Both modalities of refractive lenticule extraction—femtosecond lenticule extraction and small incision lenticule extraction (SMILE)—are considered safe, predictable, and effective in treating myopia and myopic astigmatism.1,2 Nevertheless, the presence of residual refractive errors may require further enhancements.3 Currently, photorefractive keratectomy, LASIK in cap, and Circle are the alternatives for re-treatment after SMILE. To our knowledge, this is the first detailed description of a re-treatment performed with the modified SMILE technique, called sub-cap-lenticule-extraction (SubCap-LE), after a primary SMILE surgery. The aim of this new technique is to leave the cap of the primary SMILE procedure untouched to conserve the benefits associated with SMILE.
A 53-year-old woman presented at our clinic for refractive laser correction. Her preoperative refraction was −6.50 −0.25 × 30° in the right eye and −7.0 −0.25 × 10° in the left eye. The corrected distance visual acuity was 20/20 in both eyes. The central corneal thickness was 543 and 548 µm in the right and left eyes, respectively (OCT/RTvue premier; Optovue, Fremont, CA). Mean keratometry was 44.17 and 44.38 diopters (D) in the right and left eyes, respectively (OPD Scan II; Nidek Co. Ltd, Gamagori, Japan). Mean epithelial thickness was 55 ± 1.9 µm (range: 53 to 60 µm) and topographically regular within the central 5-mm zone in both eyes (OCT/RTvue premier). The SMILE technique using monovision was considered the best surgical option for the primary treatment. The right eye was found to be the dominant eye for distance vision.
The surgical procedure was performed using the VisuMax 500-kHz femtosecond platform (Carl Zeiss Meditec, Jena, Germany). The preoperative planning included an intended lenticule thickness of 137 µm for the right eye and 118 µm for the left eye. A cap thickness of 130 µm, a cap diameter of 7.60 mm, a minimum lenticule thickness of 15 µm, a lenticule diameter of 6.80 mm, and a transition zone of 0.10 mm were used for both eyes. The refractive laser setting included a refraction of −6.75 −0.25 × 30° with a postoperative target of plano in the right eye and −5.50 −0.25 × 10° in the left eye with a targeted refraction of −1.50 D.
Three months after surgery, the patient complained of blurred distance vision. Uncorrected distance visual acuity was 20/63 in the right eye and 20/125 in the left eye. Manifest refraction was −1.00 −1.00 × 5° with a corrected distance visual acuity of 20/20 in the right eye and −1.50 −0.50 × 14° with a corrected distance visual acuity of 20/20 in the left eye. Epithelial integrity reassessment showed a mean thickness of 57 ± 1.7 µm (range: 53 to 61 µm) and a topographically regular distribution within the central 5-mm zone in the right eye. Corneal topography revealed a normal image after SMILE (Figure 1). Total root mean square resulted in 1.49 µm, specifically in 0.47 µm of comatic aberration for a pupil diameter of 6 mm.
Anterior surface corneal topography 3 months after the primary procedure with small incision lenticule extraction (SMILE) technique (above), anterior surface corneal topography 3 months after the secondary procedure with the sub-cap-lenticule-extraction (SubCap-LE) technique (below), and map differential (right).
The patient underwent an enhancement using the SubCap-LE procedure in the right eye using the same laser platform as in the previous procedure. The refractive laser setting was −1.50 −1.25 × 5°, with an intended lenticule thickness of 59 µm, a minimum lenticule thickness of 15 µm, a programmed lenticule diameter of 6.5 mm, and a transition zone of 0.10 mm to increase the space between the new side cut and the incision. The interface of the primary SMILE procedure became the superior plane of the new lenticule and the laser cut the inferior plane and the side cut of the new lenticule (Figure 2B). The surgeon stopped the treatment after the laser cut the new lenticule and the side cut. The new lenticule was removed through the original corneal incision.
Incision planes created in the (A) small incision lenticule extraction (SMILE) procedure and creation of a new lenticule cut and a new lenticule side cut in the (B) sub-cap-lenticule-extraction (SubCap-LE) procedure.
Three months after re-treatment, uncorrected distance visual acuity was 20/16 and the manifest refraction was +0.25 −0.25 × 155° with a corrected distance visual acuity of 20/16. Epithelial thickness was 59 ± 2.1 µm (range: 55 to 64 µm) and it was topographically regular within the central 5-mm zone. The root mean square was 0.46 µm for a pupil of 6-mm diameter, with a coma value of 0.29 µm. The topographic pattern was regular (Figure 1).
The possibility of re-treatment after refractive surgery is significant and depends on several factors, such as preoperative ammetropia, topographical and biomechanical characteristics, individual healing, and patient complaints.4 Successful enhancement of femtosecond lenticule extraction has also been reported.5 A surface ablation is considered the simplest procedure to correct a residual refraction after SMILE, but pain, slow recovery, and postoperative haze are the major concerns.6 Recently, a new strategy called Circle has been developed with the aim of transforming the original cap into a flap.7 It is also possible to perform a secondary SMILE procedure after a primary SMILE procedure; this has the advantage of retaining SMILE’s main benefits, such as absence of pain and dryness and maintenance of biomechanical properties of the cornea.8 However, the challenge is to avoid any interference between the new lenticule and the existing interface. This should be possible by performing the second SMILE either above or below the existing interface. If the primary cap was thick enough, then thin-flap LASIK can be performed. Reinstein et al. showed that the maximum thickness of the epithelium after primary myopic SMILE is 80 µm.9 This means that a re-treatment with a thin flap of 100 µm would not cross either the existing cap interface or into the epithelium, creating a cryptic button hole.
We have described a new method that has the advantage of avoiding interference with the original interface. In contrast to the classic SMILE procedure (Figure 2A), SubCap-LE has no new superior lenticule cut to avoid the risk of a multiple dissection plane. The epithelium gets thicker after myopic LASIK, with maximum thickening centrally and progressively less thickening centrifugally.9 If the epithelium modifications after SMILE are the same as after LASIK, we could expect an undercorrection after SubCap-LE. The changes in epithelial thickness after SMILE need to be studied. In our case, the preoperative and 3-month postoperative epithelial thickness were not clinically different. However, we choose to correct more myopia because we have noted an undercorrection for a few cases in our experience and in the literature.10 In this case, we preferred to risk an overcorrection rather than an undercorrection. But the epithelial thickness variation is an important factor to take into account for the next procedures. To set up the procedure, it is advisable to measure the depth of the primary SMILE interface and the epithelial thickness using high-resolution optical coherence tomography or high-frequency ultrasound devices. A further long-term study is necessary to confirm our preliminary findings.
SubCap-LE enhancement after a primary SMILE procedure to eliminate residual refractive myopic error is feasible and has demonstrated its efficacy and safety in our case. More cases are needed and further studies should be performed to determine a precise surgical profile for SMILE enhancements.
- Vestergaard A, Ivarsen AR, Asp S, Hjortdal JØ. Small-incision lenticule extraction for moderate to high myopia: predictability, safety, and patient satisfaction. J Cataract Refract Surg. 2012;38:2003–2010. doi:10.1016/j.jcrs.2012.07.021 [CrossRef]
- Sekundo W, Gertnere J, Bertelmann T, Solomatin I. One-year refractive results, contrast sensitivity, higher-order aberrations and complications after myopic small-incision lenticule extraction. Graefes Arch Clin Exp Ophthalmol. 2014;252:837–843. doi:10.1007/s00417-014-2608-4 [CrossRef]
- Reinstein D, Archer TJ, Gobbe M. Small incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomes. Eye and Vision. 2014;1(3):1–12. doi:10.1186/s40662-014-0003-1 [CrossRef]
- Parikh NB. Management of residual refractive error after laser in situ keratomileusis and photorefractive keratectomy. Curr Opin Ophthalmol. 2014;25:275–280. doi:10.1097/ICU.0000000000000059 [CrossRef]
- Zhao J, Yao P, Chen Z, Li M, et al. Enhancement of femtosecond lenticule extraction for visual symptomatic eye after myopia correction. BMC Ophthalmol. 2014;14:68. doi:10.1186/1471-2415-14-68 [CrossRef]
- Ivarsen A. Topography-guided photorefractive keratectomy for irregular astigmatism after small incision lenticule extraction. J Refract Surg. 2014;30:429–432. doi:10.3928/1081597X-20140508-02 [CrossRef]
- Riau A, Ang H, Lwin N, Chaurasia S, Tan D, Mehta J. Comparison of four different VisuMax Circle patterns for flap creation after small incision lenticule extraction. J Refract Surg. 2013;29:236–244. doi:10.3928/1081597X-20130318-02 [CrossRef]
- Sinha Roy A, Dupps WJ Jr, Roberts CJ. Comparison of biomechanical effects of small-incision lenticule extraction and laser in situ keratomileusis: finite-element analysis. J Cataract Refract Surg. 2014;40:971–980. doi:10.1016/j.jcrs.2013.08.065 [CrossRef]
- Reinstein DZ, Srivannaboon S, Gobbe M, et al. Epithelial thickness changes induced by myopic LASIK as measured by Artemis very high frequency digital ultrasound. J Refract Surg. 2009;25:444–450. doi:10.3928/1081597X-20090422-07 [CrossRef]
- Hjortdal JØ, Vestergaard AH, Ivarsen A, Ragunathan S, Asp S. Predictors for the outcome of small-incision lenticule extraction for myopia. J Refract Surg. 2012;28:865–871. doi:10.3928/1081597X-20121115-01 [CrossRef]