A Novel Approach to Enhancement Linked Laser Asymmetric Keratectomy Using Semi-Cylindrical
      Ablation Pattern in Patients with Myopic Regression After Laser Refractive Surgery

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Abstract

Purpose

We aimed to introduce a new technique to reduce regional asymmetry of corneal thickness by assessing its effectiveness in four patients with myopic regression after laser refractive surgery (LRS).

Patients and Methods

Four patients (four eyes) with myopic regression after LRS were included in this study. A new technique of enhancement with laser epithelial keratomileusis-linked laser asymmetric keratectomy using semi-cylindrical ablation pattern (E-LAK-SCAP) with full integration of the Vision-Up software for analyzing the corneal thickness deviation can be used to create central symmetry by blocking laser ablation on the thin cornea. It reduces the regional asymmetry of the corneal thickness, thus improving corneal symmetry and correcting the refractive power and myopic shift due to E-LAK-SCAP. We measured refraction, visual acuity, intraocular pressure (IOP), central corneal thickness (CCT), corneal irregularities in the 3.0mm, and 5.0 zones on Orbscan maps, the sum of corneal thickness deviations in four directions (SUM), distance between the maximum posterior elevation (best-fit-sphere [BFS]) and the visual axis (DISTANCE), and angle kappa before and after LRS and E-LAK-SCAP. Blurring scores were measured before and after E-LAK-SCAP.

Results

The uncorrected far visual acuity (LogMAR) increased after LRS and E-LAK-SCAP. SUM (µm) increased after LRS in three cases, but decreased in all four cases after E-LAK-SCAP. DISTANCE increased after LRS, but decreased after E-LAK-SCAP. The spherical equivalent, CCT, decreased after LRS and E-LAK-SCAP. Blurring scores decreased after E-LAK-SCAP, and angle kappa was similar before and after LRS, but decreased after E-LAK-SCAP. IOP was similar before and after both LRS and E-LAK-SCAP.

Conclusion

E-LAK-SCAP improved corneal symmetry by reducing the SUM and DISTANCE, showing good postoperative visual acuity, and blurring was reduced postoperatively. There was no myopic regression in the one-year postoperative period.

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Most cited references 18

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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): Clin Ophthalmol

Journal ID (iso-abbrev): Clin Ophthalmol

Journal ID (publisher-id): opth

Journal ID (pmc): clinop

Title: Clinical Ophthalmology (Auckland, N.Z.)

Publisher: Dove

ISSN (Print): 1177-5467

ISSN (Electronic): 1177-5483

Publication date (Electronic): 23 April 2021

Publication date Collection: 2021

Volume: 15

Pages: 1751-1758

Affiliations

[1 ]Kim’s Eye Hospital, Division of Cornea, Cataract, and Refractive Surgery, Konyang University School of Medicine , Seoul, South Korea

[2 ]Woori Eye Clinic, Department of Ophthalmology, Yonsei University School of Medicine , Daejon, South Korea

Author notes

Correspondence: Byung Moo Min Woori Eye Clinic, Department of Ophthalmology, Yonsei University School of Medicine , Daeduk Daero 219 (Dunsan-dong), Seo-gu, Daejon, 35229, South KoreaTel +82-42-476-1675Fax +82-42-476-1670 Email bmin8275@naver.com

Article

Publisher ID: 306636

DOI: 10.2147/OPTH.S306636

PMC ID: 8080158

SO-VID: 95f57d6c-2a66-4ce4-b5b2-8d1a742d41a8

License:

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. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

History

Date received : 14 February 2021

Date accepted : 09 April 2021

Page count

Figures: 6, Tables: 6, References: 18, Pages: 8

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A Novel Approach to Enhancement Linked Laser Asymmetric Keratectomy Using Semi-Cylindrical Ablation Pattern in Patients with Myopic Regression After Laser Refractive Surgery

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Abstract

Purpose

Patients and Methods

Results

Conclusion

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Karger: Ophthalmology

Most cited references 18

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

Biomechanics of corneal ectasia and biomechanical treatments.

Influence of corneal biomechanical properties on intraocular pressure measurement: quantitative analysis.

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