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Intraocular lens power calculation after myopic refractive surgery: theoretical comparison of different methods.

Savini G, Barboni P, Zanini M

Centro Salus, Bologna, Italy. giacomo.savini@alice.it

OBJECTIVE: To evaluate the reliability of different methods developed to calculate intraocular lens (IOL) power after corneal refractive surgery. DESIGN: Retrospective observational case series. PARTICIPANTS: Preoperative and postoperative data of all eyes that underwent myopic excimer laser surgery in a private practice (Centro Salus, Bologna, Italy) between 1999 and 2004 were reviewed. INTERVENTION: The following methods were analyzed: videokeratography, clinical history, Shammas' refraction-derived and clinically derived methods, Rosa's correcting factor, Ferrara's variable refractive index, separate consideration of anterior and posterior corneal curvature (with and without preoperative data), Feiz-Mannis' formula and nomogram, and Latkany's regression formulas (based on both average and flattest postrefractive surgery keratometry). The Holladay 1 formula was used for eyes with an axial length between 22 and 24.49 mm and the SRK-T for eyes longer than 24.49 mm. Double-K formulas were also evaluated, when applicable. Each IOL power determined with these methods was compared to a benchmark value, calculated using the preoperative axial length and corneal power and aiming for the preoperative spherical equivalent. MAIN OUTCOME MEASURE: Mean error in IOL power prediction. RESULTS: Ninety-eight eyes of 98 patients were analyzed. The double-K clinical history method, Feiz-Mannis' formula, double-K method based on separate consideration of anterior and posterior corneal curvature (with and without preoperative data), and both Latkany's regression formulas were the only methods resulting in a mean IOL power not statistically different (P>0.05) from the benchmark used for comparative purposes. CONCLUSIONS: When prerefractive surgery data are available, IOL power should be calculated using the double-K clinical history method. Alternative choices may be represented by the Feiz-Mannis' formula, Latkany's regression formulas based on average and flattest postrefractive surgery keratometry, and the double-K method based on separate consideration of anterior and posterior corneal curvatures. A variant of the latter can be used to calculate IOL power when prerefractive surgery data are not available. Further prospective studies based on patients undergoing phacoemulsification after refractive surgery are needed to validate the results of this theoretical comparison.

Published 31 July 2006 in Ophthalmology, 113(8): 1271-82.
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