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      IOL Power Calculation after Corneal Refractive Surgery

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          Abstract

          Purpose. To describe the different formulas that try to overcome the problem of calculating the intraocular lens (IOL) power in patients that underwent corneal refractive surgery (CRS). Methods. A Pubmed literature search review of all published articles, on keyword associated with IOL power calculation and corneal refractive surgery, as well as the reference lists of retrieved articles, was performed. Results. A total of 33 peer reviewed articles dealing with methods that try to overcome the problem of calculating the IOL power in patients that underwent CRS were found. According to the information needed to try to overcome this problem, the methods were divided in two main categories: 18 methods were based on the knowledge of the patient clinical history and 15 methods that do not require such knowledge. The first group was further divided into five subgroups based on the parameters needed to make such calculation. Conclusion. In the light of our findings, to avoid postoperative nasty surprises, we suggest using only those methods that have shown good results in a large number of patients, possibly by averaging the results obtained with these methods.

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          Most cited references81

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          Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula.

          To describe the Haigis-L formula for the calculation of intraocular lenses (IOLs) after refractive laser surgery for myopia based on current biometry and keratometry and present clinical results. University Eye Hospital, Wuerzburg, Germany, and various clinics and private practices. The basic concepts of the new algorithm were described and summarized. The Haigis formula was analyzed with respect to its usability for eyes after laser surgery for myopia and modified accordingly. Correction curves for IOLMaster keratometry were derived from previous studies. The new formula was checked using the postoperative results of 187 cataract procedures in which 32 IOL types were implanted by 57 surgeons. Input data were current IOLMaster biometry as follows: axial length (AL), anterior chamber depth (ACD), and keratometry (corneal radii) measurements. Before IOL surgery, the mean spherical equivalent was -7.60 diopters (D)+/-3.90 (SD) (range -20.00 to -1.25 D); the mean AL, 27.02+/-2.01 mm (range 23.09 to 35.32 mm); the mean ACD, 3.52 +/- 0.36 mm (range 2.43 to 4.39 mm); and the mean of the measured corneal radii, 8.70+/-0.60 mm (range 7.28 to 10.96 mm). The mean arithmetic refractive prediction error was -0.04+/-0.70 D (range -2.30 to +2.40 D) and the median absolute error, 0.37 D (range +0.01 to +2.40 D). The percentages of correct refraction predictions within +/-2.00, +/-1.00, and +/-0.50 D were 98.4%, 84.0%, and 61.0%, respectively. The new formula would produce promising results in eyes without refractive history. Its refractive predictability fulfills the current criteria for normal eyes.
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            Intraocular lens power calculation after corneal refractive surgery: double-K method.

            To determine the accuracy of a method of calculating intraocular lens (IOL) power after corneal refractive surgery. Department of Ophthalmology, Hospital de Gipuzkoa, San Sebastián, Spain. The SRK/T formula was modified to use the pre refractive surgery K-value (Kpre) for the effective lens position (ELP) calculation and the post refractive surgery K-value (Kpost) for IOL power calculation by the vergence formula. The Kpre value was obtained by keratometry or topography and the Kpost, by the clinical history method. The formula was assessed in 9 cases of cataract surgery after laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) in which all relevant data were available. Refractive results of the standard SRK/T and the double-K SRK/T were compared statistically. The mean IOL power for emmetropia and the achieved refraction (mean spherical equivalent [SE]), respectively, were +17.85 diopters (D) +/- 3.43 (SD) and +1.82 +/- 0.73 with the standard SRK/T and +20.25 +/- 3.55 D and +0.13 +/- 0.62 D with the double-K SRK/T. No case in the standard SRK/T group and 6 cases (66.66%) in the double-K group achieved a +/-0.5 D SE. Double-K modification of the SRK/T formula improved the accuracy of IOL power calculation after LASIK and PRK.
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              Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy.

              To assess the validity of corneal power measurement and standard intraocular lens power (IOLP) calculation after photorefractive keratectomy (PRK). Nonrandomized, prospective, cross-sectional, clinical study. A total of 31 eyes of 21 females and 10 males with a mean age at the time of surgery of 32.3 +/- 6.6 years (range, 24.4-49.5 years). Subjective refractometry, standard keratometry, TMS-1 corneal topography analysis, and pachymetry were performed before and 15.8 +/- 10.4 months after PRK for myopia (n = 24, -1 .5 to -8.0 diopters [D], mean -5.4 +/- 1.9 D) or myopic astigmatism (n = 7, sphere -2.0 to -7.5 D, mean -4.4 +/- 1.9 D; cylinder -1.0 to -3.0 D, mean -1.9 +/- 0.7 D). The IOLP calculations were done using two different formulas (SRK/T and HAIGIS). Keratometric power (K) and topographic simulated keratometric power (TOPO) as measured (Kmeas, TOPOmeas) and as calculated according to the change of power of the anterior corneal surface or according to the spherical equivalent change after PRK (Kcalc, TOPOcalc), IOLP for emmetropia, and postoperative ametropia for calculated corneal powers were assessed in a model. After PRK, mean Kmeas and TOPOmeas were significantly greater (0.4-1.4 D, maximum 3.3 D) than mean KRcalc and TOPOcalc (P 1 D) than IOLP values using topographic readings (P < 0.0001). The theoretically induced mean refractive error after cataract surgery ranged from +0.4 to +1.4 (maximum, +3.1) D. Corneal power overestimation and IOLP underestimation correlated significantly with the spherical equivalent change after PRK (P = 0.001) and the intended ablation depth during PRK (P = 0.004). To avoid underestimation of IOLP and hyperopia after cataract surgery following PRK, measured corneal power values must be corrected. The calculation method using spherical equivalent change of refraction at the corneal plane seems to be the most appropriate method. In comparison with this method, direct power measurements underestimate corneal flattening after PRK by 24% on average. Use of conventional topography analysis seems to increase the risk of error. However, because this study is retrospective and theoretical, there is still a need for a large prospective investigation to validate the authors' findings.
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                Author and article information

                Journal
                Biomed Res Int
                Biomed Res Int
                BMRI
                BioMed Research International
                Hindawi Publishing Corporation
                2314-6133
                2314-6141
                2014
                21 July 2014
                : 2014
                : 658350
                Affiliations
                1Department of Medicine and Surgery, University of Salerno, Via Salvatore Allende1, Baronissi, 84081 Salerno, Italy
                2U.O.C. Corneal Transplant Unit, Pellegrini Hospital, 80100 Naples, Italy
                3U.O.C. Eye Day Surgery, De Luca e Rossano Hospital, 80069 Vico Equense, Italy
                Author notes

                Academic Editor: Ciro Costagliola

                Author information
                http://orcid.org/0000-0001-8301-9417
                Article
                10.1155/2014/658350
                4129218
                25136609
                cc174c4f-74c5-4717-bc9f-20c715dd9d99
                Copyright © 2014 Maddalena De Bernardo et al.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 23 May 2014
                : 3 July 2014
                Categories
                Review Article

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