RESUMEN
Purpose: To evaluate the accuracy of intraocular lens (IOL) power prediction of the formulas available on the American Society of Cataract and Refractive Surgery (ASCRS) post?refractive calculator in eyes with prior radial keratotomy (RK) for myopia. Methods: This retrospective study included 25 eyes of 18 patients whose status was post?RK for treatment of myopia, which had undergone cataract extraction with IOL implantation. Prediction error was calculated as the difference between implanted IOL power and predicted power by various formulae available on ASCRS post?refractive calculator. The formulas compared were Humphrey Atlas method, IOLMaster/Lenstar method, Barrett True?K no?history formula, ASCRS Average power, and ASCRS Maximum power on ASCRS post?refractive calculator. Results: Median absolute errors were the least for Barrett True?K and ASCRS Maximum power, that is, 0.56 (0.25, 1.04) and 0.56 (0.25, 1.06) D, respectively, and that of Atlas method was 1.60 (0.85, 2.28) D. Median arithmetic errors were positive for Atlas, Barrett True?K, ASCRS Average (0.86 [?0.17, 1.61], 0.14 [?0.22 to 0.54], and 0.23 [?0.054, 0.76] D, respectively) and negative for IOLMaster/Lenstar method and ASCRS Maximum power (?0.02 [?0.46 to 0.38] and ? 0.48 [?1.06 to ? 0.22] D, respectively). Multiple comparison analysis of Friedman抯 test revealed that Atlas formula was significantly different from IOLMaster/ Lenstar, Barrett True?K, and ASCRS Maximum power; ASCRS Maximum power was significantly different from all others (P < 0.00001). Conclusion: In post?RK eyes, Barrett True?K no?history formula and ASCRS Maximum power given by the ASCRS calculator were more accurate than other available formulas, with ASCRS Maximum leading to more myopic outcomes when compared to others
RESUMEN
Purpose: To develop a nomogram in cases with mismatch between subjective and Topolyzer cylinder, and based on the magnitude of the mismatch, customize a treatment plan to attain good visual outcomes post?laser?assisted in situ keratomileusis (LASIK) surgery. Methods: The patients were evaluated preoperatively using corneal tomography with Pentacam. Five optimal corneal topography scans were obtained from the Topolyzer Vario were used for planning the LASIK treatment. For the nomogram purpose, the patients were divided into three categories based on the difference between the subjective cylinder and Topolyzer (corneal) cylinder. The first group (group 1) consisted of eyes of patients, where the difference was less than or equal to 0.4 D. The second group (group 2) consisted of eyes, where the difference was more than 0.4 D and the subjective cylinder was lesser than the Topolyzer cylinder. The third group (group 3) included eyes where the difference was more than 0.4 D but the subjective cylinder was greater than the Topolyzer cylinder. LASIK was performed with the WaveLight FS 200 femtosecond laser and WaveLight EX500 excimer laser. Assessment of astigmatism correction for the three groups was done using Aplins vector analysis. For comparison of proportions, Chi?square test was used. A P value less than 0.05 was considered statistically significant. Results: The UDVA was statistically significantly different when compared between groups 1 and 2 (P = 0.02). However, the corrected distance visual acuity (CDVA) was similar among all the three groups (P = 0.1). Group 3 showed an increase of residual cylinder by ?0.25 D, which was significant at intermediate and near reading distances (P < 0.05). Group 3 showed significantly higher target?induced astigmatism (TIA) compared to groups 1 and 2 (P = 0.01). The mean surgically induced astigmatism (SIA) was the least in group 2, which was statistically significant (P < 0.01). Conclusion: The outcomes for distance vision using our nomogram postoperatively were excellent, but further refinement for improving the near vision outcomes is required