Laser vision correction procedures have evolved significantly over the past few decades. Small Incision Lenticule Extraction (SMILE) represents the third generation of this refractive surgery technology. This modern, minimally invasive approach aims to correct common vision issues like nearsightedness.
Understanding Small Incision Lenticule Extraction
SMILE stands for Small Incision Lenticule Extraction. The procedure differs from predecessors because it uses only a single femtosecond laser to perform the entire correction without creating a large hinged flap on the cornea’s surface. This advanced technology creates a precise, disc-shaped piece of tissue, known as a lenticule, within the intact layers of the cornea.
The lenticule is custom-shaped based on the patient’s specific refractive error. This tissue is thicker at the center and becomes thinner toward its edges, similar to a miniature contact lens carved inside the eye. The laser also creates a tiny access tunnel, typically measuring between two and four millimeters, through which the lenticule is subsequently removed.
The Step-by-Step SMILE Procedure
The SMILE process begins after the eye is numbed with topical anesthetic drops and stabilized with a suction ring. The femtosecond laser focuses its energy within the corneal stroma. This laser delivers rapid, ultra-short pulses to create thousands of microscopic bubbles that outline the shape of the corrective lenticule.
This creation process involves two primary cuts: one defining the posterior surface of the lenticule and a second defining the anterior surface, or the cap. The entire laser application is quick, often taking less than 30 seconds to complete the cutting of both the lenticule and the small access incision.
Next, the surgeon uses fine instruments to carefully separate and dissect the lenticule from the surrounding corneal tissue through the small incision. The surgeon then extracts the detached lenticule through this small keyhole opening.
The physical removal of the lenticule immediately changes the curvature and shape of the cornea. By precisely flattening the central cornea, light entering the eye is correctly focused onto the retina, correcting the patient’s nearsightedness. The small incision naturally self-seals quickly, allowing the cornea to maintain its structural integrity.
Candidacy Requirements
SMILE surgery is primarily approved for the treatment of myopia (nearsightedness) and myopic astigmatism. Candidates must be at least 18 years old, though some centers prefer a minimum age of 22 to ensure full eye maturity. A prerequisite is a stable prescription, meaning the refractive error has not changed significantly (less than 0.5 diopters) for at least twelve months.
The procedure is effective for correcting myopia between -1.00 and -10.00 diopters, and astigmatism up to -3.00 to -5.00 diopters. Patients are typically ineligible if they have:
- Extremely thin corneas.
- Severe dry eye syndrome.
- Certain systemic conditions like uncontrolled diabetes or autoimmune disorders.
- Other eye diseases, such as cataracts or advanced glaucoma.
SMILE Versus Traditional Laser Eye Surgery
The core difference between SMILE and traditional laser-assisted in situ keratomileusis (LASIK) lies in the method of accessing the corneal tissue. LASIK requires the creation of a large, hinged corneal flap to expose the underlying tissue for reshaping with a second excimer laser. SMILE entirely bypasses this flap creation, requiring only the two-to-four-millimeter incision for lenticule extraction.
Because SMILE avoids the large flap, the upper corneal layers remain largely intact, which helps preserve the biomechanical stability of the cornea. The smaller incision also results in less disruption to the corneal nerves, leading to a lower incidence and severity of post-operative dry eye symptoms compared to LASIK.
While LASIK often provides instant visual recovery, the recovery with SMILE is slightly more gradual, often taking a day or two to achieve functional vision. However, the flapless nature of SMILE makes it a preferred option for individuals with highly active lifestyles or professions where there is a risk of eye trauma, as there is no possibility of flap displacement. Both procedures offer excellent long-term visual outcomes.