Small Incision Lenticule Extraction

Introduction

Small Incision Lenticule Extraction (SMILE) is a refractive surgical procedure used to correct myopia (nearsightedness) and astigmatism. It is a minimally invasive technique that utilizes a femtosecond laser to create a lenticule within the corneal stroma, which is then extracted through a small incision. This procedure is considered an advancement over traditional laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) due to its reduced impact on corneal biomechanics and faster recovery times.

Historical Background

The development of SMILE can be traced back to the early 2000s when researchers sought alternatives to LASIK that would minimize complications associated with flap creation. The introduction of femtosecond laser technology paved the way for the evolution of SMILE. In 2007, the first SMILE procedure was performed, and it received CE approval in Europe in 2011. Since then, SMILE has gained popularity worldwide, with ongoing research and improvements enhancing its efficacy and safety.

Procedure Overview

The SMILE procedure involves several key steps:

1. **Preoperative Assessment**: Patients undergo a comprehensive eye examination to determine their suitability for SMILE. This includes measuring corneal thickness, refractive error, and overall eye health.

2. **Lenticule Creation**: A femtosecond laser is used to create a precise lenticule within the corneal stroma. The laser also forms a small incision, typically 2-4 mm, through which the lenticule will be extracted.

3. **Lenticule Extraction**: The surgeon carefully extracts the lenticule through the incision, reshaping the cornea to correct the refractive error.

4. **Postoperative Care**: Patients are monitored for complications and are prescribed medications to aid healing and prevent infection.

Advantages of SMILE

SMILE offers several advantages over traditional refractive surgeries:

- **Minimally Invasive**: The absence of a corneal flap reduces the risk of flap-related complications and preserves corneal integrity. - **Faster Recovery**: Patients typically experience quicker visual recovery and less postoperative discomfort compared to LASIK. - **Reduced Dry Eye Incidence**: The smaller incision and lack of flap creation result in less disruption to corneal nerves, reducing the incidence of dry eye symptoms. - **Stability**: SMILE provides stable refractive outcomes with a lower risk of regression.

Indications and Contraindications

SMILE is primarily indicated for the correction of myopia and myopic astigmatism. Ideal candidates are those with stable refractive errors, adequate corneal thickness, and no contraindications such as keratoconus or severe dry eye syndrome. Patients with thin corneas or those involved in contact sports may benefit from SMILE due to its minimally invasive nature.

Contraindications include:

- **Keratoconus**: A progressive thinning disorder of the cornea. - **Severe Dry Eye**: Can be exacerbated by refractive surgery. - **Autoimmune Disorders**: May affect healing. - **Pregnancy**: Hormonal changes can affect refractive stability.

Complications and Management

While SMILE is generally safe, potential complications include:

- **Infection**: Rare but can occur if postoperative care is not followed. - **Epithelial Ingrowth**: Occurs when epithelial cells grow into the corneal stroma. - **Residual Refractive Error**: May require enhancement procedures. - **Corneal Haze**: Transient and usually resolves with medication.

Management of complications involves prompt diagnosis and treatment, often with medications or additional surgical interventions.

Comparison with Other Refractive Surgeries

SMILE is often compared to LASIK and PRK:

- **LASIK**: Involves creating a corneal flap, which can lead to flap-related complications. Recovery is faster than PRK but slower than SMILE. - **PRK**: No flap is created, making it suitable for patients with thin corneas. However, recovery is longer, and there is more postoperative discomfort compared to SMILE.

Future Directions and Research

Ongoing research aims to expand the indications for SMILE, including hyperopia and presbyopia. Advances in laser technology and surgical techniques continue to improve the precision and outcomes of SMILE. Long-term studies are being conducted to assess the stability and safety of SMILE over decades.