Intraocular Lens Power Prediction in Patients Who Undergo Cataract Surgery Following Previous Radial Keratotomy

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Abstract
Background: Previous experience has shown that there is no technical difficulty in performing cataract surgery on patients who have previously undergone radial keratotomy. However, some researchers have reported inaccuracy in intraocular lens (IOL) power selection. Objectives: To assess the visual and refractive outcomes of our patients and to compare different formulas and variables to improve accuracy in power determination. Main Outcome Measures: Ten eyes subjected to phacoemulsification with in-the-bag posterior chamber lens implantation 79 months (range, 36-118 months) after radial keratotomy were evaluated in this study. The IOL power was retrospectively calculated for each eye using the Binkhorst, SRK II, and Holladay formulas with the current keratometry reading, the refractive-derived keratometric value (K), the current refractive-derived K, and the adjusted K. The final refractive result was used as a criterion to judge the accuracy and predictability for each approach. Results: Three eyes underwent an IOL exchange after initial surgery. Among the 7 eyes that did not undergo an IOL exchange, a hyperopic shift that regressed approximately 3 months after surgery occurred in the early post-operative period. At the final examination, 5 of the 7 eyes had a hyperopic error, with 2 eyes showing more than 1.00 diopter (D). Overall, in an average of 27 months (range, 9-80 months) of follow-up, an uncorrected visual acuity of 20/40 or better was obtained in 6 (60%) of the eyes. All 10 eyes had a 20/25 or better postoperative best-corrected visual acuity. The mean (±SD) spherical equivalent refraction was changed from −0.78±3.49 D preoperatively to 0.45±1.31 D postoperatively. We found that the Binkhorst and Holladay formulas are more accurate than the SRK II formula. With the use of an adjusted K (ie, the current average K minus 1.0 D) in combination with the Binkhorst and Holladay formulas, most of the eyes would achieve a refraction of −2.00 to +0.50 D. Conclusions: A corneal flattening effect caused by cataract surgery tends to occur in eyes that have undergone previous radial keratotomy. The use of an average between the Binkhorst and Holladay formulas, aiming for −0.75 D with an adjusted K, seems to be a more accurate and predictable method for IOL power calculation. This approach could reduce the chance of postoperative hyperopia.