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      Comparison of outcomes of laser refractive surgery (LRS) alone and LRS with laser asymmetric keratectomy in patients with myopia : A retrospective study

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      Author(s): , MD, PhD a , , MD, PhD b , ∗
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      Publication date (Electronic):
      Journal: Medicine
      Publisher: Lippincott Williams & Wilkins
      Keywords: laser asymmetric keratectomy, laser refractive surgery, myopia

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          Abstract

          To compare and analyze the postoperative 1-year outcomes of laser refractive surgery (LRS) alone vs LRS with laser asymmetric keratectomy (LAK), in patients with myopia, for preventing and resolving LRS complications.

          This retrospective study compared the preoperative and 1-year postoperative outcomes between the control and comparison groups using a sum of deviations in corneal thickness in 4 directions >80 μm. The control group included 41 patients with myopia (41 eyes) who underwent LRS. The comparison group included 33 patients (33 eyes) who received LAK-linked LRS. Age, spherical equivalent (SE), sphere, cylinder, uncorrected distance visual acuity (UDVA), pupil size, kappa angle, central corneal thickness, corneal irregularity in the 3.0 mm zone on Orbscan maps (SUM), distance between the maximum posterior elevation (best-fit-sphere) and the visual axis (DISTANCE), postoperative blurring scores, frequency of postoperative myopic regression, and efficiency index were compared.

          Preoperative age ( P = .198), SE ( P = .686), sphere ( P = .562), cylinder ( P = .883), UDVA ( P = .139), pupil size ( P = .162), kappa angle ( P = .807), central corneal thickness ( P = .738), corneal irregularity ( P = .826), SUM ( P = .774), and DISTANCE ( P = .716) were similar between the 2 groups. The 1-year postoperative SE ( P = .024), sphere ( P = .022), corneal irregularity ( P = .033), SUM ( P = .000), DISTANCE ( P = .04), blurring scores ( P = .000), and frequency of postoperative myopic regression ( P = .004) were significantly decreased in the comparison group compared to the control group. UDVA ( P = .014) and the efficiency index ( P = .035) were higher in the comparison group.

          LAK with LRS improved corneal symmetry by reducing the SUM and DISTANCE. UDVA and efficiency index were also improved and blurring and myopic regression were reduced postoperatively.

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          Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes.

          Dolores Ortiz, David Piñero, Mohamed Shabayek … (2007)
          To compare the biomechanical properties of normal, post-laser in situ keratomileusis (LASIK), and keratoconic corneas evaluated by corneal hysteresis and the corneal resistance factor measured with the Reichert Ocular Response Analyzer (ORA). Instituto Oftalmológico de Alicante, Vissum, Alicante, Spain. Two hundred fifty eyes were divided into 3 groups: normal (control group), post-LASIK, and keratoconus. The corneal biomechanical properties were measured with the ORA, which uses a dynamic bidirectional applanation process. The main outcome measures were intraocular pressure, corneal hysteresis, and the corneal resistance factor. The control group had 165 eyes; the LASIK group, 65 eyes; and the keratoconus group, 21 eyes. In the control group, the mean corneal hysteresis value was 10.8 mm Hg +/- 1.5 (SD) and the mean corneal resistance factor, 11.0 +/- 1.6 mm Hg. The corneal hysteresis value was lower in older eyes, and the difference between the youngest age group (9 to 14 years) and oldest age group (60 to 80 years) was statistically significant (P = .01, t test). One month after LASIK, corneal hysteresis and the corneal resistance factor decreased significantly, from 10.44 to 9.3 mm Hg and from 10.07 to 8.13 mm Hg, respectively. In the keratoconus group, the mean corneal hysteresis was 7.5 +/- 1.2 mm Hg and the mean corneal resistance factor, 6.2 +/- 1.9 mm Hg. There were statistically significant differences in both biomechanical parameters between keratoconic eyes and post-LASIK eyes (P<.001, t test). The corneal hysteresis and corneal resistance factor values were significantly lower in keratoconic eyes than in post-LASIK eyes. Future work is needed to determine whether these differences are useful in detecting keratoconus when other diagnostic tests are equivocal.
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            Biomechanics of corneal ectasia and biomechanical treatments.

            Cynthia Roberts, William J Dupps (2014)
            Many algorithms exist for the topographic/tomographic detection of corneas at risk for post-refractive surgery ectasia. It is proposed that the reason for the difficulty in finding a universal screening tool based on corneal morphologic features is that curvature, elevation, and pachymetric changes are all secondary signs of keratoconus and post-refractive surgery ectasia and that the primary abnormality is in the biomechanical properties. It is further proposed that the biomechanical modification is focal in nature, rather than a uniform generalized weakening, and that the focal reduction in elastic modulus precipitates a cycle of biomechanical decompensation that is driven by asymmetry in the biomechanical properties. This initiates a repeating cycle of increased strain, stress redistribution, and subsequent focal steepening and thinning. Various interventions are described in terms of how this cycle of biomechanical decompensation is interrupted, such as intrastromal corneal ring segments, which redistribute the corneal stress, and collagen crosslinking, which modifies the basic structural properties.
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              Influence of corneal biomechanical properties on intraocular pressure measurement: quantitative analysis.

              Fu-Jun Liu, J. Roberts (2004)
              To understand and quantify intraocular pressure (IOP) measurement errors introduced by corneal variables during applanation tonometry using a cornea biomechanical model. Department of Ophthalmology, Biomedical Engineering Center, The Ohio State University, Columbus, Ohio, USA. The model assumed an overall resultant pressure that was based on the summation of the applanation pressure, the true IOP, and the surface tension caused by the tear film to determine the final deformation of the corneal apex during IOP measurement. Corneal resistance was varied according to the cornea's biomechanical properties, thickness, and curvature, and the effect of each variable on the accuracy of IOP tonometry readings was examined quantitatively. The model demonstrated that tonometry readings do not always reflect true IOP values. They deviate when corneal thickness, curvature, or biomechanical properties vary from normal values. Based on the model, predicted IOP readings have a 2.87 mm Hg range resulting from the variation in the corneal thickness in the normal population and a 1.76 mm Hg range from the variation in the corneal radius of curvature. Considering that Young's modulus of the corneal varies from 0.1 to 0.9 MPa in the normal population, the model predicts tonometry IOP readings will have a range of 17.26 mm Hg because of the variation in this corneal biomechanical parameter alone. The simulation based on the model demonstrated quantitatively that variations in each corneal variable cause errors in tonometry IOP readings. The simulation results indicate that differences in corneal biomechanics across individuals may have greater impact on IOP measurement errors than corneal thickness or curvature.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Medicine (Baltimore)
                Journal ID (iso-abbrev): Medicine (Baltimore)
                Journal ID (publisher-id): MEDI
                Title: Medicine
                Publisher: Lippincott Williams & Wilkins (Hagerstown, MD )
                ISSN (Print): 0025-7974
                ISSN (Electronic): 1536-5964
                Publication date Collection: 09 April 2021
                Publication date (Electronic): 09 April 2021
                Volume: 100
                Issue: 14
                Electronic Location Identifier: e25366
                Affiliations
                [a ]Kim's Eye Hospital, Division of Cornea,Cataract, and Refractive Surgery. Konyang University School of Medicine. Youngdeungpo-gu, Seoul
                [b ]Woori Eye Clinic, Seo-Ku Daejon, Republic of Korea.
                Author notes
                [∗ ]Correspondence: Byung Moo Min, Woori Eye Clinic, Affiliated Clinical Professor, Department of Ophthalmology, Yonsei University School of Medicine, 219 DaedukDae-Ro (Dunsan dong), Seo-Ku Daejon, 35229, Republic of Korea (e-mail: bmin8275@ 123456naver.com ).
                Author information
                http://orcid.org/0000-0003-1134-8945
                Article
                Publisher ID: MD-D-20-05356 Accession ID: 25366
                DOI: 10.1097/MD.0000000000025366
                PMC ID: 8036046
                PubMed ID: 33832118
                SO-VID: 062cc45b-378c-4153-8637-3d3e7b81624a
                Copyright © Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.
                License:

                This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial License 4.0 (CCBY-NC), where it is permissible to download, share, remix, transform, and buildup the work provided it is properly cited. The work cannot be used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc/4.0

                History
                Date received : 10 June 2020
                Date revision received : 2 February 2021
                Date accepted : 11 March 2021
                Categories
                Subject: 3700
                Subject: Research Article
                Subject: Quality Improvement Study
                Custom metadata
                OPEN-ACCESS TRUE

                Keywords: laser asymmetric keratectomy,laser refractive surgery,myopia
                Data availability:
                Keywords: laser asymmetric keratectomy, laser refractive surgery, myopia

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