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Case report

Corneal ectasia 6.5 months after small-incision lenticule extraction

Wang, Yumeng MM; Cui, Chuanbo MD; Li, Zhiwei PhD; Tao, Xiangchen MD; Zhang, Chunxiao MM; Zhang, Xiao MM; Mu, Guoying MD*

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Journal of Cataract & Refractive Surgery: May 2015 - Volume 41 - Issue 5 - p 1100-1106
doi: 10.1016/j.jcrs.2015.04.001
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Abstract

Small-incision lenticule extraction (SMILE, Carl Zeiss Meditec AG) has been widely used in treating myopia since its first application in 2011.1 Small-incision lenticule extraction evolved from refractive lenticule extraction (ReLEx, Carl Zeiss Meditec AG), which is a flapless corneal refractive surgery.2 Small-incision lenticule extraction uses the all-in-one femtosecond laser in a single refractive surgery, which could reduce the cost and duration of surgery. We describe a case of prominent corneal ectasia after small-incision lenticule extraction, which will enhance our understanding of the complications of the procedure. To our knowledge, this is the first report of corneal ectasia after small-incision lenticule extraction or refractive lenticule extraction.

Case report

A 19-year-old man had small-incision lenticule extraction in both eyes on June 2013. The preoperative uncorrected distance visual acuity (UDVA) was 20/100 and 20/80 in the right eye and left eye, respectively. The preoperative refraction was −6.75 −1.00 × 45 and −6.75 −0.75 × 140, respectively, and the corrected distance visual acuity (CDVA) was 20/20 in both eyes. The cornea thickness was 546 μm in the right eye and 542 μm in the left eye. A retrospective diagnosis of forme fruste keratoconus was made based on anterior surface and posterior surface keratometry values (Scheimpflug pachymetry [Pentacam, Oculus Optikgeräte GmbH]) of 41.7/42.4 diopters (D) and −6.0/−6.5 D, respectively, in the right eye and 41.5/43.0 D and −6.2/−6.6 D, respectively, in the left eye before surgery (Figure 1). The intraocular pressure (IOP) performed by automatic noncontact tonometry (NT-2000, Nidek Co., Ltd.) was 12.5 mm Hg in both eyes. The fundus was normal. The patient had no history of pellucid marginal corneal degeneration and no family history of keratoconus or high myopia. No significant increase in myopia within the previous 2 years was reported by the patient.

Figure 1
Figure 1:
Corneal topography 10 days before small-incision lenticule extraction. A: Right eye. B: Left eye.

Small-incision lenticule extraction was performed uneventfully in both eyes using the Visumax femtosecond laser system (Carl Zeiss Meditec AG). The diameter and thickness of the caps were 7.60 mm and 120 μm, respectively, in both eyes, and the diameter of the optical zone was 6.60 mm in both eyes. The maximum and minimum lenticule thicknesses were 137 μm and 15 μm, respectively, in the right eye and 134 μm and 15 μm, respectively, in the left eye (Figure 2). The UDVA increased to 20/16 in both eyes immediately after surgery. At 1 week, the anterior surface keratometry was 37.0/38.2 D and −6.1/−6.6 D in the right eye and the left eye, respectively, and the posterior surface keratometry was 37.0/38.4 D and −6.3/−6.8 D, respectively (Table 1).

Figure 2
Figure 2:
Treatment data of small-incision lenticule extraction.
Table 1
Table 1:
Preoperative and postoperative findings.

At 6.5 months, corneal topography revealed corneal ectasia. The anterior surface keratometry was 38.4/39.5 D in the right eye and 38.6/40.8 D in the left eye, and the posterior surface keratometry was −6.3/−6.8 D and −7.1/−6.6 D, respectively (Table 1 and Figure 3).

Figure 3
Figure 3:
Corneal topography 6.5 months after small-incision lenticule extraction. A: Right eye. B: Left eye.

At 13 months, the UDVA was 20/25 in the right eye and 20/20 in the left eye, a decrease from the UDVA at 1 week. The refraction was −3.25 −1.50 × 41 and −4.50 −1.25 × 132, respectively. The corneal thickness at the thinnest point using Scheimpflug pachymetry was 423 μm and 414 μm in the right eye and left eye, respectively, with inferior topographic steepening in both eyes. The anterior surface keratometry was 39.8/42.0 D and 42.2/44.3 D, respectively, and the posterior surface keratometry was −7.2/−6.5 D and −7.1/−6.6 D, respectively (Figure 4). The IOP by automatic noncontact tonometry was 8.0 mm Hg in both eyes. A forward protrusion of the cornea was observed at the slitlamp.

Figure 4
Figure 4:
Corneal topography 13 months after small-incision lenticule extraction. A: Right eye. B: Left eye.

Discussion

To our knowledge, this is the first report of a patient with corneal ectasia after small-incision lenticule extraction. Various complications that do not threaten visual acuity have been reported after small-incision lenticule extraction; ie, dry eye,3,4 tear-film instability,4 decrease in corneal sensitivity,4 loss of CDVA,5 and undercorrection of the astigmatic error.6 Patients with forme fruste keratoconus,7 keratoconus,8 and high myopia7,9 have developed corneal ectasia after laser in situ keratomileusis (LASIK), and some patients without preoperative risk factors have also developed corneal ectasia after LASIK.10,11 However, there have been no reports of corneal ectasia after small-incision lenticule extraction.

The anterior lamellae remain more intact after small-incision lenticule extraction than after photorefractive keratectomy (PRK) or LASIK, and the total stromal tensile strength is relatively higher after small-incision lenticule extraction,12 which results in less nerve damage and faster nerve recovery than LASIK or PRK.13 In LASIK, the ablation of stroma leads to the deregulation of keratocyte apoptosis, which in turn leads to changes in proteolysis and wound-healing dynamics.14 Small-incision lenticule extraction induces less of a decrease in subbasal nerve fiber density and less keratocyte apoptosis, proliferation, and inflammation than femtosecond laser–assisted LASIK.15 Although the pathologic changes are less severe after small-incision lenticule extraction than after LASIK or femtosecond laser–assisted LASIK, corneal hysteresis and the corneal resistance factor decrease after small-incision lenticule extraction16 and a significant change in corneal deformation parameters has been observed.17 Previous reports highlight the possibility of biomechanical changes in the cornea after small-incision lenticule extraction and suggest a possible mechanism underlying the result observed in the present case.

The retrospective diagnosis of forme fruste keratoconus in our case was made because the preoperative pachymetry examination showed a decentered elevation coincident with the thinnest point on the posterior surface and a slight asymmetry on the anterior surface. The increase in the keratometry value after small-incision lenticule extraction emphasizes the importance of a thorough preoperative pachymetry analysis. The relationship between epithelial thickness and posterior surface elevation should be considered as the epithelial thinning over the cone will mask the cone from anterior surface topography. In early keratoconus, the front surface of corneal topography can appear completely normal, leading to an incorrect diagnosis.

Our report indicates that ectasia can occur after small-incision lenticule extraction in patients with forme fruste keratoconus, highlighting the importance of stricter regulation of patient recruitment before the procedure and postoperative follow-up. The same safety regulations used for LASIK should be applied to small-incision lenticule extraction to prevent the occurrence of postoperative ectasia. We also recommend obtaining more patient information, including corneal biomechanical properties, to ensure a good outcome after small-incision lenticule extraction.

References

1. Sekundo W, Kunert KS, Blum M. Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study. Br J Ophthalmol. 2011;95:335-339.
2. Ang M, Tan D, Mehta JS. Small incision lenticule extraction (SMILE) versus laser in-situ keratomileusis (LASIK): study protocol for a randomized, non-inferiority trial. Trials. 13, 2012, 75, Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3404906/pdf/1745-6215-13-75.pdf. Accessed January 31, 2015.
3. Xu Y, Yang Y. Dry eye after small incision lenticule extraction and LASIK for myopia. J Refract Surg. 2014;30:186-190.
4. Li M, Zhao J, Shen Y, Li T, He L, Xu H, Yu Y, Zhou X. Comparison of dry eye and corneal sensitivity between small incision lenticule extraction and femtosecond LASIK for myopia. PLoS One. 8(10): 2013, e77797, Available at: http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0077797&representation=PDF. Accessed January 31, 2015.
5. Ivarsen A, Asp S, Hjortdal J. Safety and complications of more than 1500 small-incision lenticule extraction procedures. Ophthalmology. 2014;121:822-828.
6. Ivarsen A, Hjortdal J. Correction of myopic astigmatism with small incision lenticule extraction. J Refract Surg. 2014;30:240-247.
7. Randleman JB, Russell B, Ward MA, Thompson KP, Stulting RD. Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology. 2003;110:267-275.
8. Schmitt-Bernard C.-F.M, Lesage C, Arnaud B. Keratectasia induced by laser in situ keratomileusis in keratoconus. J Refract Surg. 2000;16:368-370.
9. Joo C-K, Kim T-G. Corneal ectasia detected after laser in situ keratomileusis for correction of less than −12 diopters of myopia. J Cataract Refract Surg. 2000;26:292-295.
10. Amoils SP, Deist MB, Gous P, Amoils PM. Iatrogenic keratectasia after laser in situ keratomileusis for less than −4.0 to −7.0 diopters of myopia. J Cataract Refract Surg. 2000;26:967-977.
11. Geggel HS, Talley AR. Delayed onset keratectasia following laser in situ keratomileusis. J Cataract Refract Surg. 1999;25:582-586.
12. 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. 29, 2013, p. 454-460, Available at: http://www.choeye.co.kr/webi_board/upFile/mathematical_model_to_compare_the_reletive_tensile_strength_of_the_cornea_after_PRK_Lasik_Smile.pdf. Accessed January 31, 2015.
13. Mohamed-Noriega K, Riau AK, Lwin NC, Chaurasia SS, Tan DT, Mehta JS. Early corneal nerve damage and recovery following small incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK). Invest Ophthalmol Vis Sci. 55, 2014, p. 1823-1834, Available at: http://www.iovs.org/content/55/3/1823.full.pdf. Accessed January 31, 2015.
14. Ou RJ, Shaw EL, Glasgow BJ. Keratectasia after laser in situ keratomileusis (LASIK): evaluation of the calculated residual stromal bed thickness. Am J Ophthalmol. 2002;134:771-773.
15. Dong Z, Zhou X, Wu J, Zhang Z, Li T, Zhou Z, Zhang S, Li G. Small incision lenticule extraction (SMILE) and femtosecond laser LASIK: Comparison of corneal wound healing and inflammation. Br J Ophthalmol. 98, 2014, p. 263-269, Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3913294/pdf/bjophthalmol-2013-303415.pdf. Accessed January 31, 2015.
16. Agca A, Ozgurhan EB, Demirok A, Bozkurt E, Celik U, Ozkaya A, Cankaya I, Yilmaz OF. Comparison of corneal hysteresis and corneal resistance factor after small incision lenticule extraction and femtosecond laser-assisted LASIK: a prospective fellow eye study. Cont Lens Anterior Eye. 2014;37:77-80.
17. Shen Y, Zhao J, Yao P, Miao H, Niu L, Wang X, Zhou X. Changes in corneal deformation parameters after lenticule creation and extraction during small incision lenticule extraction (SMILE) procedure. PLoS One. 9(8): 2014, e103893, Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4133203/pdf/pone.0103893.pdf. Accessed January 31, 2015.
© 2015 by Lippincott Williams & Wilkins, Inc.