• Users Online: 291
  • Print this page
  • Email this page


 
 Table of Contents  
CASE REPORT
Year : 2022  |  Volume : 34  |  Issue : 3  |  Page : 357-363

Corneal Ectasia after Laser-Assisted Small-Incision Lenticule Extraction: The Case for an Enhanced Ectasia Risk Assessment


1 Eye Research Center, Department of Ophthalmology, Mashhad University of Medical Sciences, Mashhad, Iran
2 Refractive Error Research Center, Department of Optometry, Mashhad University of Medical Sciences, Mashhad, Iran
3 Instituto de Olhos Renato Ambrósio/Visare Personal Laser, and Department of Ophthalmology, Federal University of the State of Rio de Janeiro, Rio de Janeiro, Brazil

Date of Submission01-Mar-2022
Date of Decision26-Mar-2022
Date of Acceptance05-Apr-2022
Date of Web Publication30-Nov-2022

Correspondence Address:
Samira Hassanzadeh
Refractive Error Research Center, Department of Optometry, Mashhad University of Medical Sciences, Mashhad
Iran
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/joco.joco_79_22

Rights and Permissions
  Abstract 


Purpose: To present a case of asymmetric progressive corneal ectasia following femtosecond laser-assisted small-incision lenticule extraction.
Methods: After obtaining a patient's consent, preoperative and postoperative findings were represented in this case report.
Results: A 29-year-old woman presented with normal preoperative Placido disk-based corneal topography and tomographic findings. The corrected refractive error was −4.00 and −4.50 −1.00 × 177 in the right and left eye, respectively, with a maximal lenticule thickness of 87 and 115 μm OD/OS. Twenty months postoperatively, the patient presented with decreased vision in the left eye and mild ectatic changes in corneal shape in both eyes. The retrospective evaluation of the integrated rotating Scheimpflug tomography (Pentacam; Oculus, Wetzlar, Germany) and corneal biomechanical (Corvis ST) assessment revealed moderate susceptibility for corneal ectasia in the right eye and a significant corneal ectasia in the left eye.
Conclusion: This case corroborates the need for an enhanced multimodal approach to characterize the risk for postoperative corneal ectasia after laser vision correction.

Keywords: Biomechanics, Corneal ectasia, Small-incision lenticule extraction


How to cite this article:
Zarei-Ghanavati S, Hassanzadeh S, Ambrósio R. Corneal Ectasia after Laser-Assisted Small-Incision Lenticule Extraction: The Case for an Enhanced Ectasia Risk Assessment. J Curr Ophthalmol 2022;34:357-63

How to cite this URL:
Zarei-Ghanavati S, Hassanzadeh S, Ambrósio R. Corneal Ectasia after Laser-Assisted Small-Incision Lenticule Extraction: The Case for an Enhanced Ectasia Risk Assessment. J Curr Ophthalmol [serial online] 2022 [cited 2023 Feb 4];34:357-63. Available from: http://www.jcurrophthalmol.org/text.asp?2022/34/3/357/362465




  Introduction Top


Excellent safety and efficacy have been reported for the small-incision lenticule extraction (SMILE) technique as a flapless procedure.[1] Although the SMILE procedure may theoretically reduce the risk of corneal ectasia, it is not eliminated due to corneal alterations by tissue removal and biomechanical weakening of the cornea.[2],[3] This report describes a case of asymmetric progressive corneal ectasia following femtosecond laser-assisted SMILE.


  Case Report Top


A 29-year-old woman seeking refractive surgery presented in our clinic in 2019. Baseline refractive characteristics are presented in [Table 1]. An informed consent was obtained from the patient. The patient had no ocular disease and no family history of keratoconus. The corrected distance visual acuity (CDVA) was 20/20 in both eyes. A full ophthalmologic assessment and diagnostic imaging including Placido disk-based topography (TMS-4N, Tomey Corp.), tomography using Pentacam HR (Oculus; Wetzlar, Germany), and corneal biomechanical assessment by Corvis ST was performed preoperatively.
Table 1: Preoperative and postoperative characteristics of the patient and small-incision lenticule extraction surgical parameters

Click here to view


Preoperative topography-based keratometry was 45.54 @1°/46.84 @91° diopters (D) in the right eye and 45.75 @3°/47.69 @93°D in the left eye. The cornea in both eyes was steep, but there was no SRAX or significant inferior steepening. The surface asymmetry index was abnormal in the right eye (1.67). No keratoconus pattern was detected by Klyce/Maeda and Smolek/Klyce classifications [Figure 1]. Pentacam imaging showed no significant abnormal finding. The ART-Max was 350/355 μm for OD/OS. In Belin/Ambrósio enhanced ectasia map, the average progression index was borderline in both eyes (1.16 and 1.19 for the right and left eye). As a result, a borderline thickness distribution map and Belin/Ambrósio deviation of 2.02 D in the right eye and 2.09 D in the left eye was found [Figure 2]. In KC/staging map, no abnormal indices were found for both eyes. The thinnest corneal thickness was 513 and 514 μm in the right and left eye. Preoperative anterior/posterior elevation was +3/+11 μm OD and +6/+11 μm OS, which were in the normal range [Figure 2]. In the Corvis biomechanical/tomographic assessment map, four Corvis ST indices (DA ratio, ARTh, stiffness parameter A1, and integrated radius) were borderline and in the overlap zone of the normal–abnormal area in both eyes. The corneal biomechanical index (CBI) was abnormal (more than 0.50) in both eyes. However, the tomographic biomechanical index (TBI) was in the normal range (0.20 in the right eye and 0.33 in the left eye). Furthermore, the Pentacam Random Forest Index was normal in both eyes (0.07 and 0.23) [Figure 3].
Figure 1: Preoperative (top) and 20 months postoperative (bottom) Placido disk-based topography images with keratoconus screening indices. Figure shows normal preoperative topographic findings in both eyes

Click here to view
Figure 2: Preoperative tomography displays of Pentacam HR in the right and left eye do not show significant abnormalities

Click here to view
Figure 3: Preoperative Corvis biomechanical properties of the right and left eye. Figure shows abnormal tomographic biomechanical index and corneal biomechanical index in the left eye

Click here to view


The patient had no other abnormality in terms of review of the system concerning sleep apnea, obesity, eye rubbing habit, allergies, etc., and was considered a low risk, suitable candidate for SMILE procedure using VisuMax femtosecond laser system (Carl Zeiss Meditec AG, Germany). The surgery was uneventful. [Table 1] shows surgical characteristics.

Examinations were normal in 1-week, 1-month, 3-month, and 1-year follow-ups. After 20 months, the patients presented with decreased vision in the left eye (CDVA: 20/30). Imaging revealed corneal ectasia in the left eye and mild ectasia in the right eye. The ART-Max was 169 and 120 μm for the right and left eye, respectively. Post-laser vision correction CBI and the subtraction tomographic maps showed significant ectasia in the left eye [Figure 4], [Figure 5], [Figure 6]. Posterior elevation and best fit sphere 8-mm diameter considered the same reference for post- and preoperative calculation. Postoperative anterior/posterior elevation was +11/+8 μm in the right eye and +13/+25 μm in the left eye.
Figure 4: Postoperative tomography displays abnormal Pentacam parameters in the right and especially left eye

Click here to view
Figure 5: Twenty months postoperatively, Corvis biomechanical properties of the right and left eye

Click here to view
Figure 6: Tomographic subtraction maps of pre/postoperative data shows a significant postoperative corneal ectasia in the left eye

Click here to view


Corneal collagen cross-linking was performed on the left eye to arrest more ectasia progression, and the right eye was followed. The patient's consent was obtained to report her findings as a case representation.


  Discussion Top


Histological studies on the ultrastructure of corneal stroma show that the collagen fibers network is denser in the anterior stroma. This unique geometry is responsible for stiffer biomechanical properties in the anterior part of the cornea.[4] In the SMILE procedure, the lenticule is extracted from within the stroma, and the anterior stroma remains intact. Randleman et al.[3] showed that the posterior 60% of the stroma is 50% weaker than the anterior 40% of the corneal stroma. A mathematical model created by Reinstein et al.[2] derived from depth-dependent stromal tensile strength data. This model theoretically showed that the SMILE procedure might leave the corneal with greater tensile strength than photorefractive keratectomy or laser in situ keratomileusis (LASIK) procedures.

Excellent safety and efficacy have been reported to be achievable with SMILE as a flapless procedure.[5] Although the SMILE procedure may theoretically reduce the risk of corneal ectasia, it is not eliminated due to corneal alterations by tissue removal and biomechanical weakening of the cornea. Postoperative ectasia can be an inherent risk associated with the SMILE technique. Among all SMILE surgeries which have been performed worldwide, a few postoperative ectasia cases have been reported.[1],[6],[7],[8],[9] Although most of these cases occurred in patients with preoperative subclinical keratoconus or with an underlying corneal pathology,[10] rare cases with normal preoperative topography have been reported in the literature.[1],[7] Moshirfar et al.[10] in their review of ectasia cases following the SMILE procedure, stated that abnormal topography might not be the only risk factor for postoperative corneal ectasia progression. They also evaluated four cases of post-SMILE ectasia using calculated percent tissue altered (PTA) as an ectasia risk assessment factor and introduced a modified PTA (mPTA) formula for SMILE cases. According to the traditional formula, the PTA of our patients' right and left eyes was 43.6% and 48.7%, which were more than the cut-off point of 40%. Moshirfar et al.[10] modified the PTA formula based on the weakening effect of SMILE vertical side cuts on the corneal structure and showed inaccuracy of traditional PTA formula for SMILE cases.[10] Based on the mPTA formula, the left eye of our patients was at high risk for SMILE surgery (more than 20%). Nevertheless, based on the PTA and mPTA formulae, increasing cap thickness increases the PTA and the ectasia risk. This is against the theory of saving the stronger anterior cornea by using thicker caps. In other words, in the SMILE procedure, we can change the cap thickness from 110 μm to 140 μm to preserve the biomechanical properties of the anterior cornea without altering the visual outcome.[11],[12],[13],[14] Still, it seems that the PTA formula needs further improvement for expressing the impact of the SMILE procedure, considering the positive effect of increasing cap thickness on corneal biomechanical properties, which is different from flap thickness in LASIK. However, in SMILE surgery, like other refractive surgery techniques, minimizing tissue removal is very important to lessen tissue alterations and lessen postoperative corneal biomechanical changes.

Today, preoperative detection of the mild and subclinical form of corneal ectasia has evolved to the characterization of ectasia susceptibility using a combination of tomographic–biomechanical diagnostic data. However, our case shows that post-SMILE corneal ectasia may happen, despite preoperative normal imaging, low refractive error correction, and considering a flap thickness of 140 μm for preserving anterior stroma. Future studies incorporating artificial intelligence and improving algorithms will detect very mild and susceptible ectasia diseases before refractive surgeries.[15],[16] Furthermore, data from patients with preoperative normal cornea who had corneal ectasia after laser vision correction procedures on the cornea, is helpful for developing more accurate ectasia risk assessment strategies.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
El-Naggar MT. Bilateral ectasia after femtosecond laser-assisted small-incision lenticule extraction. J Cataract Refract Surg 2015;41:884-8.  Back to cited text no. 1
    
2.
Reinstein DZ, Archer TJ, Randleman JB. Mathematical model to compare the relative tensile strength of the cornea after PRK, LASIK, and small incision lenticule extraction. J Refract Surg 2013;29:454-60.  Back to cited text no. 2
    
3.
Randleman JB, Dawson DG, Grossniklaus HE, McCarey BE, Edelhauser HF. Depth-dependent cohesive tensile strength in human donor corneas: Implications for refractive surgery. J Refract Surg 2008;24:S85-9.  Back to cited text no. 3
    
4.
Meek KM, Knupp C. Corneal structure and transparency. Prog Retin Eye Res 2015;49:1-16.  Back to cited text no. 4
    
5.
Randleman JB. Small incision lenticule extraction (SMILE): What now? What next?.Ophthalmology 2020;127:1035-6.  Back to cited text no. 5
    
6.
Gavrilov JC, Atia R, Borderie V, Laroche L, Bouheraoua N. Unilateral corneal ectasia after small-incision lenticule extraction in a 43-year-old patient. J Cataract Refract Surg 2018;44:403-6.  Back to cited text no. 6
    
7.
Sachdev G, Sachdev MS, Sachdev R, Gupta H. Unilateral corneal ectasia following small-incision lenticule extraction. J Cataract Refract Surg 2015;41:2014-8.  Back to cited text no. 7
    
8.
Mattila JS, Holopainen JM. Bilateral ectasia after femtosecond laser-assisted small incision lenticule extraction (SMILE). J Refract Surg 2016;32:497-500.  Back to cited text no. 8
    
9.
Wang Y, Cui C, Li Z, Tao X, Zhang C, Zhang X, et al. Corneal ectasia 6.5 months after small-incision lenticule extraction. J Cataract Refract Surg 2015;41:1100-6.  Back to cited text no. 9
    
10.
Moshirfar M, Albarracin JC, Desautels JD, Birdsong OC, Linn SH, Hoopes PC Sr. Ectasia following small-incision lenticule extraction (SMILE): A review of the literature. Clin Ophthalmol 2017;11:1683-8.  Back to cited text no. 10
    
11.
Wu, Liu C, Li B, Wang D, Fang X. Influence of cap thickness on corneal curvature and corneal biomechanics after SMILE: A prospective, contralateral eye study. J Refract Surg 2020;36:82-8.  Back to cited text no. 11
    
12.
Wu F, Yin H, Yang Y. Contralateral eye comparison between 2 cap thicknesses in small incision lenticule extraction: 110 versus 130 μm. Cornea 2019;38:617-23.  Back to cited text no. 12
    
13.
El-Massry AA, Goweida MB, Shama Ael-S, Elkhawaga MH, Abdalla MF. Contralateral eye comparison between femtosecond small incision intrastromal lenticule extraction at depths of 100 and 160 μm. Cornea 2015;34:1272-5.  Back to cited text no. 13
    
14.
Damgaard IB, Ivarsen A, Hjortdal J. Refractive correction and biomechanical strength following SMILE with a 110- or 160-μm cap thickness, evaluated Ex Vivo by inflation test. Invest Ophthalmol Vis Sci 2018;59:1836-43.  Back to cited text no. 14
    
15.
Ambrósio R Jr., Ramos I, Lopes B, Santhiago MR, Faria-Correia F, Belin M, et al. Ectasia susceptibility before laser vision correction. J Cataract Refract Surg 2015;41:1335-6.  Back to cited text no. 15
    
16.
Ambrósio R, Faria-Correia F, Ramos I, Valbon BF, Lopes B, Jardim D, et al. Enhanced screening for ectasia susceptibility among refractive candidates: The role of corneal tomography and biomechanics. Curr Ophthalmol Rep 2013;1:28-38.  Back to cited text no. 16
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1]



 

Top
 
 
  Search
 
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

 
  In this article
Abstract
Introduction
Case Report
Discussion
References
Article Figures
Article Tables

 Article Access Statistics
    Viewed403    
    Printed8    
    Emailed0    
    PDF Downloaded37    
    Comments [Add]    

Recommend this journal


[TAG2]
[TAG3]
[TAG4]