Reliability of a new correcting factor in calculating intraocular lens power after refractive corneal surgery

Purpose: To test the reliability of a corneal radius correcting factor (R factor) in calculating intraocular lens (IOL) power in eyes that developed cataract after refractive surgery and compare it with the clinical history (CHM) and double-K (DKM) methods. Setting: Department of Ophthalmology, Second University of Naples, Naples, Italy. Methods: Nineteen eyes from the literature that underwent cataract extraction and IOL implantation after refractive surgery were used to compare actual postoperative and expected refractive errors utilizing the R factor, CHM, and DKM. Intraocular lens powers were calculated with 3 formulas: SRK/T, Hoffer Q and Holladay 1. The differences were evaluated with the Wilcoxon test and Spearman correlation. Results: With the R factor SRK/T and Holladay 1 formulas gave the best results; 16 (84.2%) and 17 (89.5%) eyes were within 62 diopters (D) of emmetropia. With CHM, the best results were obtained using the SRK/T and Holladay 1 formulas; with both formulas 12 (63.2%) eyes were within 62 D of emmetropia. With DKM, the best results were obtained using SRK/T and Holladay 1 formulas; with both formulas 10 eyes (52.63%) were in the range of 62 D from emmetropia. Conclusions: The R factor can be used with the SRK/T or Holladay 1 formula because this method seems comparable or superior to DKM and CHM