Ye's Swing Technique for Small-incision Lenticule Extraction Surgery

Summary

We introduced an optimized surgical approach for small incision lenticule extraction, termed the Ye's Swing Technique. This technique enables the surgeon to perform lenticule separation and extraction more easily while minimizing the risk of incision-edge tears and lenticule fragmentation. The results of this study proved its safety and efficacy.

Abstract

We propose a novel approach for small incision lenticule extraction (SMILE) surgery, termed the Ye's Swing Technique. The separation and removal of the lenticule are among the most challenging steps of SMILE surgery. An improper technique can result in difficulties during lenticule extraction, lenticule rupture, and the presence of residual fragments. This technique was developed to address intraoperative challenges by preserving an unseparated peripheral edge on the posterior surface of the lenticule-a feature absent in conventional methods. In this study, 490 eyes with myopia or myopic astigmatism and lenticule thicknesses ranging from 52-148 µm were included, of which 38.6% were classified as thin lenticules. The results demonstrated that the stromal lenticule could be successfully dissected and completely removed in all participants without any incidence of incision margin tearing. The safety index was 1.06 ± 0.12, and the efficacy index was 1.11 ± 0.13 at 1 week postoperatively. These findings indicate that the modified technique is safe and effective, even with thinner lenticules.

Introduction

Over the past decade, small incision lenticule extraction (SMILE) has been frequently used for myopia correction. Although the lenticule scanning step in SMILE is fully automated using a femtosecond laser, the lenticule separation and extraction processes remain surgeon-dependent. These manual steps require substantial technical proficiency and may be associated with complications such as lenticule breakage or remnant fragments^1,2,3,4. Such complications can lead to stromal damage, heightened inflammatory responses, delayed visual recovery, and more severe issues such as diffuse lamellar keratitis, corneal opacities, and compromised visual quality^5,6.

The goal of this study is to introduce and evaluate a novel technique, the Ye's Swing Technique, designed to enhance lenticule separation and extraction during SMILE. The rationale behind developing this approach is to address existing challenges: less experienced surgeons and those working with low myopia cases often face greater difficulty performing these critical steps^7,8,9, with large-scale studies reporting an intraoperative complication rate of approximately 1.9%¹⁰. This includes incision-edge tears at 1.8%, corneal cap perforations at 0.3%, and major tears at 0.1%¹¹. Additionally, lenticule tearing has been observed in 0.27% of cases in other studies⁴.

To improve outcomes, various modified lenticule separation techniques have been proposed^12,13,14,15. However, these approaches primarily focus on reducing friction during lenticule separation without adequately addressing the lenticule's fragility at its most stressed points. Unlike traditional methods, Ye's Swing Technique deliberately preserves a residual peripheral zone on the posterior surface of the lenticule -- a feature absent in conventional approaches¹⁶. This innovation mitigates the risk of fragmentation in highly stressed areas, decreasing the chances of lenticule deformation and tearing, particularly in thinner lenticules.

This technique is intended for the lenticule separation and extraction steps following the scanning process in SMILE surgery (when no obvious black zones appear during scanning) and is particularly well-suited for cases involving thin lenticules. To aid readers in evaluating the applicability of this method, we provide a detailed description of the technique and analyze its postoperative visual outcomes and complications.

Protocol

This prospective study consecutively included patients who underwent SMILE surgery between May 1^st and July 30^th, 2022, at the Eye Hospital of Wenzhou Medical University, Hangzhou, China. All the surgical procedures were performed by the same ophthalmologist. This study was conducted in accordance with the principles of the Declaration of Helsinki. Ethical approval was obtained from the Ethics Committee of the Eye Hospital of Wenzhou Medical University (No. H2022-002-K-02-01), and written informed consent was obtained from all participants.

1. Patient selection

NOTE: A total of 246 patients (490 eyes) were included in this study, with a mean age of 26.66 ± 7.44 years (range, 18 to 46 years), and 43.5% of the participants were male.

1. Use the following inclusion criteria.
   1. Ensure the spherical equivalent power is > -10.0 D. Confirm the refractive status has remained stable for at least 2 years. Verify that corrected distance visual acuity (CDVA) > 20/25 (Snellen acuity).
2. Use the following exclusion criteria.
   1. Exclude patients with central corneal thickness < 480 µm. Exclude patients with corneal topography suggestive of keratoconus or evidence of cataract, ocular inflammation, or other active ocular diseases identified during preoperative examinations.
3. Perform contact lens wear management as described below.
   1. Instruct soft contact lens wearers to discontinue use for at least 2 weeks before surgery.
   2. Advise rigid contact lens wearers to stop use for at least 4 weeks preoperatively.
   3. Require orthokeratology lens wearers to cease usage for a minimum of 3 months before surgery.

2. Preoperative examination

1. Uncorrected distance visual acuity (UDVA): Measure UDVA using a standardized LogMAR chart at a distance of 5 m.
2. Subjective refraction and corrected distance visual acuity (CDVA): Perform an initial autorefraction, followed by refinement of the measurements using a phoropter to determine the sphere, cylinder, and axis, ensuring optimal corrected visual acuity under standardized conditions.
3. Slit-lamp biomicroscopy: Examine the anterior segment of the eye (eyelid margins, conjunctiva, cornea, anterior chamber, iris, and lens) using a slit-lamp. Use a fundus lens to evaluate the posterior segment (vitreous, optic disc, and retina).
4. Intraocular pressure: Measure intraocular pressure using non-contact tonometry. Participants were seated comfortably with proper head positioning and instructed to fixate on the internal target. The tonometer, aligned centrally with the cornea, delivered an air puff automatically recording intraocular pressure. Measurements were repeated three times per eye, and the average was used for analysis.
5. Scheimpflug-based corneal topography: Perform corneal topography using the Pentacam HR (Type 70900). Instruct the patient to fixate on the internal target while the examiner aligned the device with the corneal apex. Only results labeled OK with a quality score exceeding 95% are considered valid.
6. Spectral-domain optical coherence tomography (SD-OCT): Anterior segment imaging was performed using SD-OCT. Seat the participants with proper head alignment and instruct them to fixate on the internal target. Acquire cross-sectional images of the cornea in high-resolution mode.

3. Surgical technique

1. Anesthetization: Prior to SMILE surgery, instill one drop of topical anesthetic (0.5% proparacaine hydrochloride) into the conjunctival sac approximately 5 min before the procedure, followed by a second application about 10 s before initiation to ensure optimal anesthesia. The surgeon should then verify adequate corneal anesthesia by gently touching the corneal surface with a swab to confirm minimal patient discomfort.
2. Lenticule scanning: Perform the lenticule scanning step using a femtosecond laser system (500 Hz) with a pulse energy 140 nJ. Set the following parameters: a lenticule diameter of 6.0-7.0 mm, an intended cap thickness of 110-120 µm, a 0.10 mm transition zone for cylindrical errors, and a 2 mm incision at 110°.
3. Use Ye's Swing Technique for lenticule separation and extraction, as follows: Open the full-length corneal cap incision from left to right using a small surgical hook. Dissect half the length of the lenticule incision from right to left (Figure 1A).
4. Use a blunt spatula to separate the anterior surface of the lenticule. Start at the 8 o'clock position (Figure 1B, point a) and proceed counterclockwise to the 12 o'clock position (Figure 1B, point d). Leave the remaining portion of the lenticule undisturbed to prevent displacement.
5. Insert a blunt spatula underneath the posterior surface of the lenticule and proceed with partial counterclockwise dissection from the 8 o'clock position (Figure 1C, point a) to the 4 o'clock position (Figure 1C, point c), preserving the peripheral edge zone of the lenticule. Subsequently, guide the spatula along the peripheral edge toward the 12 o'clock position (Figure 1D, point d).
6. Grasp the free edge of the lenticule using femtosecond lenticule forceps, push it toward the center, and gently remove it using a continuous clockwise tearing motion (Figure 1E).
7. For left-handed surgeons, reverse all procedural directions.
8. Examine the integrity of the lenticule under the surgical microscope. Gently smooth the corneal cap and incision using an irrigation needle to complete the procedure.

4. Postoperative management

1. After surgical procedures, add a drop of tobramycin dexamethasone at the surgical site.
2. Following surgery, instruct patients to use 0.5% levofloxacin eye drops 4x daily for 1 week. Subsequently, instruct to use 0.1% fluorometholone eye drops 4x daily, and taper the dose to one instillation per week. Additionally, administer artificial tears 4x daily for 3 months.

5. Outcome evaluation

1. Primary outcome measures
   1. Assess lenticule integrity microscopically after extraction. Under the surgical microscope, flatten and examine the lenticule to ensure it forms a complete circular shape with no edge defects.
   2. AT 1 day after surgery, perform SD-OCT using the Line scan mode to detect any residual lenticule fragments between the stromal layers. Ask the technician to adjust the handle according to the indicator arrow on the screen, allowing the instrument to scan automatically once properly focused. Consider results with an imaging quality marked as OK and a quality score exceeding 95% as valid for analysis.
   3. Calculate the safety index as the ratio of postoperative CDVA to preoperative CDVA¹⁷.
2. Secondary Outcome Measures
   1. Determine surgical efficacy by calculating the efficacy index as the ratio of the postoperative UDVA to the preoperative CDVA¹⁷. For the measurement methods for UCVA and CDVA, follow the same procedures as those used preoperatively, as described in steps 2.1 and 2.2.
3. Follow-up
   1. Do not hospitalize the patients and schedule for follow-up examinations 1 day and 1 week after surgery. Evaluate UDVA, CDVA, subjective refraction, corneal topography, SD-OCT, and complications on postoperative day 1 and at 1 week.

Results

Ye's Swing Technique was successfully applied to 246 patients (490 eyes). Table 1 summarizes the clinical characteristics and postoperative data of enrolled patients. The lenticule thickness was 106.30 ± 23.27 µm (ranging from 52-148 µm), with 38.6% classified as thin lenticules (<100 µm).

Using Ye's Swing Technique, lenticule dissection and extraction can be completed in approximately 30-60 s. All lenticules were extracted completely and successfully. No incision-edge tear...

Discussion

Lenticule separation and extraction are the most challenging steps of SMILE. Inappropriate manipulation during this process may lead to complications such as incision-edge tears, corneal cap tears, epithelial defects, lenticule remnants, and delayed visual recovery⁴. In certain difficult cases, repeated attempts at lenticule dissection may be required, increasing corneal tissue manipulation and prolonging the surgical time¹⁹. This study describes the Ye's Swing Tec...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.1% fluorometholone	Allergan, Inc.	H20181090
0.5% levofloxacin	Santen, Inc.	H20150278
0.5% proparacaine hydrochloride	Alcon, Inc.	HJ20160133
Blunt spatula	Suzhou Mingren Medical Equipment Co., Ltd	INTRALASIK FLAP SPATULA, MR-G134T-4
Corneal topography system	Oculus, Wetzlar, Germany	OCULUS Pentacam HR 70900
Femtosecond lenticule forceps	Suzhou Xiehe Medical Devices Co., Ltd.	MR-G116T-4
Non-contact tonometer	Topcon, Japan	CANON TX-F
Small surgical hook	Suzhou Mingren Medical Equipment Co., Ltd	INTRALASIK FLAP SPATULA, MR-G134T-4
Spectral-domain optical coherence tomography	Optovue Inc., CA, USA	Optovue RTVue XR
Tobradex (tobramycin dexamethasone)	Alcon, Inc.	H20150119
VisuMax femtosecond laser system (500 Hz)	Carl Zeiss Meditec AG, Germany	ZEISS VisuMax