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      Intraocular lens power calculation in eyes with previous corneal refractive surgery

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          Abstract

          Background

          This review aims to explain the reasons why intraocular lens (IOL) power calculation is challenging in eyes with previous corneal refractive surgery and what solutions are currently available to obtain more accurate results.

          Review

          After IOL implantation in eyes with previous LASIK, PRK or RK, a refractive surprise can occur because i) the altered ratio between the anterior and posterior corneal surface makes the keratometric index invalid; ii) the corneal curvature radius is measured out of the optical zone; and iii) the effective lens position is erroneously predicted if such a prediction is based on the post-refractive surgery corneal curvature. Different methods are currently available to obtain the best refractive outcomes in these eyes, even when the perioperative data (i.e. preoperative corneal power and surgically induced refractive change) are not known. In this review, we describe the most accurate methods based on our clinical studies.

          Conclusions

          IOL power calculation after myopic corneal refractive surgery can be calculated with a variety of methods that lead to relatively accurate outcomes, with 60 to 70% of eyes showing a prediction error within 0.50 diopters.

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          Most cited references61

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          Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis.

          The precision of intraocular lens (IOL) calculation is essentially determined by the accuracy of the measurement of axial length. In addition to classical ultrasound biometry, partial coherence interferometry serves as a new optical method for axial length determination. A functional prototype from Carl Zeiss Jena implementing this principle was compared with immersion ultrasound biometry in our laboratory. In 108 patients attending the biometry laboratory for planning of cataract surgery, axial lengths were additionally measured optically. Whereas surgical decisions were based on ultrasound data, we used postoperative refraction measurements to calculate retrospectively what results would have been obtained if optical axial length data had been used for IOL calculation. For the translation of optical to geometrical lengths, five different conversion formulas were used, among them the relation which is built into the Zeiss IOL-Master. IOL calculation was carried out according to Haigis with and without optimization of constants. On the basis of ultrasound immersion data from our Grieshaber Biometric System (GBS), postoperative refraction after implantation of a Rayner IOL type 755 U was predicted correctly within +/- 1 D in 85.7% and within +/- 2 D in 99% of all cases. An analogous result was achieved with optical axial length data after suitable transformation of optical path lengths into geometrical distances. Partial coherence interferometry is a noncontact, user- and patient-friendly method for axial length determination and IOL planning with an accuracy comparable to that of high-precision immersion ultrasound.
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            C constant: new concept for ray tracing-assisted intraocular lens power calculation.

            To evaluate the accuracy of the C constant for ray tracing-assisted intraocular lens (IOL) power calculation.
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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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                Author and article information

                Journal
                Eye Vis (Lond)
                Eye Vis (Lond)
                Eye and Vision
                BioMed Central (London )
                2326-0254
                8 July 2018
                8 July 2018
                2018
                : 5
                : 18
                Affiliations
                [1 ]ISNI 0000 0004 1796 1828, GRID grid.420180.f, G.B. Bietti Eye Foundation, ; Rome, Italy
                [2 ]ISNI 0000 0000 9632 6718, GRID grid.19006.3e, Stein Eye Institute, , University of California, ; Los Angeles, CA USA
                [3 ]St. Mary’s Eye Center, Santa Monica, CA USA
                Author information
                http://orcid.org/0000-0003-0075-3582
                Article
                110
                10.1186/s40662-018-0110-5
                6053834
                30038922
                79c530ca-b86f-4c5b-bdf5-3df1af8d7961
                © The Author(s). 2018

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 25 March 2018
                : 22 June 2018
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/501100003196, Ministero della Salute;
                Funded by: Fondazione Roma
                Categories
                Review
                Custom metadata
                © The Author(s) 2018

                cataract,intraocular lens power,lasik,prk,excimer laser,corneal surgery,keratometry

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