Correlation between apical protrusion in the Scheimflug imaging and Corneal Hysteresis and Corneal Resistance factor by Ocular Response Analyzer, among refractive non-keratoconic Egyptian patients
Keywords:
apical protrusion, ocular response analyzer (ORA), Lasik, ectasiaAbstract
Introduction: Apical protrusion in the central 4-mm ring in the Scheimflug imaging (Pentacam), both for the anterior and posterior floats as well as Corneal Hysteresis and Corneal Resistance Factor by Ocular Response Analyzer (ORA), generally are considered important predictors for post-Lasik ectasia. The aim of this work was to find out if there is a statistically significant correlation between these different predictors and their correlation with the central corneal thickness for refractive non-keratoconic Egyptian patients trying to achieve a better decision and avoiding ectasia.
Methods: This case-control study involved 142 eyes (of 77 patients with various refractive errors) arriving at the refractive surgery unit in the Research Institute of Ophthalmology in Giza (Egypt) in 2014-2015 seeking excimer laser ablation. The flattest, steepest keratometry readings, central corneal thickness as well as the apical protrusion in the central 4-mm ring, both for the anterior and posterior floats, in microns were measured by Scheimflug imaging. The Corneal Hysteresis and Corneal Resistance Factor were measured by the ocular response analyzer. Statistical analysis was performed by SPSS, using the Pearson correlation test.
Results: The spherical refractive error ranged from +7.00 to -13.00 diopters (-3.80 ± 2.89). The central pachymetry ranged from 494 to 634 µm (550.35 ± 32.13). For the central 4-mm ring, the apical protrusion ranged from 0 to +15 µ (6.93 ± 2.99) for the anterior float and from -3 to +20 µ (9.33 ± 4.55) for the posterior float. The Corneal Hysterisis (CH) ranged from 7 to 14.8 mmHg (10.18±1.44), while the Corneal Resistance Factor (CRF) ranged from 7.5 to 14.9 mmHg (10.58 ± 1.67). There was a strong positive correlation between the central corneal thickness and both Corneal Hysteresis (CH: r = 0.56, P ≤ 0.01) and Corneal Resistance Factor (r = 0.46, P ≤ 0.01). A significant correlation (P < 0.05, r = 0.15) existed between apical protrusion in the posterior float and the central corneal thickness. Also, significant negative correlation (P < 0.05, r = -0.12) existed between apical protrusion in the anterior float by pentacam and the Corneal Resistance Factor by ocular response analyzer.
Conclusions: Our finding of a strong positive correlation between both Corneal Hysteresis and Corneal Resistance Factor and the Central corneal thickness being important for biomechanical corneal stability. The findings of this study also support using both machines preoperatively to decrease the risk of post-Lasik ectasia.
References
Yuen LH, Chan WK, Koh J, Mehta JS, Tan DT; Sing Lasik Research Group. A 10-year prospective audit
of LASIK outcomes for myopia in 37,932 eyes at a single institution in Asia. Sing Lasik Research Group.
Ophthalmology. 2010;117(6):1236-44. doi: 10.1016/j.ophtha.2009.10.042, PMid: 20153899
Dawson DG, Randleman JB, Grossniklaus HE, et al. Corneal ectasia after excimer laser keratorefractive
surgery: histopathology, ultrastructure, and pathophysiology. Ophthalmology. 2008;115(12):2181-91. doi:
1016/j.ophtha.2008.06.008, PMid: 18692245
Ambrosio R, Simplifying Ectasia Screening with Pentacam Corneal Tomography. Highlights of
Ophthalmology. 2010; 38(3):12-20.
Charman WN, “The retinal image in the human eye”, in Progress in Retinal Research, Pergamon, Oxford.
Atchison AA, Smith G, Optics of the Human Eye, Butterworth-Heinnemann, Oxford. 2000.
Artal P, Guirao A, “Contribution of corneal and lens to the aberrations of the human eye”, Opt. Lett.
;23:1713-5. doi: 10.1364/OL.23.001713, PMid: 18091893
Guirao A, Artal P, “Corneal wave-aberrations from videokeratography: accuracy and limitations of the
procedure”, J. Opt. Soc. Am. 2000; 17: 955-65. doi: 10.1364/JOSAA.17.000955, PMid: 10850465
Ambrosio R, Alonso RS, Luz A, Coca Velarde LG. Corneal-thickness spatial profile and corneal-volume
distribution: Tomographic indices to detect keratoconus. J Cataract Refract Surg. 2006;32:1851-9. doi:
1016/j.jcrs.2006.06.025, PMid: 17081868
Vejarano LF. Obtaining essential performance with the pentacam system for corneal surgery. Highlights
Ophthalmol. 2010;38(5):16-22.
Ortiz D, Piñero D, Shabayek MH, Arnalich-Montiel F, and Alió JL, “Corneal biomechanical properties in
normal, post-laser in situ keratomileusis, and keratoconic eyes,” Journal of Cataract and Refractive
Surgery.2007;33(8): 1371-5. doi: 10.1016/j.jcrs.2007.04.021, PMid: 17662426
González-Méijome JM, Villa-Collar C, Queirós A, Jorge J, and Parafita MA, “Pilot study on the influence
of corneal biomechanical properties over the short term in response to corneal refractive therapy for
myopia,” Cornea. 2008;27 (4): 421-6. doi: 10.1097/ICO.0b013e318164e49d, PMid: 18434845
Luce DA. Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J
Cataract Refract Surg. 2005;31:156-62. doi: 10.1016/j.jcrs.2004.10.044, PMid: 15721708
Shah S, Laiquzzaman M, Cunliffe I, Mantry S. The use of the Reichert ocular response analyser to establish
the relationship between ocular hysteresis, corneal resistance factor and central corneal thickness in normal
eyes. Cont Lens Anterior Eye 2006;29(5):257-62. doi: 10.1016/j.clae.2006.09.006, PMid: 17085066
Kamiya K, Hagishima M, Fujimura F, Shimizu K. Factors affecting corneal hysteresis in normal eyes.
Graefes Arch Clin Exp Ophthalmol 2008;246(10):1491-4. doi: 10.1007/s00417-008-0864-x, PMid:
Buratto L, Ferrari M. Indications, techniques, results, limits, and complications of laser in situ
keratomileusis. Curr Opin Ophthalmol. 1997;8:59-66. doi: 10.1097/00055735-199708000-00009, PMid:
Binder PS, Lindstrom RL, Stulting RD, et al. Keratoconus and corneal ectasia after LASIK. J Cataract
Refract Surg 2005;21:749-52. doi: 10.1016/j.jcrs.2005.12.002
De Sanctis U, Missolungi A, Mutani B, Richiardi L, Grignolo FM. Reproducibility and repeatability of
central corneal thickness measurement in keratoconus using the rotating Scheimpflug camera and
ultrasound pachymetry. Am J Ophthalmol. 2007;144:712-8. doi: 10.1016/j.ajo.2007.07.021, PMid:
Chen D, Lam AK. Intrasession and intersession repeatability of the Pentacam system on posterior corneal
assessment in the normal human eye. J Cataract Refract Surg. 2007;33:448-54. doi:
1016/j.jcrs.2006.11.008, PMid: 17321396
Detry-Morel M,Jamart J, Hautenauven F and Pourjavan S. Comparison of the corneal biomechanical
properties with the Ocular Response Analyzer® (ORA) in African and Caucasian normal subjects and
patients with glaucoma, Acta Ophthalmologica. 2012:90(2):118-24. doi: 10.1111/j.1755- 3768.2011.02274.x, PMid: 21989354
Zhang L, Wang Y, Xie L, Geng W, Zuo T. The Relationship between Corneal Biomechanics and Corneal
Shape in Normal Myopic Eyes. J Clin Exp Ophthalmol. 2013; 4: 278. doi:10.4172/2155-9570.1000278.
doi: 10.4172/2155-9570.1000278
Ostadimoghaddam H, Sedaghat MR, Hoseini Yazdi SH, Hamed Niyazmand H. The Correlation between
Biomechanical Properties of Normal Cornea with Tomographic Parameters of Pentacam. Iranian Journal of
Ophthalmology 2012;24(1):11-8.
Dupps WJ, Wilson SE. Biomechanics and wound healing in the cornea. Exp Eye Res. 2006; 83: 709-20.
doi: 10.1016/j.exer.2006.03.015, PMid: 16720023, PMCid: PMC2691611
Published
Issue
Section
License
Copyright (c) 2020 knowledge kingdom publishing
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
