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      Laser in situ keratomileusis for astigmatism ≤ 0.75 Diopter combined with low myopia: a retrospective data analysis


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          This study examined the refractive and visual outcome of wavefront-optimized laser in situ keratomileusis (LASIK) in eyes with low myopia and compound myopic astigmatism ≤ 0.75 diopter (D).


          153 eyes from 153 consecutive myopic patients (74 male, 79 female; mean age at surgery 40.4 ± 10.4 years) who had a preoperative refractive cylinder ≤ 0.75 D and a manifest sphere between -0.25 D and -2.75 D, and who had completed 4-month follow-up. Three subgroups defined by the magnitude of preoperative manifest refractive cylinder (0.25, 0.50, and 0.75 D) were formed. Manifest refraction, uncorrected and corrected visual acuity were assessed pre- and postoperatively. The astigmatic changes achieved were determined using the Alpins vector analysis.


          After 4 months (120.0 ± 27.6 days) of follow-up, a mean uncorrected distant visual acuity of 0.07 ± 0.11 logMAR and a mean manifest refraction spherical equivalent of -0.06 ± 0.56 D were found. There was no statistically significant difference in efficacy and safety between the preoperative cylinder groups. Astigmatic overcorrection for preoperative cylinder of ≤ 0.50 D was suggested by the correction index, the magnitude of error, the index of success, and the flattening index.


          Low myopic eyes with a preoperative cylinder of ≤ 0.50 D were significantly overcorrected with regard to cylinder correction when combined with low myopic LASIK. Accordingly, we are cautious in recommending full astigmatic correction for eyes with low myopia and manifest cylinder of ≤ 0.50 D.

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          Most cited references17

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          Effect of uncorrected astigmatism on vision.

          To examine the effect of uncorrected astigmatism in older adults. University vision clinic. Investigational simulation. Healthy adult presbyopes had astigmatism of 0.00 to -4.00 diopters cylinder (DC) × 90 degrees and -3.00 DC × 90, × 180, and × 45 degrees induced with spectacle lenses, with the mean spherical equivalent compensated to plano, in random order. Visual acuity was assessed binocularly using a computerized test chart at 95%, 50%, and 10% contrast. Near acuity and reading speed were measured using standardized reading texts. Light scatter was quantified with a C-Quant straylight meter and driving reaction times with a computer simulator. Visual clarity of a mobile phone and computer screen was subjectively rated. Distance visual acuity in the 21 volunteers decreased with increasing uncorrected astigmatic power (F = 174.50, P .05); however, the reliability and variability of measurements decreased with increasing uncorrected astigmatic power (P .05), although subjective rating of clarity decreased with increasing uncorrected astigmatic power (P < .001). Uncorrected astigmatism at the 45-degree or 180-degree orientation resulted in worse distance and near visual acuity and subjective-rated clarity than at the 90-degree orientation (P < .05). Uncorrected astigmatism, even as low as 1.00 D, caused significantly decreased vision and if left uncorrected could significantly affect patients' independence, quality of life, and well-being. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.
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            A new method of analyzing vectors for changes in astigmatism.

            N Alpins (1993)
            This method of astigmatism analysis recognizes the need to define an astigmatism goal, thus allowing the surgeon to obtain precise, separate measures of the magnitude and the angle of surgical error. From this, the surgeon can evaluate what surgery may be required to achieve the initial preoperative goal. An index that measures surgical success is adjusted for the level of preoperative astigmatism. The resulting data allow statistical comparison of multiple surgeries and techniques. This method also assists in resolving the case when spectacle and corneal astigmatism do not coincide.
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              Astigmatism analysis by the Alpins method.

              N Alpins (2000)
              To determine the effectiveness of correcting astigmatism by laser refractive surgery by a vectorial astigmatism outcome analysis that uses 3 fundamental vectors: target induced astigmatism vector (TIA), surgically induced astigmatism vector, and difference vector, as described by the Alpins method. A data set of 100 eyes that had laser in situ keratomileusis to correct myopia and astigmatism (minimum preoperative refractive astigmatism 0.75 diopter) was analyzed. The data included preoperative and 3 month postoperative values for manifest refraction and standard keratometry. Using the ASSORT or VectrAK analysis program, individual and aggregate data analyses were performed using simple, polar, and vector analysis of astigmatism and an analysis of spherical change. Statistical analysis of the results was used for means and confidence limits, as well as to examine the differences between corneal and refractive astigmatism outcomes. At an individual patient level, the angle of error was found to be significant, suggesting variable factors at work, such as healing or alignment. A systematic error of undercorrection of astigmatism is prevalent in the treatment of these 100 patients by a factor of between 15% and 30%, depending on whether refractive or corneal values are examined. Spherical correction showed systematic undercorrection of 11%, and parallel indices demonstrated it to be more effective than the astigmatic correction. This method of astigmatism analysis enables the examination of results of astigmatism treatment measured by both refractive and corneal measurements using vector analysis. By examining individual vector relationships to the TIA (ie, the correction index, index of success, and flattening index), a comprehensive astigmatism analysis is completed. Each index provides information necessary for understanding any astigmatic change. Astigmatic outcome parameters are more favorable when measured by subjective refractive than objective corneal methods.

                Author and article information

                BMC Ophthalmol
                BMC Ophthalmol
                BMC Ophthalmology
                BioMed Central
                6 January 2014
                : 14
                : 1
                [1 ]Department of Ophthalmology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg, 20246, Germany
                Copyright © 2014 Katz et al.; licensee BioMed Central Ltd.

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                : 22 July 2013
                : 2 January 2014
                Research Article

                Ophthalmology & Optometry
                low myopia,induced astigmatism,laser in situ keratomileusis,cylinder axis,low astigmatism,alpins vector method


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