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      Ectasia risk factors in refractive surgery

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          Abstract

          This review outlines risk factors of post-laser in situ keratomileusis (LASIK) ectasia that can be detected preoperatively and presents a new metric to be considered in the detection of ectasia risk. Relevant factors in refractive surgery screening include the analysis of intrinsic biomechanical properties (information obtained from corneal topography/tomography and patient’s age), as well as the analysis of alterable biomechanical properties (information obtained from the amount of tissue altered by surgery and the remaining load-bearing tissue). Corneal topography patterns of placido disk seem to play a pivotal role as a surrogate of corneal strength, and abnormal corneal topography remains to be the most important identifiable risk factor for ectasia. Information derived from tomography, such as pachymetric and epithelial maps as well as computational strategies, to help in the detection of keratoconus is additional and relevant. High percentage of tissue altered (PTA) is the most robust risk factor for ectasia after LASIK in patients with normal preoperative corneal topography. Compared to specific residual stromal bed (RSB) or central corneal thickness values, percentage of tissue altered likely provides a more individualized measure of biomechanical alteration because it considers the relationship between thickness, tissue altered through ablation and flap creation, and ultimate RSB thickness. Other recognized risk factors include low RSB, thin cornea, and high myopia. Age is also a very important risk factor and still remains as one of the most overlooked ones. A comprehensive screening approach with the Ectasia Risk Score System, which evaluates multiple risk factors simultaneously, is also a helpful tool in the screening strategy.

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          Risk assessment for ectasia after corneal refractive surgery.

          To analyze the epidemiologic features of ectasia after excimer laser corneal refractive surgery, to identify risk factors for its development, and to devise a screening strategy to minimize its occurrence. Retrospective comparative and case-control study. All cases of ectasia after excimer laser corneal refractive surgery published in the English language with adequate information available through December 2005, unpublished cases seeking treatment at the authors' institution from 1998 through 2005, and a contemporaneous control group who underwent uneventful LASIK and experienced a normal postoperative course. Evaluation of preoperative characteristics, including patient age, gender, spherical equivalent refraction, pachymetry, and topographic patterns; perioperative characteristics, including type of surgery performed, flap thickness, ablation depth, and residual stromal bed (RSB) thickness; and postoperative characteristics including time to onset of ectasia. Development of postoperative corneal ectasia. There were 171 ectasia cases, including 158 published cases and 13 unpublished cases evaluated at the authors' institution. Ectasia occurred after LASIK in 164 cases (95.9%) and after photorefractive keratectomy (PRK) in 7 cases (4.1%). Compared with controls, more ectasia cases had abnormal preoperative topographies (35.7% vs. 0%; P<1.0x10(-15)), were significantly younger (34.4 vs. 40.0 years; P<1.0x10(-7)), were more myopic (-8.53 vs. -5.09 diopters; P<1.0x10(-7)), had thinner corneas before surgery (521.0 vs. 546.5 microm; P<1.0x10(-7)), and had less RSB thickness (256.3 vs. 317.3 microm; P<1.0x10(-10)). Based on subgroup logistic regression analysis, abnormal topography was the most significant factor that discriminated cases from controls, followed by RSB thickness, age, and preoperative corneal thickness, in that order. A risk factor stratification scale was created, taking all recognized risk factors into account in a weighted fashion. This model had a specificity of 91% and a sensitivity of 96% in this series. A quantitative method can be used to identify eyes at risk for developing ectasia after LASIK that, if validated, represents a significant improvement over current screening strategies.
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            Risk factors and prognosis for corneal ectasia after LASIK.

            To review cases of corneal ectasia after laser in situ keratomileusis (LASIK), identify preoperative risk factors, and evaluate methods and success rates of visual rehabilitation for these cases. Retrospective nonrandomized comparative trial. Ten eyes from seven patients identified as developing corneal ectasia after LASIK, 33 previously reported ectasia cases, and two control groups with uneventful LASIK and normal postoperative courses: 100 consecutive cases (first control group), and 100 consecutive cases with high myopia (> 8 diopters [D]) preoperatively (second control group). Retrospective review of preoperative and postoperative data for each case compared with that of previously reported cases and cases with uneventful postoperative courses. Preoperative refraction, topographic features, residual stromal bed thickness (RSB), time to the development of ectasia, number of enhancements, final best-corrected visual acuity (BCVA), and method of final correction. Length of follow-up averaged 23.4 months (range, 6-48 months) after LASIK. Mean time to the development of ectasia averaged 16.3 months (range, 1-45 months). Preoperative refraction averaged -8.69 D compared with -5.37 D for the first control group (P = 0.005). Preoperatively, 88% of ectasia cases met criteria for forme fruste keratoconus, compared with 2% of the first control group (P < 0.0000001) and 4% of the second control group (P = 0.0000001). Seven eyes (70%) had RSB <250 microm, as did 16% of eyes in the first control group and 46% of the second control group. The mean RSB for ectasia cases (222.8 microm) was significantly less than that for the first control group (293.6 micro m, P = 0.0004) and the second control group (256.5 microm; P = 0.04). Seven eyes (70%) had enhancements. Only 10% of eyes lost more than one line of BCVA, and all patients eventually achieved corrected vision of 20/30 or better. One case required penetrating keratoplasty (10%), while all others required rigid gas-permeable contact lenses for correction. Significant risk factors for the development of ectasia after LASIK include high myopia, forme fruste keratoconus, and low RSB. All patients had at least one risk factor other than high myopia, and significant differences remained even when controlling for myopia. Multiple enhancements were common among affected cases, but their causative role remains unknown. We did not identify any patients who developed ectasia without recognizable preoperative risk factors.
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              Novel pachymetric parameters based on corneal tomography for diagnosing keratoconus.

              To describe pachymetric progression indices (PPI) of the Pentacam HR (Oculus Optikgeräte GmbH) and the concept of relational thickness, and to test their accuracy for differentiating keratoconic and normal corneas compared with single-point thickness values. One hundred thirteen individual eyes randomly selected from 113 normal patients and 44 eyes of 44 patients with keratoconus were studied using the Pentacam HR by acquiring central corneal thickness (CCT), thinnest point (TP), position of the TP and PPI at minimal (PPI Min) and maximal (PPI Max) meridians, and the average (PPI Ave) of all meridians. Relational thickness parameters were calculated as the ratios of TP and CCT and PPI values. Mann-Whitney U test assessed differences in groups for each variable. Receiver operating characteristic (ROC) curves were calculated for all variables and pairwise comparisons were performed. Statistically significant differences were noted between normal and keratoconic eyes for all parameters (P<.001), except for horizontal position of TP (P=.79). The best parameters, named Ambrósio's Relational Thickness (ART), were ART-Ave (TP/PPI Ave) and ART-Max (TP/PPI Max) with areas under the ROC curves of 0.987 and 0.983, respectively. The best cutoffs were 424 μm and 339 μm for ART-Ave and ART-Max, respectively. Pachymetric progression indices and ART had a greater area under the curve than TP and CCT (P<.001); TP (0.955) had a greater area under the curve than CCT (0.909; P=.002). Tomographic-derived pachymetric parameters were better able to differentiate normal and keratoconic corneas than single-point pachymetric measurements. Further studies are needed to evaluate the role of tomography in identifying early forms of ectasia as well as ectasia risk among LASIK candidates. Copyright 2011, SLACK Incorporated.
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                Author and article information

                Journal
                Clin Ophthalmol
                Clin Ophthalmol
                Clinical Ophthalmology
                Clinical Ophthalmology (Auckland, N.Z.)
                Dove Medical Press
                1177-5467
                1177-5483
                2016
                20 April 2016
                : 10
                : 713-720
                Affiliations
                [1 ]Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil
                [2 ]Ophthalmology Department, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel
                Author notes
                Correspondence: Marcony R Santhiago, Department of Ophthalmology, Instituto Central, Federal University of São Paulo, AV Dr Enéas de Carvalho Aguiar, 255, São Paulo, Brazil, Email marconysanthiago@ 123456hotmail.com
                Article
                opth-10-713
                10.2147/OPTH.S51313
                4844427
                27143849
                7ed17998-d1d4-4f21-8f42-4581f8c4e2b7
                © 2016 Santhiago et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                History
                Categories
                Review

                Ophthalmology & Optometry
                ectasia,risk factor,refractive surgery,pta
                Ophthalmology & Optometry
                ectasia, risk factor, refractive surgery, pta

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