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      Estimation of Intraocular Lens Power Calculation after Myopic Corneal Refractive Surgery: Using Corneal Height in Anterior Segment Optical Coherence Tomography

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          Abstract

          Purpose

          To investigate the feasibility of estimating effective lens position (ELP) and calculating intraocular lens power using corneal height (CH), as measured using anterior segment optical coherence tomography (AS-OCT), in patients who have undergone corneal refractive surgery.

          Methods

          This study included 23 patients (30 eyes) who have undergone myopic corneal refractive surgery and subsequent successful cataract surgery. The CH was measured with AS-OCT, and the measured ELP (ELP m) was calculated. Intraocular lens power, which could achieve actual emmetropia (P real), was determined with medical records. Estimated ELP (ELP est) was back-calculated using P real, axial length, and keratometric value through the SRK/T formula. After searching the best-fit regression formula between ELP m and ELP est, converted ELP and intraocular lens power (ELP conv, P conv) were obtained and then compared to ELP est and P real, respectively. The proportion of eyes within a defined error was investigated.

          Results

          Mean CH, ELP est, and ELP m were 3.71 ± 0.23, 7.74 ± 1.09, 5.78 ± 0.26 mm, respectively. The ELP m and ELP est were linearly correlated (ELP est = 1.841 × ELP m - 2.018, p = 0.023, R = 0.410) and ELP conv and P conv agreed well with ELP est and P real, respectively. Eyes within ±0.5, ±1.0, ±1.5, and ±2.0 diopters of the calculated P conv, were 23.3%, 66.6%, 83.3%, and 100.0%, respectively.

          Conclusions

          Intraocular lens power calculation using CH measured with AS-OCT shows comparable accuracy to several conventional methods in eyes following corneal refractive surgery.

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          Most cited references 35

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          The Hoffer Q formula: a comparison of theoretic and regression formulas.

           Barry Hoffer (1993)
          A new formula, the Hoffer Q, was developed to predict the pseudophakic anterior chamber depth (ACD) for theoretic intraocular lens (IOL) power formulas. It relies on a personalized ACD, axial length, and corneal curvature. In 180 eyes, the Q formula proved more accurate than those using a constant ACD (P < .0001) and equal (P = .63) to those using the actual postoperative measured ACD (which is not possible clinically). In 450 eyes of one style IOL implanted by one surgeon, the Hoffer Q formula was equal to the Holladay (P = .65) and SRK/T (P = .63) and more accurate than the SRK (P < .0001) and SRK II (P = .004) regression formulas using optimized personalization constants. The Hoffer Q formula may be clinically more accurate than the Holladay and SRK/T formulas in eyes shorter than 22.0 mm. Even the original nonpersonalized constant ACD Hoffer formula compared with SRK I (using the most valid possible optimized personal A-constant) has a better mean absolute error (0.56 versus 0.59) and a significantly better range of IOL prediction error (3.44 diopters [D] versus 7.31 D). The range of error of the Hoffer Q formula (3.59 D) was half that of SRK I (7.31 D). The highest IOL power errors in the 450 eyes were in the SRK II (3.14 D) and SRK I (6.14 D); the power error was 2.08 D using the Hoffer Q formula. The series using overall personalized ACD was more accurate than using an axial length subgroup personalized ACD in each axial length subgroup. The results strongly support replacing regression formulas with third-generation personalized theoretic formulas and carefully evaluating the Holladay, SRK/T, and Hoffer Q formulas.
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            Development of the SRK/T intraocular lens implant power calculation formula.

            A new implant power calculation formula (SRK/T) was developed using the nonlinear terms of the theoretical formulas as its foundation but empirical regression methodology for optimization. Postoperative anterior chamber depth prediction, retinal thickness axial length correction, and corneal refractive index were systematically and interactively optimized using an iterative process on five data sets consisting of 1,677 posterior chamber lens cases. The new SRK/T formula performed slightly better than the Holladay, SRK II, Binkhorst, and Hoffer formulas, which was the expected result as any formula performs superiorly with the data from which it was derived. Comparative accuracy of this formula upon independent data sets is addressed in a follow-up report. The formula derived provides a primarily theoretical approach under the SRK umbrella of formulas and has the added advantage of being calculable using either SRK A-constants that have been empirically derived over the last nine years or using anterior chamber depth estimates.
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              Formula choice: Hoffer Q, Holladay 1, or SRK/T and refractive outcomes in 8108 eyes after cataract surgery with biometry by partial coherence interferometry.

              To assess how intraocular lens (IOL) formula choice affects refractive outcomes after cataract surgery using IOLMaster biometry. Department of Ophthalmology, Gloucestershire Hospitals NHS Foundation Trust, Cheltenham, United Kingdom. Database study. Hypothetical prediction errors were retrospectively calculated on prospectively collected data from electronic medical records using optimized Hoffer Q, Holladay 1, and SRK/T formulas (Sofport AO and Akreos Fit IOLs) across a range of 0.5 mm or 1.0 mm axial length (AL) subgroups. In short eyes, the Hoffer Q had the lowest mean absolute error (MAE) for ALs from 20.00 to 20.99 mm. The Hoffer Q and Holladay 1 had a lower MAE than the SRK/T for ALs from 21.00 to 21.49 mm. There were no statistically significant differences in MAE for ALs from 21.50 to 21.99 mm. In medium eyes, there were no statistically significant differences in MAE for any IOL formula for ALs from 22.00 to 23.49 mm. For ALs from 23.50 to 25.99 mm, there was a trend toward lower MAEs for the Holladay 1, with statistically significant differences in 2 subgroups. In long eyes, the SRK/T had the lowest MAE, with statistically significant differences for ALs of 27.00 mm or longer. The Hoffer Q performed best for ALs from 20.00 to 20.99 mm, the Hoffer Q and Holladay 1 for ALs from 21.00 to 21.49 mm, and the SRK/T for ALs of 27.00 mm or longer. Using optimized constants, refractive outcomes of 40%, 75%, and 95% within ±0.25 diopter (D), ±0.50 D, and ±1.00 D, respectively, were achievable. No author has a financial or proprietary interest in any material or method mentioned. Additional disclosure is found in the footnotes. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.
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                Author and article information

                Journal
                Korean J Ophthalmol
                Korean J Ophthalmol
                KJO
                Korean Journal of Ophthalmology : KJO
                The Korean Ophthalmological Society
                1011-8942
                2092-9382
                June 2015
                20 May 2015
                : 29
                : 3
                : 195-202
                Affiliations
                [1 ]Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.
                [2 ]Laboratory of Ocular Regenerative Medicine and Immunology, Seoul Artificial Eye Center, Seoul National University Hospital Clinical Research Institute, Seoul, Korea.
                Author notes
                Corresponding Author: Mee Kum Kim, MD. Department of Ophthalmology, Seoul National University College of Medicine, 103 Daehak-ro, Jongno-gu, Seoul 110-799, Korea. Tel: 82-2-2072-2665, Fax: 82-2-741-3187, kmk9@ 123456snu.ac.kr
                Article
                10.3341/kjo.2015.29.3.195
                4446561
                © 2015 The Korean Ophthalmological Society

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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