Small incision lenticule extraction (SMILE) was developed to treat refractive errors by creating a full refractive lenticule using a photodisruptive femtosecond laser. SMILE is now a common corneal refractive procedure used to treat myopia and myopic astigmatism. It can yield visual outcomes comparable to those of laser in situ keratomileusis (LASIK).1–3 SMILE does not involve the creation of a corneal flap; thus, it does not entail any corneal flap-associated complications. However, the surgeon must dissect and extract the laser-generated refractive lenticule, so mastering the procedure involves a learning curve that is relatively flat at the beginning.4–6
Failure of separation or extraction of the refractive lenticule is a comparatively common intraoperative complication when the procedure is performed by inexperienced surgeons.7 When complete separation of the refractive lenticule is not achieved, the lenticule can be torn and become irregularly shaped. The incidence of lenticule tearing is reportedly approximately 0.3%.8 If the torn lenticule is not completely extracted, the residual lenticule fragment is retained inside the stromal pocket. In cases where a remnant lenticule fragment is located in the periphery, the effects on refractive outcome are minimal, but if the fragment is located centrally it is likely to induce irregular astigmatism and compromise the postoperative visual outcome substantially. Ganesh et al7 reported visual acuity improvement and corneal topographic regularization after surgical removal of a retained lenticule fragment. Another study reported delayed surgical removal of a retained lenticule after primary SMILE.9
In the current case, removing the retained lenticule fragment was not considered because the refractive lenticule was already torn inside the stromal pocket, rendering it a highly irregularly shaped fragment. We performed transepithelial photorefractive keratectomy (PRK), and this report describes the surgical procedure and outcomes. To our knowledge, this is the first report describing treatment with transepithelial PRK for a retained lenticule fragment after primary SMILE.
Patients and Methods
This study was conducted at Yonsei University College of Medicine, Seoul, Republic of Korea. Institutional review board approval was obtained (No. 4-2019-0622), and the protocol followed the tenets of the Declaration of Helsinki and good clinical practice. Informed consent was waived because of the retrospective nature of the study.
A 23-year-old man was referred to the Department of Ophthalmology, Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea, for the management of a retained lenticule fragment in the right eye 3 months after primary SMILE. According to his medical records, primary SMILE had been successfully performed in the left eye, and his original refractive errors were −1.00 −0.75 × 180° in the right eye and −1.25 −0.75 × 180° in the left eye.
At the time of his first visit, the uncorrected distance visual acuity (UDVA) was 20/200 and his corrected distance visual acuity (CDVA) was 20/100 in his right eye. In his left eye, both UDVA and CDVA were 20/20. The refractive error in the right eye was −6.50 −2.25 × 90°. Corneal tomography (Pentacam; Oculus Optikgeräte GmbH) revealed a central island and a high degree of anterior surface irregularity in the right eye. Anterior segment optical coherence tomography (AS-OCT) (RTVue; Optovue) depicted a hypo-reflective lesion resembling a retained lenticule fragment in the corneal stroma, and it corresponded with an opaque lesion detected via slit-lamp examination. He was observed for 11 months, by which time the corneal tomography findings and refractive status had stabilized (Figure 1).
Slit-lamp examination at the preoperative visit using (A) direct illumination and (B) retroillumination. Anterior segment optical coherence tomography image of the retained lenticule fragment (C) before and (D) 6 months after transepithelial photorefractive keratectomy.
Surgical management for the retained lenticule fragment was planned at the Eyereum Eye Clinic, Seoul, Republic of Korea, using transepithelial PRK by the surgeon (DSYK). The treatment aimed to reduce the corneal surface irregularity in the right eye and correct the remaining refractive errors. The preoperative refractive error had evidently stabilized at −4.00 −3.25 × 50° for several months. The preoperative corneal tomography image is shown in Figure 2A. Before the retreatment in the right eye, UDVA was 20/100, CDVA was 20/30, and central corneal thickness was 587 µm. Corneal epithelial mapping images were acquired via AS-OCT (Figure 2D). The location of epithelial thinning in the epithelial map corresponded to the previously detected inferior paracentral island evident in the preoperative axial curvature map. Corneal epithelial thickness in the center was 47 µm, maximum epithelial thickness in the inferonasal area was 75 µm, and minimum epithelial thickness in the inferior para-central area was 44 µm. The maximum and minimum cap thickness were 137 and 112 µm, respectively (Figure 1C). Ablation planning was performed using the integrated Optimized Refractive Keratectomy-Custom Ablation Manager software (version 5.1; SCHWIND eye-tech-solutions) based on manifest refraction, pachymetry, and corneal wavefront data (up to the 7th order) obtained via a corneal topographer (Keratron Scout; Optikon). Higher order aberrations (HOAs) were treated using the corneal wavefront-guided ablation profile. Optical zone diameter was set to 7.3 mm and the total ablation zone diameter was 9 mm. The amount of correction was −2.50 −3.00 × 50°. The ablation map is shown in Figure 2F.
Scheimpflug axial curvature map (A) before transepithelial photorefractive keratectomy (tPRK), (B) 6 months after tPRK, and (C) difference map between the two visits. Anterior segment optical coherence tomography corneal epithelial map (D) before tPRK and (E) 6 months after tPRK. (F) tPRK ablation map.
Transepithelial PRK was performed with an excimer laser platform (Amaris 1050RS; SCHWIND eyetechsolutions). The epithelium and stroma were ablated using a single continuous profile. Ablation depth at the central cornea was 104 µm, and the respective maximum and minimum ablation depths were 126 and 65 µm. After ablation, 0.02% mitomycin C was applied for 30 seconds, and the eye was then thoroughly irrigated. Topical levofloxacin (0.5%) was instilled, and a bandage contact lens was applied. The contact lens was maintained for 5 days, by which time the corneal epithelium had completely healed. Postoperative medication included topical application of 0.5% levofloxacin and 0.1% fluorometholone. Both eye drops were applied four times a day for 1 month. The steroid eye drops were gradually reduced over 3 months.
A month after the treatment, both UDVA and CDVA were 20/30, and the refractive error was +0.50 −0.50 × 150° in the treated eye. At the 6-month postoperative visit, UDVA and CDVA in the right eye were both 20/20, and the refractive error was −0.50 diopters. The patient did not report any visual symptoms. The corneal tomography image acquired at the postoperative 6-month visit is shown in Figure 2B, and the difference map is shown in Figure 2C. The corneal epithelial map obtained at the postoperative 6-month visit is shown in Figure 2E. Corneal irregular astigmatism and the central island of elevation were almost normalized. AS-OCT revealed the presence of a hyporeflective lesion suggesting a retained lenticule, but the preoperative irregular reflectivity had disappeared (Figure 1D).
Corneal wavefront aberrometry results are shown in Table 1. Postoperative 1-month results indicated considerable reduction of coma, trefoil, spherical aberration, and root mean square of total corneal HOAs. Postoperative 6-month corneal wavefront aberrations were stable, which was similar to the postoperative 1-month results.
Corneal Wavefront Aberrations (µm) in the Right Eye (7-mm Pupil)
Separating and extracting the refractive lenticule during SMILE surgery can be difficult, particularly for inexperienced surgeons. Failure of separation and complete extraction of the refractive lenticule can lead to tearing of the lenticule and a lenticule fragment can be retained in the stromal pocket. When treating an eye with a low degree of myopia with SMILE, as in the current case, the refractive lenticule may be more vulnerable to tearing because it is relatively thin. The retained lenticule fragment may induce central or paracentral elevation of the anterior corneal surface, resulting in irregular astigmatism and a high degree of corneal HOAs.
Few studies have described the management of a retained lenticule or lenticule fragment after primary SMILE surgery.7,9,10 In these studies, the retained lenticules or lenticule fragments were removed by either surgical exploration or corneal flap creation, and the results were generally good. In our case, the surgeon who performed the primary SMILE procedure failed to identify the cap plane, and approached the lenticule plane first instead of the cap plane. Accordingly, the operator attempted to find the cap interface in the wrong plane by moving a surgical instrument repeatedly in the posterior corneal stroma. We surmise that this caused intense stromal edema and corneal tissue damage, which may make it more difficult for a surgeon to separate and extract the refractive lenticule. Finally, the primary SMILE procedure was performed without extracting the entire refractive lenticule from the corneal pocket. We concluded that any attempt to separate the retained lenticule fragment from the corneal stroma would entail a high risk of failure and was likely to cause additional damage to the corneal stroma. The surgeon (DSYK) decided to perform transepithelial PRK to avoid further corneal damage. In addition, there was a report that transepithelial photo-therapeutic keratectomy could be a safe and effective method to reduce stromal surface irregularities.11 The expected depth of ablation for transepithelial PRK was less than the original cap thickness measured via AS-OCT; therefore, direct activation of the corneal wound healing process by re-treatment at the location of the retained lenticule fragment could be avoided. Although the ablation was planned above the original cap interface, 0.02% mitomycin C was applied for 30 seconds to minimize the risk of corneal haze formation.
The primary goal of the re-treatment was to reestablish a regular corneal surface. Thus, the ablation profile was optimized with corneal wavefront aberrations to minimize corneal surface irregularities. The surgeon set a relatively large optical zone (7.3 mm) to reduce the incidence of corneal optical aberrations, postoperative visual disturbances, and myopic regression. The surgeon determined an amount of photoablation that was not likely to overcorrect the patient's refractive abnormality while keeping the maximum ablation depth smaller than the original cap thickness.
According to the study by Hsu et al,12 wavefront-guided re-treatment offset after myopic LASIK was performed keeping the central ablation depth and the intended cylinder correction constant while adjusting the amount of spherical correction, and there was no case of refractive overcorrection. In addition, risk of overcorrection was reported treating highly aberrated eyes using a wavefront-guided excimer laser platform.13 The adjustment of the amount of correction was based on the aforementioned premises, but also considered several objective elements, including the use of transepithelial PRK, application of corneal wavefront, a wide optical zone, limiting the maximum ablation depth, and the expected keratometry readings after the original correction, which was attempting to achieve with-the-rule astigmatism.
To avoid lenticule tearing during SMILE in eyes with low myopia as this case, increasing the minimum lenticule thickness can be an option. Siedlecki et al14 reported that eyes with greater minimum lenticule thickness showed better safety and efficacy of SMILE. However, increased minimum lenticule thickness was associated with less undercorrection in the retrospective multicenter study.15 Therefore, adjusting the minimum lenticule thickness with caution could be helpful to separate the lenticule during SMILE in eyes with low myopia for less experienced surgeons.
Postoperative visual and refractive outcomes indicated that the re-treatment had been effective and safe. Irregular astigmatism and corneal HOAs were almost normalized after transepithelial PRK, and the patient was satisfied with the results of re-treatment.
In the current case, an irregular corneal surface caused by a retained lenticule fragment after primary SMILE was effectively corrected by transepithelial PRK. Additionally, the postoperative 6-month results indicated stable and predictable surgical outcomes. We believe that transepithelial PRK can be a safe and effective option for treating a retained lenticule fragment after primary SMILE.
- Ang M, Ho H, Fenwick E, et al. Vision-related quality of life and visual outcomes after small-incision lenticule extraction and laser in situ keratomileusis. J Cataract Refract Surg. 2015;41(10):2136–2144. doi:10.1016/j.jcrs.2015.10.049 [CrossRef]
- Damgaard IB, Ang M, Farook M, Htoon HM, Mehta JS. Intraoperative patient experience and postoperative visual quality after SMILE and LASIK in a randomized, paired-eye, controlled study. J Refract Surg. 2018;34(2):92–99. doi:10.3928/108159 7X-20171218-01 [CrossRef]
- Reinstein DZ, Archer TJ, Gobbe M. Small incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomes. Eye Vis (Lond). 2014;1(1):3. doi:10.1186/s40662-014-0003-1 [CrossRef]
- Ivarsen A, Asp S, Hjortdal J. Safety and complications of more than 1500 small-incision lenticule extraction procedures. Ophthalmology. 2014;121(4):822–828. doi:10.1016/j.ophtha.2013.11.006 [CrossRef]
- Osman IM, Awad R, Shi W, Abou Shousha M. Suction loss during femtosecond laser-assisted small-incision lenticule extraction: incidence and analysis of risk factors. J Cataract Refract Surg. 2016;42(2):246–250. doi:10.1016/j.jcrs.2015.10.067 [CrossRef]
- Wong CW, Chan C, Tan D, Mehta JS. Incidence and management of suction loss in refractive lenticule extraction. J Cataract Refract Surg. 2014;40(12):2002–2010. doi:10.1016/j.jcrs.2014.04.031 [CrossRef]
- Ganesh S, Brar S, Lazaridis A. Management and outcomes of retained lenticules and lenticule fragments removal after failed primary SMILE: a case series. J Refract Surg. 2017;33(12):848–853. doi:10.3928/1081597X-20171004-01 [CrossRef]
- Wang Y, Ma J, Zhang J, et al. Incidence and management of intraoperative complications during small-incision lenticule extraction in 3004 cases. J Cataract Refract Surg. 2017;43(6):796–802. doi:10.1016/j.jcrs.2017.03.039 [CrossRef]
- Tong JY, Cherepanoff S, Males JJ. SMILE rescue: delayed lenticule removal in a patient with high myopia. J Refract Surg. 2017;33(3):199–202. doi:10.3928/1081597X-20170104-01 [CrossRef]
- Ganesh S, Brar S, Manasa KV. CIRCLE software for the management of retained lenticule tissue following complicated SMILE Surgery. J Refract Surg. 2019;35(1):60–65. doi:10.3928/108159 7X-20181120-01 [CrossRef]
- Reinstein DZ, Archer TJ, Dickeson ZI, Gobbe M. Transepithelial phototherapeutic keratectomy protocol for treating irregular astigmatism based on population epithelial thickness measurements by Artemis very high-frequency digital ultra-sound. J Refract Surg. 2014;30(6):380–387. doi:10.3928/108159 7X-20140508-01 [CrossRef]
- Hsu YR, Shen EP, Hsieh YT, Chang HW, Hu FR. Aspheric ablation depth as the target depth for enhanced wavefront-guided myopic retreatments after laser-assisted in situ keratomileusis. Cornea. 2015;34(12):1577–1581. doi:10.1097/ICO.0000000000000640 [CrossRef]
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- Siedlecki J, Luft N, Keidel L, et al. Variation of lenticule thickness for SMILE in low myopia. J Refract Surg. 2018;34(7):453–459. doi:10.3928/1081597X-20180516-01 [CrossRef]
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Corneal Wavefront Aberrations (µm) in the Right Eye (7-mm Pupil)
|Parameter||Preoperative||Postoperative 1 Month||Postoperative 6 Months|
|Total HOA RMS||3.758||0.647||0.923|