Small Incision Lenticule Extraction

Anatomy and Physiology

Laser refractive surgeries, including SMILE, target the cornea—the transparent, dome-shaped layer that envelops the front of the eye. Utilizing the FS laser, these procedures involve forming an intrastromal lenticule through various photoablation incisions. Subsequently, a secondary incision for lenticule extraction is made on the peripheral cornea, typically situated along the superior or superotemporal aspect.[2]

Indications

SMILE received initial approval from the US Food and Drug Administration (FDA) in 2016 for the correction of myopia ranging from -1 diopter (D) to -8 D and astigmatism up to -0.5 D in individuals aged 22 years or older.[4] In 2018, the indications were expanded to encompass myopic astigmatism up to 3D.[8] The Schwind ATOS platform currently offers correction of astigmatism up to 6D. The manifest spherical equivalent should not exceed -8.25 D of astigmatism. The European Committee (Conformité Européene) has granted approval for a correction of manifest refractive spherical equivalent (MRSE) up to -11.5 D, including -10 D of myopia and -3 D of myopic astigmatism. 

In clinical practice, additional criteria are often considered, including a mesopic pupil size less than 7 mm, residual stromal bed exceeding 250 µm, central corneal thickness (CCT) greater than 475 µm, and an expected postprocedure keratometry between 35 D and 47 D. Furthermore, patients should exhibit stable refraction within +/- 0.5 D for a minimum of 1 year before undergoing SMILE.[9] 

The preoperative ocular assessment and patient selection for SMILE align with those for flap-based procedures such as manual LASIK and Femto LASIK. It is crucial to rule out abnormal topographic patterns and forme fruste keratoconus. Additionally, for SMILE, the percentage of tissue altered (PTA) should be kept below 40%, with PTA calculated as (lenticule thickness + cap thickness)/central corneal thickness.

For individuals with preexisting dry eyes, SMILE is preferable to flap-based procedures, given its documented superiority in ocular surface stability. The sub-basal nerve fiber regeneration is rapid in SMILE, and even if dry eye symptoms develop, their severity tends to be milder with faster recovery. Hence, SMILE is considered a more feasible and better option for patients with preexisting dry eyes.

Biomechanically, SMILE demonstrates superior strength compared to LASIK, which is attributed to creating a small side cut instead of a circumferential flap. The biomechanical strength of the anterior stromal cornea is bolstered by interlamellar collagen bonds and SMILE results in less disruption of peripheral corneal fibers and the preservation of corneal biomechanical integrity. Although cases of post-SMILE ectasia have also been reported, SMILE is preferred over LASIK in instances of high refractive errors.

Several factors influence the choice between SMILE and LASIK when determining the most suitable procedure for a patient. With its absence of flap creation, SMILE may be preferred for patients engaged in contact sports, where there is a risk of traumatic flap dislocation.[9] SMILE is often elected for patients with mild preoperatively dry eye due to evidence of reduced postoperative dry eye compared to LASIK.[9] 

SMILE is associated with fewer postoperative higher-order aberrations (HOAs), such as ghosts, shadows, or glare. Therefore, SMILE may be a better option for patients with large pupils prone to experiencing these phenomena at night due to pupillary dilation.[7] However, SMILE remains a more technically challenging procedure than LASIK, with a steep learning curve,[2] making LASIK a preferred choice for novice surgeons dealing with patients with low myopia, complicated orbital anatomy, high astigmatism, or significant preoperative anxiety.[7] 

LASIK is often preferred for treating hyperopia or in cases with substantial HOAs or topographic irregularities.[9] It may also be preferred for patients with epithelial basement membrane dystrophy or corneal opacity.[9] In contrast, SMILE is an excellent option for treating myopia or astigmatism in patients without epithelial disorders or corneal abnormalities.[9] The higher-order and spherical aberrations induced with SMILE are comparatively less than with LASIK.

Patients with large pupillary diameters who may experience glare and halos after LASIK due to increased spherical aberrations often find SMILE the preferred surgery. The learning curve in SMILE is steep, and performing SMILE can be more challenging for operating surgeons in the initial phases of learning compared to LASIK.

Contraindications

Contraindications for SMILE are largely similar to those of other laser refractive surgeries (see Table. Absolute and Relative Contraindications for SMILE). These include the following:

• SMILE is not recommended for patients with known corneal thinning disorders such as keratoconus or central corneal thickness (CCT) less than 475 µm, aiming to minimize the risk of postoperative ectasia.

• SMILE is not approved for patients with uncontrolled glaucoma or uveitis, significant cataracts, corneal scarring, functional monocularity, active eye inflammation or infection, and severe dry eye or ocular allergy.

• Due to potential hormonal changes impacting visual refraction, laser refractive procedures are not advised for women who are pregnant or breastfeeding.[9]

• A history of herpes simplex keratitis may be considered a relative contraindication for SMILE, although the risk for reactivation may be minimized with preoperative and postoperative antiviral treatment.

• Other relative contraindications include irregular cornea or irregular corneal astigmatism, immunodeficiency, epithelial basement membrane dystrophy, history of autoimmune disorders, and mild dry eye or ocular allergy.

• Caution should be taken in patients with uncontrolled diabetes, as this has been demonstrated to delay corneal wound healing.[7]

Table 1. Absolute and Relative Contraindications for SMILE [7] 

Novice surgeons are advised to exercise caution and consider certain factors when selecting cases for SMILE procedures. Low myopia cases should be approached with care, as they pose challenges in separating the lenticule, potentially increasing the risk of inadvertent lenticule dissection in the wrong plane and cap lenticular adhesions.[10] For beginners, the focus can be on moderate to high myopia (above 4D), where the lenticule is thick and relatively safe and easier to handle.

Patients with challenging orbital anatomies, such as deep-set eyes, narrow palpebral fissures, or prominent noses, are predisposed to suction loss and should be avoided as initial cases. Additionally, individuals who are uncooperative or exhibit frequent ocular and head movements may pose difficulties for beginners.

Cyclotorsion can occur in patients with high astigmatism; an experienced SMILE surgeon must handle these patients.[11] By considering these factors, beginner surgeons can enhance their learning experience and gradually expand their proficiency in SMILE procedures.

Equipment

Currently, the intrastromal refractive lenticule is created exclusively using a commercially available FS laser.[7] This laser emits photons at a wavelength of 1043 nm and operates at a frequency of 500 kHz.[7] The laser offers 3 distinct modes, catering to the user's expertise, which will be discussed below.

Laser Settings and Machine Parameters

Commercially available FS laser platforms are designed to create an intrastromal refractive lenticule at a precise pre-decided depth and position. The laser system typically comprises a computer unit, a laser-firing unit, and a foot pedal switch for operational control.[12] Integrated illumination systems, such as diffuse slit and infrared illumination, are built into the machine. The patient interface (PI) involves a single-use disposable contact lens, known as the treatment pack, which includes tubing facilitating the interface between the patient and the machine.

The treatment pack is categorized based on the white-to-white diameter, denoted as small, medium, and large (S, M, and L, respectively). Laser settings are preprogrammed into the machine, and the treatment modes are categorized as standard, fast, and expert modes.[13]

The standard mode of the FS laser features default laser settings that are manufacturer programs. In the fast mode, the application specialist can adjust laser settings exclusively, offering customization based on specific regional requirements and individual needs. For advanced users, the expert mode allows modifiable laser settings that can be optimized by the surgeon before each case, offering a high degree of customization and control.[7] While the fast mode allows for a specific range of modifications in laser parameters, it is advisable, particularly during the initial learning phase for laser and parameter settings, to consult with the application engineer.[14]

Table 2. Laser Settings in Various Modes [7]

The FS laser settings can be modified to control various parameters, including spot distance, track distance, pulse energy, and energy offset (see Table. Laser Settings in Various Modes). The spot distance, which is the space between 2 nearby laser spots, ranges from 2 to 4.5 µm. Similarly, the track spacing, representing the distance between 2 laser spots in adjacent tracks, also ranges from 2 to 4.5 µm.

Pulse energy, defined as the size of cavitation bubbles produced during FS laser cuts, varies from 100 to 260 nJ, with a recommended range of 100 to 160 nJ. Energy offset, equivalent to 5 nJ of pulse energy, ranges from 20 to 52 nJ, with a recommended range of 20 to 32 nJ). The scan direction is set as spiral in for the posterior plane and spiral out for the anterior plane.[15]

Personnel

Using a FS laser in medical procedures, such as SMILE, for refractive surgery typically involves a multidisciplinary team of trained personnel. The specific roles may vary depending on the healthcare institution and local regulations, but generally, the following professionals are commonly involved:

• Ophthalmologist or refractive surgeon
• Surgical technologist or scrub nurse
• Biomedical engineer or laser technician
• Application Specialist
• Nursing staff
• Anesthesiologist or anesthetist

Preparation

Thoughtful patient selection and effective management of patient expectations are essential for optimizing visual outcomes and ensuring patient satisfaction. Providing comprehensive information regarding the risks and benefits of SMILE is essential, and obtaining informed consent is a necessary step in the process. To alleviate anxiety, patients should be informed about what sensations they might experience during the procedure, such as sounds, feelings, sights, and smells.

Thorough screening of the patient's medical history is imperative to identify any contraindications, as outlined previously. Patients should be selected only if they have realistic expectations regarding postoperative visual outcomes. It is vital to convey to patients that the primary objective of laser refractive surgery, such as SMILE, is not to achieve the complete absence of refractive error but to reduce dependence on glasses and contact lenses.

An extensive preoperative evaluation is necessary to identify potential contraindications to laser refractive surgery. The examination should encompass a comprehensive assessment of various ocular factors:

• Eyelids and tear film: Examine for signs of dry eye or blepharitis, as these conditions may impact the procedure's success.

• Refraction: Assess the patient's refraction, including refractive stability, degree of refractive error, and astigmatism. Obtain manifest and cycloplegic refraction, with disparities greater than 1 D of the sphere warranting reevaluation.

• Cornea: Inspect the cornea for scars, vessels, or signs of inflammation that may affect surgical outcomes.

• Pupil size: Measure pupil size using a commercial pupillometer to account for variations in low-light conditions.

• Slit-lamp examination: Utilize slit-lamp examination to identify corneal abnormalities such as keratoconus, neovascularization, scarring, or the presence of a cataract.

• Corneal pachymetry: Use corneal pachymetry as a screening tool for patients with corneal thinning disorders.

• Computed corneal topography: Employ computed corneal topography to detect keratoconus and irregular astigmatism.

• Intraocular pressure: Measure intraocular pressure to identify uncontrolled glaucoma.

• Fundoscopy: Conduct fundoscopy to rule out the presence of retinal holes, degenerative retina, and other types of macular disease.

• Computed videokeratography: Employ computed videokeratography to identify early keratoconus, corneal warpage, and asymmetrical or irregular astigmatism.[16]

Immediately before the SMILE procedure, a standard protocol involves instilling topical antibiotics and 0.5% topical proparacaine in both eyes. It is crucial to exercise caution and avoid excessive use of topical anesthetic, as overapplication may lead to the loosening of the corneal epithelium, potentially increasing the risk of complications such as the formation of black spots and epithelial defects.[7]

Technique or Treatment

The SMILE procedure involves several fundamental steps, such as docking, FS laser-assisted lenticule creation, lenticule dissection, and extraction. The refractive lenticule is separated from the stromal tissue through blunt dissection, initiated with a small side-cut incision. This dissection occurs first in the anterior plane, followed by the posterior plane.[1]

Patient Positioning, Counselling, and Preparation

Patient positioning is essential to the SMILE procedure to ensure comfort throughout. Thorough counseling and obtaining informed consent are prerequisites before initiating the procedure. For preoperative topical anesthesia, topical topical antibiotics and 0.5% topical proparacaine should be applied in both eyes.[7] As previously noted, care must be taken to avoid excess topical anesthetic, which could lead to complications such as the formation of black spots and epithelial defects by loosening the epithelium.

During the procedure, the patient's neck should not be twisted, and their legs should remain uncrossed. The patient should be instructed to take shallow breaths to minimize head movement. Proper head orientation is crucial for accurate docking and centration of the laser. Patients should be advised to remain calm, maintain fixation, and avoid squeezing the eye. Patient cooperation is of the utmost importance throughout the procedure.[10]

Docking

The patient should lie supine on the operating table, with the eye to be operated on positioned directly beneath the FS delivery system. Initial docking requires the use of a disposable curved contact glass. To ensure accurate positioning, the patient should adjust upwards so that the contact lens attaches precisely to the corneal surface, and the lens should adequately align with the corneal surface.[7] 

As the contact lens attaches to the cornea, a meniscus tear film will become visible, and the patient can easily see the fixation light as the vergence of the fixation beam is focussed per the patient's refraction. Verification of proper docking is crucial before initiating corneal contact with the contact glass interface. The patient is then instructed to fixate on a green blinking light for centration. Suction is initiated and maintained throughout the procedure.

The treatment pattern is centered on the coaxial sighted corneal light reflex (CSCLR), generated by a blinking green light over the cornea. Infrared light is used to confirm the centration of docking once the suction is activated, with a suction pressure of approximately 35 mmHg. Cyclotorsion compensation is manually adjusted after suction activation, particularly in cases with significant astigmatism.

The FS laser generates 4 sequential photoablation incisions, forming an intrastromal lenticule and a small 2.5 mm incision along the superior or superotemporal aspect of the cornea for lenticule access and extraction. The total time for the laser incisions ranges between 20 and 35 seconds, regardless of the magnitude of the refractive error. Subsequently, the surgeon may use a manual spatula to separate the residual lenticular appendages along the anterior and posterior planes, followed by forceps to extract the lenticule.[7] 

Femtosecond Laser Application

The FS laser parameters, setting, and lenticule and cap parameters can be customized based on the requirements and preferences of the surgeon, and they may vary from case to case (see Table. Cap and Lenticule Treatment Parameters). The treatment parameters for the anterior cap cut are typically set with a depth of 120 µm (within a range of 100 to 160 µm), a side cut width ranging from 2 to 5 mm, and a minimum lenticule thickness of 15 µm (within a range of 10 to 30 µm).

A 6 mm optical zone is maintained with no transition for spherical error, and a 0.1 transition zone is selected for astigmatism correction. The cap diameter is set 1 mm greater than the lenticule diameter. The pulse energy is adjusted between 100 and 160 nJ and varies among surgeons.[7] 

Table 3. Cap and Lenticule Treatment Parameters [7] 

In SMILE, the FS laser creates the intrastromal lenticule. The process involves an outside-in lenticule cut, followed by a lenticule side cut, and finally, a cap cut in an inside-out manner. The cap side cut is executed last in this procedure.

Lenticule Dissection

Following firing the FS laser, a thick, uniform bubble forms in the corneal stroma. Within this bubble, 2 rings become visible, corresponding to the diameter of the cap cut and the lenticule cut. These rings serve as landmarks, aiding in identifying the lenticule edge and guiding the necessary dissection. 

Subsequently, the cap side cut is opened entirely to its depth using a thin hook, and the lenticule edge is identified. The anterior and posterior lamellar tunnels are separated on the tunnel side, moving in opposite directions to prevent any inadvertent lenticule mis-dissection. Further, the lenticule edge is identified, and the anterior lenticule plane is separated from the overlying cap using a blunt lamellar dissector. The posterior plane is then dissected, leaving small peripheral areas undissected toward the corneal end to provide countertraction and prevent the lenticule from folding at 1 side.[7] 

Lenticule extraction poses a notable challenge for inexperienced surgeons, and incorrect identification of the tissue plane can result in adherence of the posterior lenticule surface to the stromal surface of the cap.[2] One method to discern the posterior plane during the formation of the posterior lamellar channel is the "meniscus sign," which refers to the meniscus-shaped gap between the inner ring and the lenticule edge.[7] 

In cases of improper lenticule dissection, distinguishing between the lenticule edge and the anterior dissection plane can be difficult as countertraction from the corneal stroma is lost. Various techniques have been described to facilitate the separation of the lenticule edge from the overlying cap. The "push-up" technique employs a Y-shaped tip to engage the lenticule edge and enhance it by pushing it up from the stromal bed.[7] Another option is using anterior segment optical coherence tomography (ASOCT), where dissection planes appear hyperreflective.[7] 

A newer method, termed "lenticuloschisis," allows for the direct peeling of the lenticule from the surrounding stroma and extraction without using a dissector. This technique has been suggested to result in a smooth interface, earlier visual recovery, and better visual quality in the immediate postoperative period due to minimal tissue manipulation.[1]

Occasionally, the lenticule may be retained in the stromal bed, presenting an intraoperative complication. In such cases, immediate resolution can involve converting to a FLEx procedure if the entire lenticule remains intact. Another option is customized surface ablation, which has limitations due to potential postoperative haze, which may result in suboptimal visual outcomes.[7] 

In the rare situation where lenticule extraction is not possible or a lenticule remnant is retained in the stromal bed postoperatively, irregular astigmatism may occur.[2] Effective treatment for this complication has been achieved through transepithelial phototherapeutic keratectomy (PTK).[1]

Medications typically administered during the postoperative period include topical steroids (dexamethasone 0.1%) and topical fluoroquinolone eye drops (moxifloxacin 0.5%) several times daily. Additionally, lubricating eye drops may be recommended for 1 to 2 weeks postoperatively. Close follow-up with the ophthalmologist is crucial in the weeks to months immediately following the SMILE procedure to monitor the healing process and address any potential issues or concerns that may arise.

Complications

Most intraoperative complications associated with SMILE are related to the steep learning curve and relative complexity of the procedure.[17] These complications can be broadly categorized into 3 main groups:

1. Lenticule creation
2. Lenticule dissection
3. Lenticule extraction.

Lenticule Creation

Complications related to lenticule creation include suction loss, the formation of an opaque bubble layer (OBL), subconjunctival hemorrhage, incisional bleeding, and black spots. Loss of suction, occurring in approximately 6% of cases, is typically due to patient eye contraction or sudden patient movement.[2][17] There is speculation that operating in the fast mode of the FS laser reduces the incidence of suction loss.[17] Management depends on when the complication occurs in surgery (see Table. Management for Suction Loss). If suction loss occurs when less than 10% of the lenticule has been cut, re-docking and re-centration are appropriate. If more than 10% of the lenticule has been cut, the procedure should convert to excimer laser ablation (PRK/LASIK), with most patients still achieving excellent visual outcomes.[7]

OBL, a result of bubble accumulation and opacification in the intrastromal interface, can be managed intraoperatively by massaging out bubbles. Although associated with delayed visual recovery, OBL generally results in good long-term visual outcomes.[7]

Black spots caused by debris or air bubbles entrapped between the contact lens and the cornea can be addressed by cleaning. They typically do not impact visual outcomes.[7]

Lenticule Dissection or Extraction 

Common lenticule dissection or extraction complications include lenticule remnants, corneal abrasions, lenticule adhesions, and incisional tears. Intraoperative or postoperative management, as described previously, can address lenticule remnants and adhesions. Peripheral corneal abrasions, occurring in 5.5% of cases, are typically due to excessive manipulation,[2][18] and may be inversely correlated with the surgeon’s expertise.[19]

Incisional tears, observed in 9.6% of patients, can result from surgeon inexperience or sudden eye movement during lenticule extraction. Preventative measures, such as manual fixation of the eye intraoperatively, may reduce the risk of incisional tears.[2] Both corneal abrasions and incisional tears can be managed postoperatively with artificial tears and a bandage contact lens, with minimal impact on visual outcomes.[18]

Primary complications experienced after SMILE include:[4]

• Dry eye
• Corneal abrasion
• Infectious keratitis

Postoperative dry eye occurs in approximately 3% of patients and is likely multifactorial, attributable to decreased trophic influence in the corneal epithelium, inflammation, damage to limbal goblet cells during suction, and impaired corneal sensation to blink.[2][20] Studies indicate lower dry eye symptoms following SMILE in the immediate postoperative period than FS-LASIK.[20] This finding has had quantitative verification through differences in tear film breakup, corneal sensitivity, and corneal nerve regeneration—all higher in SMILE than FS-LASIK.[1]

The incidence of infectious keratitis is reducible mainly by adhering to a postoperative topical antibiotic regimen. Prompt irrigation with bactericidal povidone-iodine and an antibiotic solution is recommended for patients with infectious keratitis.[18]

Other rare postoperative complications include epithelial ingrowth, irregular topography, micro striae, and interface inflammation.[2] All known instances of ectasia after SMILE were observed in eyes with diagnosed or undiagnosed forme fruste keratoconus.[3]

To sum up, the major complications after SMILE are as follows:

• Suction loss
• Black spots
• Opaque bubble layer
• Cap lenticular adhesions
• Retained lenticule
• Cap tears
• Side cut tears
• Epithelial defects 

Table 4. Management for Suction Loss [7] 

Signs to Identify the Cap Lenticule Adhesion

Cap lenticule adhesion during the SMILE procedure can be identified through various signs. These are discussed in further detail below.

Meniscus sign

The meniscus sign in SMILE is defined as the gap between the inner ring, representing the lenticule cut diameter, and the edge of the lenticule. This sign becomes evident when the surgeon slightly pushes the lenticule edge away while creating the posterior lamellar channel. Notably, the meniscus sign is observable exclusively during the posterior plane dissection and not during the anterior plane of dissection. The relation of the frilled lenticule edge with the instruments is a guide to identifying the dissection plane.[21]

Shimmer sign

During the dissection phase of SMILE, a notable bright light reflex is observed around the instrument. The reflex is not identifiable during the anterior plane of dissection but becomes apparent during the posterior plane dissection. The presence of this shimmer sign serves as a crucial indicator, aiding surgeons in accurately identifying the correct dissection plane.[22]

White ring sign

Enhancing the observation of the light reflex during SMILE is achieved by employing oblique external illumination, particularly in the presence of a dark iris. The white ring position in relation to the instrument helps to identify the dissection plane as the white ring is posterior to the instrument during the anterior plane dissection and anterior to the posterior plane of dissection.[23]

Stop sign

The stop sign phenomenon in SMILE surgery refers to the resistance encountered at the junction of the dissected and undissected halves of both planes, impeding the lateral movement of surgical instruments. This distinctive resistance serves as a tactile guide, aiding surgeons in delineating the correct anterior and posterior lenticular planes during the dissection phase of the procedure. The resistance is perceptible at both the anterior and posterior lenticular planes. Identifying the stop sign facilitates the precise dissection of the lenticule from the cap above and the underlying stroma, minimizing the risk of complications arising from incorrect tissue dissection.[24]

Clinical Significance

Numerous meta-analyses have demonstrated that SMILE exhibits comparable long-term efficacy, predictability, and safety outcomes to FS-LASIK.[2][25] A recent multicenter study demonstrated that 88% and 98% of eyes achieved a correction within +/- 0.5 and +/- 1 D of the targeted correction at 3 months postoperatively.[26] Additional studies have reported that 61% to 96% of patients achieve a long-term uncorrected distance visual acuity (UDVA) of 20/20 or better.[1]

Current research suggests several benefits of SMILE compared to FS-LASIK. Clinical trials have demonstrated a reduction in postoperative dry eye associated with SMILE than LASIK.[20] SMILE has been associated with significantly fewer HOAs,[2] possibly due to a more uniform corneal refractive power.[8] Moreover, fewer inflammatory cells in corneas following SMILE have been found than those after FS-LASIK.[2]

Patients undergoing SMILE tend to exhibit higher satisfaction levels and an improved vision-related quality of life compared to LASIK recipients.[27][28] SMILE has been demonstrated to result in less severe denervation and accelerated neuronal healias compared to FS-LASIK.[2] Recent studies support the notion that SMILE provides superior corneal biomechanical stability than FS-LASIK, as evidenced by corneal hysteresis and corneal resistance factor measurements.[1][2] Despite these promising findings, given that SMILE is a relatively recent development in laser refractive surgery, further clinical trials are warranted to validate and substantiate the proposed advantages of SMILE over FS-LASIK.

While SMILE presents several advantages, there are also considerations and drawbacks compared to FS-LASIK. Patients undergoing SMILE may experience higher reported discomfort during tissue manipulation than flap lifting in LASIK. To address this, inexperienced surgeons should consider administering additional topical anesthesia or prescribing anxiolytics or sedatives before surgery.[28] Light sensitivity and blurred vision issues at 1 month postoperatively are more frequently reported by patients who undergo SMIL than those who undergo FS-LASIK. However, these concerns tend to resolve as early as 3 months postoperatively.[28] Visual recovery may be slower with SMILE compared to FS-LASIK. At 3 months postoperatively, there may be more backscatter in eyes treated with SMILE, though no significant difference is observed at 6 months postoperatively.[1][2]

Notably, SMILE has demonstrated slightly inferior outcomes in treating low-to-moderate astigmatism than LASIK but comparable results in correcting high astigmatism.[8][29] Undercorrection occurs in 11% of patients with astigmatism who undergo SMILE, likely due to the lack of cyclotorsion control or eye-tracking technology in the Visumax platform.[2][30] To address this limitation, some experts recommend the preoperative placement of limbal marks at 0° and 180° on the cornea while the patient is in a seated position. When the patient is supine during the procedure, these marks can help indicate the degree of cyclotorsion and aid in more precise astigmatism correction.[8]

While most patients undergoing SMILE express satisfaction with their long-term visual outcomes, approximately 3% undergo enhancement procedures within 2 years of the initial procedure.[31] Risk factors for enhancement include older age, greater preoperative myopia, higher preoperative astigmatism, and intraoperative loss of suction.[8] Retreatment is far more likely to occur due to under-correction rather than overcorrection.[31] Given that a significant proportion of patients undergoing SMILE may experience impaired corrected distance visual acuity (CDVA) up to 3 months postoperatively, the decision to perform enhancement procedures should be delayed to allow sufficient time to recover visual function.[2]

The optimal procedure for retreatment after SMILE remains a subject of debate, with various options proposed. These include repeat SMILE below the cap, surface ablation (PRK) augmented by mitomycin-C (MMC), thin-flap LASIK in the cap, and cap-to-flap (also known as the CIRCLE approach).[2]

Repeat SMILE lacks robust data supporting its efficacy and safety, with some authors advising against it due to the risk of creating multiple dissection planes.[7] While avoiding flap formation and preserving biomechanical strength, surface ablation with MMC is associated with increased postoperative pain and slower visual recovery.[32] Thin-flap LASIK, though easy to perform with minimal postoperative pain, poses a risk of flap-related complications, and its efficacy and safety in SMILE retreatment lacks extensive data. Some authors have suggested that thin-flap LASIK may be suitable only for patients with cap thickness over 135 µm and low refractive error.[32] Lastly, the CIRCLE approach, where the SMILE cap converts into a full flap, offers minimal pain and rapid recovery with significant data to support its efficacy and safety; however, this method carries the risk of flap-related complications and is relatively difficult to perform.[32]

Recent developments indicate a potential expansion of SMILE applications, particularly in treating hyperopia. Limited research has suggested that SMILE yields comparable visual outcomes, recovery rate, and safety outcomes as hyperopic LASIK [4] with the added benefit of reduced postoperative inflammation. However, until SMILE receives FDA approval for hyperopia treatment, comprehensive long-term safety and efficacy data remain unavailable, especially compared to other laser refractive procedures.[1]

Additionally, 2 lenticule implantation techniques, lenticule intrastromal keratoplasty (LIKE) and small incision lenticule intrastromal keratoplasty (sLIKE) have been introduced for treating high hyperopia. A minus lenticule is centrally placed on the optical axis within a stromal pocket in these procedures. A pilot study of 10 eyes that underwent LIKE resulted in 90% within +/- 1 D of target refraction at 6 months. The small incision variant, sLIKE, is anticipated to offer advantages such as minimized injury to the subbasal nerve plexus, enhanced corneal strength, and a reduced risk of flap-related complications.[4] Further trials are warranted to evaluate the efficacy and safety of these 2 procedures.

Ongoing research explores the integration of SMILE with accelerated corneal cross-linking (CXL), also known as SMILE XTRA. This technique involves the intraoperative injection and application of 0.25% riboflavin in the stromal interface for 1 minute, followed by 75 seconds of UV-A radiation exposure. This procedure is hypothesized to improve the accessibility of laser refractive surgery to individuals with thin corneas at baseline by minimizing the risk of postoperative ectasia. Recent trials on SMILE XTRA have shown promise, but the long-term effects still need to be evaluated.[1]

Enhancing Healthcare Team Outcomes

A comprehensive and effective approach to SMILE involves an interprofessional team of ophthalmic surgeons, nurses, optometrists, and technicians. This collaborative effort spans the preoperative evaluation, surgery, and postoperative management phases. Patient selection, adhering to established guidelines, is critical for optimizing long-term visual outcomes and ensuring patient satisfaction.

Nurses play a crucial role in the surgical setting by assisting during the procedure and providing postoperative care. Their responsibilities extend to ensuring patient compliance, addressing queries, and offering support during recovery. The interprofessional healthcare team should collectively maintain vigilance for clinical signs and symptoms indicative of major postoperative complications. In such complications, a prompt referral to a cornea specialist is imperative.[33]

This interprofessional collaboration, marked by each member's specialized contributions, enhances the overall quality of care throughout the SMILE surgery process. Effective communication and coordination among team members are essential to delivering optimal outcomes and ensuring a positive patient experience.

Nursing, Allied Health, and Interprofessional Team Interventions

Nurses play a vital role in the SMILE surgical process, contributing to patient care and safety. Nurses should ensure that the patient has signed the necessary consent forms, which involves confirming the patient's understanding of the procedure's risks and obtaining informed consent.

While SMILE is a relatively short-duration procedure, continuous monitoring by a nurse is essential. Monitoring includes tracking vital signs, ensuring patient comfort, and addressing immediate concerns during the surgery. Maintaining a calm and reassuring environment is crucial during the procedure. Nurses are pivotal in alleviating unnecessary anxiety, offering support, and keeping the patient at ease throughout the surgical process.

After the SMILE surgery, nurses continue to monitor the patient for a few hours before discharge.[34] This involves assessing postoperative recovery, checking for any signs of discomfort, and ensuring the patient is ready for discharge.

Nursing, Allied Health, and Interprofessional Team Monitoring

The interprofessional team plays a crucial role in monitoring patients throughout the SMILE surgical process. In the preoperative phase, a collaborative team, including ophthalmic surgeons, nurses, optometrists, and technicians, conducts a thorough evaluation to assess patient suitability based on established guidelines. The team ensures that appropriate patient selection is maintained, emphasizing adherence to safety protocols. This interprofessional collaboration continues into the surgical phase, where nurses assist during the procedure, providing essential support and ensuring the patient's comfort. Postoperatively, nurses are instrumental in delivering care, monitoring patients for any signs of complications, and addressing concerns.

Patients should receive proper guidance for a successful recovery. Before discharge, nurses emphasize essential postoperative instructions to enhance patient understanding. The significance of attending scheduled follow-up appointments with the ophthalmologist is stressed, as these visits allow the healthcare team to monitor recovery progress closely. Emphasizing eye protection, nurses recommend using eye coverings during sleep to prevent accidental contact and scratching of the eyes. Additionally, patients are advised to wear eyeglasses outdoors during the initial week post-surgery, providing an extra layer of protection for the healing cornea.[34]