Small Incision Lenticule Extraction Technique Research Articles

OUTCOMES COMPARISON AFTER SMALL INCISION LENTICULE EXTRACTION (SMILE) AND FEMTOSECOND-LASER ASSISTED IN SITU KERATOMILEUSIS (FS-LASIK) IN LOW-MODERATE MYOPIA PATIENTS

Abstract
 Introduction & Objectives : Uncorrected myopia is the leading cause of visual impairment globally. It can be corrected by refractive surgeries, such as Small Incision Lenticule Extraction (SMILE) and Femtosecond Laser- Assisted In Situ Keratomileusis (FS-LASIK). SMILE technique is less-invasive than FS-LASIK, characterized by all-in-one femtosecond laser and flapless procedure. Correction of low-moderate myopia requires a special concern because even slight decreased in visual quality may be noticed by the patients and affect their satisfaction. The purpose of this study to compare the refractive outcomes after SMILE and FS-LASIK in low-moderate myopia patients.
 Methods : This is a prospective analytical observational study that was conducted in a tertiary hospital in Indonesia. Four refractive outcome parameters (predictability, efficacy, safety, and stability) were assessed at 1 day, 1 week, and 1 month postoperatively.
 Results : SMILE was performed on 22 eyes with spherical equivalent (SE) -3.60±1.07 D and FS-LASIK on 20 eyes with SE -2.91±1.53 D. At 1 month, the predictability as the proportion of eyes within SE ±0.50 D were 95.5% in SMILE and 80% in FS-LASIK (p=0.174), the efficacy as the proportion of eyes achieving uncorrected distant visual acuity (UDVA) ≥20/20 were 63.6% in SMILE and 35% in FS- LASIK (p= 0.064), the stability as the proportion of eyes experiencing SE change >0.50 D were 4.5% in SMILE and 5% in FS-LASIK (p=1.000). No eyes from both groups had corrected distant visual acuity (CDVA) loss of ≥2 lines (p=1.000).
 Conclusion : SMILE and FS-LASIK were both predictable, effective, safe, and stable for low-moderate myopia patients.

Histopathology of Corneal Lenticules Obtained from Small Incision Lenticule Extraction (SMILE) versus Microkeratome Excision.

To study the alterations on the lenticules extracted after femtosecond (Femto) small incision lenticule extraction (SMILE) versus the corneal free cap removed using a microkeratome. The visuMax (500 kHz; laser energy: 180 nJ) was used for small-incision lenticule extraction. Free caps from human cadaveric corneas were excised by microkeratome. The collected lenticules were examined with the light and transmission electron microscope (TEM) for histological analysis, DNA fragmentation was assessed by agarose gel electrophoresis, DNA damage was evaluated using comet assay, and corneal proteins secondary structure was assessed by Fourier transform infrared spectroscopy (FTIR). Light microscopic examination showed the presence of more edematous stroma under Femto SMILE than under free cap with a percentage change of 101.6%. In the Femto SMILE group, TEM examination showed pyknotic keratocytes, disruption, and cavitation of the collagen arrays stromal area under Femto SMILE. The DNA fragmentation for the Femto SMILE group revealed one undefined band with a size of 1.1 Kbp. The comet assay analysis indicated the presence of 3% and 8.0% tailed cells for the free cap and Femto SMILE groups, respectively. The tail lengths were 1.33 0.16 and 1.67 0.13 µm (P 0.01), the percentage of tail DNA was 1.41 0.18% (P 0.01) and 1.72 0.15%, and the tail moments were 1.88 0.12 AU and 2.87 0.14 AU (P 0.001) for the free cap and Femto SMILE groups, respectively. FTIR spectroscopy of the Femto smile group revealed disorders in the secondary and tertiary structure of the proteins. Femto SMILE technique induced more structural changes, DNA fragmentation, DNA damage, and corneal proteins secondary structure alteration than those induced by a microkeratome cutting. These changes may be attributed to the deep penetration of high energy levels to the corneal layer. These findings may highlight the potential impact of the Femto SMILE on the cornea and the necessity for managing the laser parameters used.

SMILE - Small Incision Lenticule Extraction

Refractive lenticule extraction is a corneal surgical technique that uses a femtosecond laser exclusively to create an intrastromal refractive lenticule for the correction of myopia and myopic astigmatism. In small incision lenticule extraction (SMILE) the generated refractive lenticule is subsequently extracted through a small incision. The reported efficacy, predictability and safety of the flap-less SMILE procedure is similar to those of femtosecond laser in situ keratomileusis (LASIK). Advantages of SMILE over LASIK include less iatrogenic dry eye, fewer induced higher-order aberrations, and potentially less biomechanical weakening of the cornea. However, there is a steeper surgeon learning curve for SMILE as the procedure is technically more challenging than LASIK. Furthermore, the current SMILE laser platform cannot use cyclotorsion control or eye-tracking technology and retreatment options are more complex compared to LASIK. This review looks at patient selection, surgical method, possible complications, retreatment options, and postoperative outcome of the SMILE technique.

Long-Term Refractive Outcome of Small Incision Lenticule Extraction in Very High Myopia

To assess the stability, safety, predictability, and efficacy of small incision lenticule extraction (SMILE) in high myopia. The study was conducted as a retrospective noncomparative analysis of the records of 495 eyes of 270 patients treated by the ReLEx SMILE technique for a mean spherical myopic error of -12.84 ± 2.47 D (range: -10.0 to -14.0 D) combined with a mean astigmatism of -1.17 ± 1.34 D (up to -4.0 D). The mean LogMAR corrected distance visual acuity (CDVA) was 0.2 ± 0.6. In this study, 225 patients had the bilateral SMILE procedure, whereas 45 patients had a single eye treated with SMILE. One month after surgery, the mean refractive error was 20.72 ± 0.88 D (range: +1 to 21.5 D), and the mean postoperative astigmatism was -0.83 ± 1.04 D. The mean LogMAR UDVA was 0.2 ± 0.34. In the last follow-up visit, 3 years after surgery, all the before mentioned parameters were the same or within minimal changes with no statistically significant difference from the earlier results. However, the spherical error demonstrated a significant change from -0.72 ± 0.88 D at 1 month to -1.17 ± 1.01 D at the end of the follow-up. However, this change had an insignificant visual impact. At the end of the follow-up period, approximately 94% of patients had unchanged CDVA or gained one or more lines, 6% lost one line of CDVA, and 1% lost 2 lines. SMILE may be effective and safe, with a stable and predictable outcome for correction of very high myopia.

Comparison of Visual, Refractive and Ocular Surface Outcomes Between Small Incision Lenticule Extraction and Laser-Assisted In Situ Keratomileusis for Myopia and Myopic Astigmatism.

Laser-assisted in situ keratomileusis (LASIK) is the most commonly performed laser refractive surgical technique worldwide for the treatment of myopia and myopic astigmatism. In recent years, small incision lenticule extraction (SMILE) has emerged as a promising alternative to LASIK, requiring only a single femtosecond laser to create an intrastromal lenticule, which is then removed via a small incision. The technique obviates the need for a corneal flap. A number of published studies have compared the two techniques in terms of visual, refractive and ocular surface outcomes. This review compares the clinical outcomes between LASIK and SMILE in treating myopia and myopic astigmatism based on studies published in the last 5 years. Twenty-two studies were included, all of which were observational in nature. Results suggest that the two techniques have comparable visual outcomes in terms of safety, efficacy and predictability, although recovery in visual acuity may be slower in SMILE-treated than LASIK-treated eyes. SMILE is found to result in less severe postoperative dry eye symptoms and faster recovery of corneal sensitivity than LASIK. It is important to note, however, that the SMILE technique is limited by the lack of a cyclotorsion-compensation system and option for customized treatment profile. The heterogeneity of results in this review may be attributable to the use of different LASIK platforms in different studies. Few studies compared the outcomes regarding severity of myopia. Future prospective randomized controlled trials with a larger sample size and longer follow-up period will be highly beneficial for progress in this field.

SMILE keratorefractive surgery technique

Small incision lenticule extraction (SMILE) keratorefractive surgery technique is a laser surgery alternative to common methods that doesn't require laser ablation of the cornea. Despite its novelty, SMILE technique has already demonstrated positive clinical results comparable to Photorefractive Keratectomy (PRK) and Laser-Assisted in Situ Keratomileusis (LASIK), which led to its widespread application in clinical practice. Compared with other keratorefractive techniques, SMILE has a number of distinct advantage including high biomechanical stability of the cornea, low risk of dry eye syndrome, absence of a corneal flap and associated complications, preservation of corneal epithelium. The article describes the most common SMILE modifications, its weak points and possible complications, as well as methods of additional correction of remaining ametropy.

Femtosecond Laser-Assisted Small Incision Endokeratophakia Using a Xenogeneic Lenticule in Rhesus Monkeys.

To evaluate the feasibility and safety of xenogeneic endokeratophakia in rhesus monkeys and to explore the effects of a concave lenticule on refractive power. Three adult New Zealand white rabbits and 6 healthy rhesus monkeys were used. The xenogenic concave grafts were created from the rabbits using a modified small incision lenticule extraction technique; after being cryopreserved in glycerol for 1 week, the grafts were implanted into the monkey recipient corneas. Spherical equivalent (SE), central corneal thickness, and keratometry curvature were assessed preoperatively, 1 week, 1, 4 and 6 months postoperatively. The quality of the xenogenic graft was also assessed by slit-lamp microscopy, in vivo confocal microscopy, and optical coherence tomography with anterior segment imaging. The graft appeared to be swollen a day after the operation but reduced considerably after a week. A trend of a lower refractive power (hyperopic shift) was demonstrated in relation to the SE after concave graft implantation. The mean SE increased from -0.60 ± 1.31 (median -0.69, interquartile range -1.00 to 0.50) preoperatively to 0.75 ± 1.27 (median 1.38, interquartile range -0.25 to 1.63) at 1 month postoperatively (P = 0.01). Central corneal thickness was significantly thicker each time after surgery compared with that recorded preoperatively (P < 0.01). The anterior and posterior interface between the graft and stroma was visible during the study. Corneal nerve regeneration was evident at 6 months postoperatively. The xenogeneic concave graft was stable and transparent at follow-up. Severe adverse events or evidence of a rejection response were not observed. Femtosecond laser-assisted small incision endokeratophakia using a xenogeneic corneal lenticule seems to be feasible and safe, which may provide a new method for myopia correction and keratoconus treatment.

Lenticuloschisis: A "No Dissection" Technique for Lenticule Extraction in Small Incision Lenticule Extraction.

To describe a "no dissection" technique of lenticule removal in small incision lenticule extraction (SMILE). After docking and laser delivery, a microforceps is used to grasp and gently peel off the lenticule from the underlying stromal bed, without performing any dissection of the upper and lower planes of the lenticule. Prerequisites are a surgeon experienced in the conventional SMILE technique, optimized laser energy settings, and a minimum peripheral lenticule thickness of 25 to 30 µm. The interface as assessed in postoperative dilated clinical photographs was seen to be clearer with less roughness compared to the conventional dissection technique. This may potentially result in better first postoperative visual acuity and quality of vision due to less corneal tissue trauma and minimal tissue handling, thus potentially resulting in faster visual recovery. No dissection lenticule removal is a feasible and reproducible technique that may result in better immediate visual quality compared to the conventional SMILE technique. [J Refract Surg. 2017;33(8):563-566.].

Refraction outcomes after suction loss during small-incision lenticule extraction (SMILE).

PurposeTo evaluate refractive outcomes of two management approaches after suction loss during the small-incision lenticule extraction (SMILE) technique.Patients and methodsThis retrospective and comparative study was conducted at the El-Gowhara Private Eye Center. It included 26 consecutive eyes of patients who experienced suction loss during the SMILE technique. Patients were divided into two groups by the technical difficulties in redocking: in group A (12 eyes) suction loss occurred after the posterior lenticular cut and the creation of side-cuts, then suction was reapplied, and the procedure was completed; in group B (14 eyes) suction loss occurred after the posterior lenticular cut and the creation of side-cuts, then the procedure was postponed for 24 hours and completed with the same parameters. Manifest refraction outcomes were measured and compared 6 months postoperatively.ResultsThis study included 26 eyes with suction loss during the SMILE technique: five patients with suction loss in both eyes, nine patients with suction loss in the right eye and seven patients with suction loss in the left eye. The incidence of suction loss in this study was 2.7%. At the postoperative 6-month follow-up time, there were statistically significant differences in refraction outcomes between the two groups, with a hyperopic shift in group A compared with group B.ConclusionA good refraction outcome can be achieved with appropriate management of suction loss during the SMILE technique, and it is recommended to postpone the treatment if this happens.

Dynamic observation of corneal reinnervation after small incision lenticule extraction at cap by confocal microscope

Background Corneal reinnervation of subbasal nerve plexus have been found after small incision lenticule extraction(SMILE). However, there were few reports about corneal reinnervation mode and dynamic changes at the corneal cap in different time points postoperation. Objective The aim of this study was to evaluate the corneal reinnervation at the cap margin after SMILE. Methods The clinical data of 32 myopic eyes of 16 patients who received SMILE incision lenticule extraction surgerv in Affiliated Eye Hospital of Shandong Medical College from April 2014 to April 2015 were retrospectively analyzed.The following-up was carried in 1 week, 1 month, 3 months and 6 months after surgery, and in-vivo confocal microscopy was used to acquire images of the central corneal subbasal nerve plexus before and after surgery, with the scan range of 0.4 mm×0.4 mm, from which nerve density and nerve tortuosity were evaluated using Image-Pro Plus imaging analysis software.The overall length of nerve fibers at the central cornea was measured to assess the subbasal nerve density, and the repair of nerve fibers at cap was observed. Results The corneal subbasal nerve density was (19 687.45±1 147.59), (10 500.46±1 056.22), (12 833.40±1 047.98), (13 564.04±1 173.01) and (14 661.35±941.92)μm/mm2 in preoperation and postoperative 1 week, 1 month, 3 months, 6 months, respectively, with a significant difference among different time points (F=319.44, P=0.000), and the corneal subbasal nerve densitis in postoperative time points were significantly reduced in comparison with the preoperation, and corneal subbasal nerve densities were gradually increased after surgery as the extending of time, showing significant differences between different time points (all at P<0.01). Abundant corneal subbasal nerve fibers were seen with the near normal morphology after surgery.However, the fragments and disaggregation of nerve fibers were found at the incision of cap margins, and some nerve fibers extended toward the inner cap at the non-incision of cap margins 1 week after surgery.In 3-6 months after SMILE, the continuous extension of nerve fibers was exhibited under the confocal microscope. Conclusions Six months after surgery, less invasive SMILE technique can remain the superficial corneal nerve fibers.Corneal innervation shows a radiate mode from peripheral cornea outside toward inside of the cap.The subbasal never fiber density is gradually increased with the extending of time after SMILE. Key words: Corneal reinnervation; Cornea surgery, laser; Lasers, excimer/therapeutic use; Microscopy, confocal; Nerve regeneration/physiology; Ophthalmic nerve/physiology; Surgical flaps; Small incision lenticule extraction

Comparison of corneal hysteresis and corneal resistance factor after small-incision lenticule extraction and photorefractive keratectomy

Purpose The aim of this study was to compare the corneal hysteresis (CH) and corneal resistance factor (CRF) after small-incision lenticule extraction (SMILE) and photorefractive keratectomy (PRK). Patients and methods Fifty-six eyes of 28 patients were included in this study. The study eyes had myopia or myopic astigmatism with spherical equivalent less than or equal to −6 D. They were divided into two groups: group I (28 eyes of 14 patients) was corrected using the SMILE technique and group II (28 eyes of 14 patients) was corrected using the PRK technique. CH and CRF were measured in all eyes preoperatively and postoperatively using the ocular response analyzer instrument. Best-corrected visual acuity, spherical equivalent, and central corneal thickness were documented preoperatively and postoperatively in each follow-up visit. All patients were followed up at 3, 6, and 12 months postoperatively. Results The mean patients’ age was 23.8±4.2 years in group I and 24.1±4.7 years in group II (P=0.85). In the SMILE group, CH changed from 10.57±0.38 preoperatively to 8.6±0.26 at 12 months postoperatively (P Conclusion CH and CRF decreased after SMILE and PRK. There were no differences between SMILE and PRK treatments in postoperative CH or CRF values.

Subbasal nerve morphology, corneal sensation, and tear film evaluation after refractive femtosecond laser lenticule extraction

The purpose of this study was to compare corneal subbasal nerve morphology, corneal sensation, and tear film parameters after femtosecond lenticule extraction (FLEX) and small-incision lenticule extraction (SMILE). A prospective, randomized, single-masked, paired-eye design clinical trial of 35 patients treated for moderate to high myopia with FLEX in one eye and SMILE in the other. In both techniques, an intrastromal lenticule was cut by a femtosecond laser and manually extracted. In FLEX, a LASIK-like flap allowed removal of the lenticule, whereas in SMILE, it was removed through a small incision. In-vivo confocal microscopy was used to acquire images of the central corneal subbasal nerve plexus, from which nerve density, total nerve number, and nerve tortuosity were analyzed. Corneal sensation was measured using Cochet-Bonnet esthesiometry. A visual analog scale, tear osmolarity, non-invasive tear film break-up time (keratograph) tear meniscus height (anterior segment OCT), Schirmer's test, and fluorescein tear film break-up time were used to evaluate tear film and ocular surface symptoms. Patients were examined before and 6 months after surgery. There were no statistically significant differences in baseline parameters between FLEX and SMILE (p > 0.050). With regard to changes from before to 6 months after surgery, mean reduction in subbasal nerve density was 14.22 ± 6.24 mm/mm(2) in FLEX eyes, and 9.21 ± 7.80 mm/mm(2) in SMILE eyes (p < 0.05). The total number of nerves decreased more in FLEX eyes than in SMILE eyes (p < 0.05). No change was found when comparing tortuosity (p > 0.05). Corneal sensation was reduced with 0.38 ± 0.49 cm in FLEX eyes, and 0.10 ± 0.34 cm in SMILE eyes (p < 0.01). No differences were found between FLEX and SMILE in tear film evaluation tests (p > 0.05). Significantly more patients felt postoperative foreign body sensation in the FLEX eye within the first days after surgery, as compared to the SMILE eye. Six months after surgery, the less invasive SMILE technique seemed better at sparing the central corneal nerves as compared to FLEX. Corneal sensation was only significantly reduced in FLEX eyes. There were no differences between FLEX and SMILE when comparing tear film evaluation tests 6 months after surgery.