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      Intraocular lens power calculation following laser refractive surgery

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          Abstract

          Refractive outcomes following cataract surgery in patients that have previously undergone laser refractive surgery have traditionally been underwhelming. This is related to several key issues including the preoperative assessment (keratometry) and intraocular lens power calculations. Peer-reviewed literature is overwhelmed by the influx of methodology to manipulate the corneal or intraocular lens (IOL) powers following refractive surgery. This would suggest that the optimal derivative formula has yet been introduced. This review discusses the problems facing surgeons approaching IOL calculations in these post-refractive laser patients, the existing formulae and programs to address these concerns. Prior published outcomes will be reviewed.

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          Most cited references77

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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.
          Article 0 comments Cited 114 times – based on 0 reviews     Review now
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            Development of the SRK/T intraocular lens implant power calculation formula.

            A Retzlaff, Robert Sanders, M Tanofsky-Kraff (1990)
            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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              Benchmark standards for refractive outcomes after NHS cataract surgery.

              B Zuberbuhler, Jonathon R. Johnston, M McKibbin … (2008)
              To establish benchmark standards for refractive outcome after cataract surgery in the National Health Service when implementing the 2004 biometry guidelines of the Royal College of Ophthalmologists and customising A constants. Three cycles of prospective data were collected throughout the cataract care pathway on all patients using an electronic medical record system (Medisoft Ophthalmology), between January 2003 and February 2006. The electronic medical record automatically recommends the formula to be used according to the College guidelines and allows A constants to be customised separately for either ultrasound or partial coherence interferometry methods of axial length measurement and for different intraocular lens models. Consultants and trainees performed routine phacoemulsification cataract surgery and new intraocular lens models were introduced during the cycles. Uncomplicated cases with 'in-the-bag fixation', achieving 6/12 Snellen acuity or better were included. Community ophthalmic opticians performed refraction at 4 weeks. The postoperative subjective refraction was within 1 D of the predicted value in 79.7% of the 952 cases in cycle 1, 83.4% of 2406 cases in cycle 2, and 87.0% of 1448 cases in cycle 3. On the basis of our data, using College formula, optimising A constants and partial coherence interferometry, a benchmark standard of 85% of patients achieving a final spherical equivalent within 1 D of the predicted figure and 55% of patients within 0.5 D should be adopted.
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                Author and article information

                Contributors
                Christopher Hodge: christopher.hodge@visioneyeinstitute.com.au
                Colm McAlinden: colm.mcalinden@gmail.com
                Michael Lawless: michael.lawless@visioneyeinstitute.com.au
                Colin Chan: colin.chan@visioneyeinstitute.com.au
                Gerard Sutton: gerard.sutton@visioneyeinstitute.com.au
                Aifric Martin: aifric2001@yahoo.co.uk
                Journal
                Journal ID (nlm-ta): Eye Vis (Lond)
                Journal ID (iso-abbrev): Eye Vis (Lond)
                Title: Eye and Vision
                Publisher: BioMed Central (London )
                ISSN (Electronic): 2326-0254
                Publication date (Electronic): 2 April 2015
                Publication date PMC-release: 2 April 2015
                Publication date Collection: 2015
                Volume: 2
                Electronic Location Identifier: 7
                Affiliations
                [ ]Vision Eye Institute, Level 3 270 Avenue Chatwood, Victoria, NSW Australia
                [ ]Save Sight Institute, University of Sydney, Sydney, NSW Australia
                [ ]Flinders University, Bedford Park, Adelaide, South Australia Australia
                [ ]Wenzhou Medical College, Wenzhou, Zhejiang China
                [ ]School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
                [ ]University College Dublin, Montrose, Dublin Ireland
                Article
                Publisher ID: 17
                DOI: 10.1186/s40662-015-0017-3
                PMC ID: 4655459
                PubMed ID: 26605363
                SO-VID: c4719caf-f2c9-484b-844e-81482668be40
                Copyright © © Hodge et al.; licensee BioMed Central. 2015
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. 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
                Date received : 19 November 2014
                Date accepted : 11 March 2015
                Categories
                Subject: Review
                Custom metadata
                issue-copyright-statement © The Author(s) 2015

                Keywords: cataract,laser refractive surgery,intraocular lens calculations
                Data availability:
                Keywords: cataract, laser refractive surgery, intraocular lens calculations

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