To prospectively review current understanding and future trends of screening for keratectasia risk prior refractive laser vision correction (LVC).
Background
Progressive keratectasia is an uncommon but severe complication of LVC. Preoperative ectatic corneal disease is the most important risk factor. Screening for subclinical ectasia relies on proper interpretation of advanced diagnostic technologies, including front surface corneal topography, three-dimensional tomography, and biomechanical assessments.
Summary
Studies involving eyes with normal and stable corneas, compared to eyes with frank ectatic diseases and to eyes with normal topography from patients with very asymmetric ectasia, allow for developing advanced methods and testing its sensitivity. However, the ideal study populations for testing the sensitivity and specificity of ectasia risk assessments are respectively the preoperative of cases that developed ectasia and the ones with stable outcomes after LVC. Young age and low thickness are surrogates of corneal biomechanics, which may be replaced as risk factors by direct measurements. Keratectasia may also occur due to the surgical impact on corneal structure or due to significant trauma postoperatively. Percentage tissue altered higher than 40% is a more sensitive parameter than a fixed value for minimal residual stromal bed of 250 µm. However, the biomechanical impact from surgery is related to the region and number of lamellae that are severed, so that flap thickness and geometry should play a more relevant role, which is in agreement with finite element simulations. Artificial intelligence methods allow for combining parameters, which significantly enhance the accuracy for detecting ectasia risk.
Conclusion
An enhanced screening approach for preventing keratectasia should consider both preoperative patient-related data and procedure-related parameters to individually characterize ectasia susceptibility or predisposition.
Clinical Significance
Keratectasia is an uncommon, however, severe complication of LVC. Although prevention is the best strategy, an individualized enhanced ectasia screening approach for ectasia risk assessment prior to LVC procedures should integrate patient-related (individual ectasia susceptibility) and procedure-related parameters (biomechanical impact).
How to cite this article
Ambrósio Jr R, Belin MW. Enhanced Screening for Ectasia Risk prior to Laser Vision Correction. Int J Kerat Ect Cor Dis 2017;6(1):23-33.
Iatrogenic keratectasia after LASIK in a case of forme fruste keratoconus. J Cataract Refract Surg 1998 Jul;24(7):1007-1009.
Corneal ectasia induced by laser in situ keratomileusis. J Cataract Refract Surg 2001 Nov;27(11):1796-1802.
Corneal ectasia after myopic laser in situ keratomileusis: a long-term study. Clin Ophthalmol 2012;6:1801-1813.
Progressive keratectasia after laser in situ keratomileusis. J Refract Surg 2004 Sep-Oct;20 (Suppl 5):S718-722.
Rate of ectasia and incidence of irregular topography in patients with unidentified preoperative risk factors undergoing femtosecond laser-assisted LASIK. Clin Ophthalmol 2014;8:35-42.
Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology 2003 Feb;110(2):267-275.
Keratoconus and corneal ectasia after LASIK. J Refract Surg 2005 Nov-Dec;21(6):749-752.
Screening for ectasia risk: what are we screening for and how should we screen for it? J Refract Surg 2013 Apr;29(4):230-232.
Corneal ectasia after excimer laser keratorefractive surgery: histopathology, ultrastructure, and pathophysiology. Ophthalmology 2008 Dec;115(12):2181-2191. e1.
Biomechanics and wound healing in the cornea. Exp Eye Res 2006 Oct;83(4):709-720.
Post-LASIK keratectasia triggered by eye rubbing and treated with topography-guided ablation and collagen cross-linking-a case report. Cornea 2012 May;31(5):575-580.
Validation of the ectasia risk score system for preoperative laser in situ keratomileusis screening. Am J Ophthalmol2008 May; 145(5):813-818.
Am J Ophthalmol 2014 Jul;158(1):87-95 e1.
Corneal topographic and pachymetric screening of keratorefractive patients. J Refract Surg 2003 Jan-Feb;19(1):24-29.
Ectasia after refractive surgery. Ophthalmology2008 Oct;115(10):1849; autor reply 1849-1850.
External analysis of the Randleman ectasia risk factor score system: a review of 36 cases of post LASIK ectasia. Clin ExpOphthalmol 2010 May;38(4): 335-340.
Variability of subjective classifications of corneal topography maps from LASIK candidates. J Refract Surg 2013 No;29(11):770-775.
Topographic and tomographic properties of forme fruste keratoconus corneas. Invest ophthalmol Vis Sci 2010 Nov;51(11):5546-5555.
Scheimpflug imaging for keratoconus and ectatic disease. Indian J Ophthalmol 2013 Aug;61(8): 401-406.
Pentacam scheimpflug tomography findings in topographically normal patients and subclinical keratoconus cases. Am J Ophthalmol 2014 Jul;158(1):32-40. e-2.
Evaluation of corneal shape and biomechanics before LASIK. Int Ophthalmol Clin 2011 Spring;51(2):11-38.
Corneal topographic and tomographic analysis of fellow eyes in unilateral keratoconus patients using pentacam. Am J Ophthalmol 2014 Jan;157(1):103-109. e1.
Detection of subclinical keratoconus using an automated decision tree classification. Am J Ophthalmol 2013 Aug;156(2):237-246. e1.
Influence of the reference surface shape for discriminating between normal corneas, subclinical keratoconus, and keratoconus. J Refract Surg 2013 Apr;29(4):274-281.
Global consensus on keratoconus and ectatic diseases. Cornea. 2015 Apr;34(4):359-369.
Optical coherence tomography combined with videokeratography to differentiate mild keratoconus subtypes. J Refract Surg 2014 Feb;30(2):80-87.
Corneal ectasia after LASIK despite low preoperative risk: tomographic and biomechanical findings in the unoperated, stable, fellow eye. J Refract Surg 2010 Nov;26(11): 906-911.
Preoperative topographic characteristics of eyes that developed postoperative LASIK keratectasia. J Refract Surg 2013 Aug;29(8):540-549.
Assessing ectasia susceptibility prior to LASIK: the role of age and residual stromal bed (RSB) in conjunction to Belin-Ambrósio deviation index (BAD-D). Rev Bras Oftalmol 2014 Mar-Apr;73(2):75-80.
Contemporary Treatment Paradigms in Keratoconus. Cornea 2015 Oct;34(Suppl 10): S16-S23.
Corneal epithelial thickness mapping by Fourier-domain optical coherence tomography in normal and keratoconic eyes. Ophthalmology 2012 Dec;119(12):2425-2433.
Stability of LASIK in topographically suspect keratoconus confirmed non-keratoconic by Artemis VHF digital ultrasound epithelial thickness mapping: 1-year follow-up. J Refract Surg 2009 Jul;25(7): 569-577.
Application of high resolution OCT to evaluate irregularity of Bowman's layer in asymmetric keratoconus. J Biophotonics 2016 May;10(5):701-707.
Biomechanics of corneal ectasia and biomechanical treatments. J Cataract Refract Surg 2014 Jun;40(6):991-998.
Brillouin optical microscopy for corneal biomechanics. Invest Ophthalmol Vis Sci 2012 Jan;53(1):185-190.
Detection of Keratoconus with a new biomechanical index. J Refract Surg 2016 Dec;32(12):803-810.
Enhanced combined tomography and biomechanics data for distinguishing forme fruste keratoconus. J Refract Surg. 2016 Jul;32(7):479-494.
An introduction to understanding elevation-based topography: how elevation data are displayed – a review. Clin Exp Ophthalmol 2009 Jan;37(1):14-29.
Long-term stability of the posterior cornea after laser in situ keratomileusis. J Cataract Refract Surg 2007 Aug;33(8):1366-1370.
Detection of ectatic corneal diseases based on pentacam. Z Med Phys 2016 Jun;26(2):136-142.
Unilateral corneal ectasia after laser in situ keratomileusis in a patient with uncomplicated photorefractive keratectomy in the fellow eye. J Cataract Refract Surg 2007 May;33(5): 859-861.
Effects of variation in depth and side cut angulations in LASIK and thin-flap LASIK using a femtosecond laser: a biomechanical study. J Refract Surg 2012 Jun;28(6):419-425.
Patient-specific finite-element simulation of the human cornea: a clinical validation study on cataract surgery. J Biomech 2013 Feb;46(4):751-758.
Mathematical model to compare the relative tensile strength of the cornea after PRK, LASIK, and small incision lenticule extraction. J Refract Surg 2013 Jul;29(7):454-460.
Integration of Scheimpflug based Corneal Tomography and Biomechanical Assessments for Enhancing Ectasia Detection. J Refract Surg 2017.