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      Posterior Corneal Curvature Assessment after Epi-LASIK for Myopia: Comparison of Orbscan II and Pentacam Imaging

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          Abstract

          Purpose

          To compare the changes in posterior corneal curvature using scanning slit topography (Orbscan II) and Scheimpflug imaging (Pentacam) before and after Epi-laser in situ keratomileusis (LASIK) for myopia.

          Methods

          In a prospective observational case-series study, 20 myopic patients having undergone Epi-LASIK were examined serially with two different devices, Orbscan II and Pentacam, preoperatively and one month postoperatively. Posterior central elevation (PCE) and posterior maximal elevation (PME) were compared between the two devices, and the changes in parameters after Epi-LASIK were analyzed using a difference map.

          Results

          All parameters (preoperative and postoperative PCE and preoperative and postoperative PME) that were measured using the Orbscan II were significantly greater compared to those of the Pentacam (for all p < 0.001). PCE and PME were significantly increased one month postoperatively in the Orbscan II measurements ( p < 0.05) but were not significantly increased in the Pentacam measurements. Also, ΔPCE and ΔPME, in the difference map obtained by each serial scanning, were significantly greater in the Orbscan II measurements than with the Pentacam ( p = 0.012, p = 0.016).

          Conclusions

          The Pentacam measurements displayed significantly reduced values in all parameters related to posterior corneal elevation compared to those of the Orbscan II. The Pentacam showed no significant change in posterior corneal curvature after Epi-LASIK, based on the difference map.

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          Most cited references20

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          Changes in the posterior cornea after laser in situ keratomileusis and photorefractive keratectomy.

          M W Belin, Joseph Ciolino (2006)
          To study the changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) using Scheimpflug topography with the Pentacam anterior segment imaging system (Oculus, Inc.). Department of Ophthalmology, Albany Medical Center, and a private clinical practice, Albany, New York, USA. In this prospective study, 121 consecutive myopic eyes (103 LASIK and 18 PRK) were evaluated preoperatively and postoperatively with the Pentacam to determine elevation changes in the posterior corneal surface. Changes in posterior elevation were calculated by comparing the best-fit sphere preoperatively and postoperatively to a fixed reference sphere using the central 9.0 mm preoperative cornea. Statistical and graphic analyses were performed. The 103 LASIK eyes had a mean correction of -3.76 diopters (D) and a mean ablation depth of 62.1 microm. The mean estimated residual bed thickness (RBT) (329 microm) demonstrated a mean posterior displacement of 2.64 +/- 4.95 microm. The 18 PRK eyes had a mean correction of -2.69 D and a mean ablation depth of 53.2 microm. The mean estimated RBT (464 microm) had a mean posterior displacement of -0.88 +/- 4.64 microm. The difference in the mean posterior corneal displacement between the LASIK and the PRK eyes was not statistically significant (P>.05, Student t test). There was no statistically significant difference in posterior corneal displacement between the LASIK and PRK patients. The changes in PRK and LASIK eyes appeared to be within acceptable measurement variation. Contrary to previous reports, ectatic changes to the posterior corneal surface did not routinely occur after LASIK surgery.
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            Posterior corneal surface topographic changes after laser in situ keratomileusis are related to residual corneal bed thickness.

            Burton Yang, Dian-Jiun Chen, Zhao Wang (1999)
            To determine whether ectasia after laser in situ keratomileusis (LASIK) is related to residual corneal bed thickness. Retrospective noncomparative case series. Thirty-two eyes of 16 patients with refractive errors of -4.00 to -18.00 diopters were examined. LASIK was performed. The topography of the posterior corneal surface was examined with the Orbscan slit scanning corneal topography/pachymetry system. The difference in the elevation of posterior corneal surface regarding the best-fit sphere was measured. After surgery, mean bulge of 17.2 +/- 7.2 microns was found in eyes with residual corneal bed of 250 microns or greater, whereas 41.0 +/- 22.1 microns was seen in eyes with bed thickness less than 250 microns (t = 4.29; P = 0.000). Posterior corneal bulge is correlated with the residual corneal bed thickness. The risk of ectasia may be increased if the residual corneal bed is thinner than 250 microns.
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              Orbscan computerized topography: attributes, applications, and limitations.

              Charles N J McGhee, Gerard Cairns (2004)
              An extensive electronic search was undertaken in January 2004 to identify all relevant peer-reviewed publications on Orbscan slit-scanning/Placido computerized topography. Ninety-one publications were identified. These address elevation topography and best-fit sphere, accuracy and repeatability of anterior and posterior corneal elevation and keratometric maps, comparison of Orbscan-acquired data and Placido-based computerized videokeratography instruments, pachymetry measurement and correlation with ultrasound, screening eye-bank corneas, detection of keratoconus, identifying corneal ectasia after refractive surgery, and miscellaneous applications. Studies were analyzed and critically compared in relation to attributes, applications, and limitations of Orbscan corneal topography. The review highlights advantages of this technique in assessing the cornea in health and disease and after surgery and identifies specific aspects that require further investigation and clarification.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Korean J Ophthalmol
                Journal ID (publisher-id): KJO
                Title: Korean Journal of Ophthalmology : KJO
                Publisher: The Korean Ophthalmological Society
                ISSN (Print): 1011-8942
                ISSN (Electronic): 2092-9382
                Publication date (Print): February 2012
                Publication date (Electronic): 14 January 2012
                Volume: 26
                Issue: 1
                Pages: 6-9
                Affiliations
                [1 ]Department of Ophthalmology and Visual Science, Seoul St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea.
                [2 ]Catholic Institute for Visual Science, The Catholic University of Korea College of Medicine, Seoul, Korea.
                Author notes
                Corresponding Author: Choun-Ki Joo, MD, PhD. Department of Ophthalmology and Visual Science, Seoul St. Mary's Hospital, The Catholic University of Korea College of Medicine, #505 Banpo-dong, Seocho-gu, Seoul 137-701, Korea. Tel: 82-2-2258-1188, Fax: 82-2-599-7405, ckjoo@ 123456catholic.ac.kr
                Article
                DOI: 10.3341/kjo.2012.26.1.6
                PMC ID: 3268172
                PubMed ID: 22323878
                SO-VID: 31b0ff0b-4ec1-4c64-8a4c-87e661befb83
                Copyright © © 2012 The Korean Ophthalmological Society
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 14 January 2010
                Date accepted : 20 December 2010
                Categories
                Subject: Original Article

                ScienceOpen disciplines: Ophthalmology & Optometry
                Keywords: epi-laser in situ keratomileusis,orbscan ii,pentacam,posterior maximal elevation,posterior central elevation
                Data availability:
                ScienceOpen disciplines: Ophthalmology & Optometry
                Keywords: epi-laser in situ keratomileusis, orbscan ii, pentacam, posterior maximal elevation, posterior central elevation

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