB00 [Abbott Medical Optics], 21 CTAsphina404 [Carl Zeiss Meditec], and 38 iMics1 [Hoya Corp]), all calculated with OKULIX ray tracing (Tedics), based on Lenstar (Haag-Streit) measurements of axial length, corneal radii, and position and thickness of the crystalline lens. The measure of accuracy was the prediction error, ie, the difference between calculated refraction and manifest refraction (spherical equivalent) 1 month after surgery calculated as mean absolute error (MAE).

The prediction error with aspheric IOLs was lower than that with spherical IOLs (MAE 0.27 vs 0.36 D) and was lower for patients with corrected distance visual acuity (CDVA) ⩾1.0 compared to CDVA <1.0 (MAE 0.26 vs 0.38 D). For aspheric IOLs and CDVA ⩾1.0, MAE differed by a factor of two compared to spherical IOLs and CDVA <1.0 (MAE 0.21 vs 0.42 D). Taking the crystalline lens position and thickness into account improved the prediction error by ∼9% overall (MAE 0.33 vs 0.36 D) and was most beneficial in patients with aspheric lenses and CDVA ⩾1.0 (MAE improved from 0.26 to 0.21 D). All differences between the investigated subgroups were statistically significant (P<.05).

Ray tracing for IOL calculation is particularly beneficial with aspheric IOLs and in eyes with good (20/20 or better) postoperative visual acuity.