SMILE — Small Incision Lenticule Extraction — is the most significant innovation in corneal refractive surgery since LASIK replaced PRK in the 1990s. Flapless, minimally invasive, and associated with less post-surgical dry eye than LASIK, SMILE has earned a substantial and growing share of the refractive surgery market since its FDA approval in the United States in 2016.
This guide provides a complete, clinical overview of SMILE — how it works, who it is for, how it compares to LASIK, and what the latest evidence says about outcomes and long-term stability. It is part of the Vision Correction Procedures Compared hub.
How SMILE Works
SMILE is unique in refractive surgery because it requires only a single laser — a femtosecond laser — to perform the entire procedure. LASIK uses two lasers (femtosecond to create the flap, excimer to ablate). PRK uses one laser (excimer). SMILE uses only the femtosecond.
Step-by-step procedure:
1. Suction coupling: The patient fixes on a blinking target while a low-pressure suction device gently holds the eye still. This is the most unusual sensation of the procedure — a brief feeling of pressure and dimming of vision.
2. Lenticule creation: The femtosecond laser fires thousands of ultrashort pulses inside the corneal stroma, creating two curved cuts at precise depths. The tissue between these cuts — called the lenticule — is a small, disc-shaped piece of cornea calculated to produce the desired refractive correction when removed.
3. Cap incision: The laser creates a small arcuate incision through the corneal surface, 2–4mm in length (compared to a 20mm flap edge for LASIK).
4. Lenticule dissection and extraction: The surgeon uses a blunt dissector to separate the lenticule from the surrounding stromal tissue and extracts it through the small incision.
5. Completion: The incision seals naturally. No flap is created. No sutures are required.
The entire procedure takes approximately 20–25 minutes per eye, slightly longer than LASIK (15–20 minutes) but comparable to PRK.
What SMILE Treats
SMILE’s FDA approval covers:
- Myopia: -1.00D to -10.00D
- Astigmatism: -0.75D to -3.00D (concurrent with myopia)
SMILE does not treat hyperopia (farsightedness). This is its most significant treatment range limitation compared to LASIK, which treats hyperopia up to +6.00D.
Beyond FDA-approved parameters, some surgeons and international markets are evaluating extended SMILE parameters, but the data outside the approved range are less mature.
How SMILE Compares to LASIK
Optical Outcomes
For myopia within SMILE’s approved range, the refractive outcomes are equivalent to LASIK. Large prospective studies and randomized controlled trials consistently show similar rates of patients achieving 20/20 or better (96–98%), similar residual prescription accuracy, and similar patient satisfaction.
One nuance: early SMILE outcomes (at one week and one month) may lag slightly behind LASIK due to differences in early healing. By three months, outcomes converge.
Dry Eye
The most clinically significant advantage SMILE holds over LASIK is a substantially lower rate and severity of post-surgical dry eye. The mechanism is well-understood: LASIK creates a full-sized corneal flap, which severs virtually all anterior corneal nerve branches running beneath the flap. This nerve disruption reduces tear production and corneal sensation for 3–12 months.
SMILE’s small 2–4mm incision disrupts only the nerve branches in that small zone. The vast majority of anterior stromal nerves remain intact. Multiple studies have confirmed that SMILE patients have significantly better tear break-up times, less dry eye symptom burden, and faster recovery of corneal sensitivity compared to LASIK patients at equivalent follow-up periods.
For patients with borderline dry eye, SMILE is meaningfully preferable to LASIK. For patients with established moderate-to-severe dry eye, EVO ICL remains the preferred non-corneal-altering option.
Corneal Biomechanics
The cornea’s structural integrity is better preserved in SMILE than in LASIK. LASIK’s flap cuts through the mechanically important anterior Bowman’s layer across a large circular area. SMILE’s small incision through the cap leaves Bowman’s layer essentially intact across the anterior cornea. This biomechanical advantage is supported by corneal hysteresis and topographic stability data, though clinical differences in practice are modest for most patients within typical treatment ranges.
No Flap Risk
LASIK’s corneal flap introduces a small but permanent risk: the flap can be traumatically dislodged by a direct blow to the eye — even years after surgery. SMILE patients carry no such risk. For contact athletes, military personnel, or anyone with a lifestyle involving regular facial trauma risk, SMILE’s flapless design is a meaningful practical advantage.
Treatment Range
LASIK has the broader FDA-approved range — including hyperopia, and a higher maximum myopia in some platforms. For patients with hyperopia or very high myopia (above -10.00D), LASIK or EVO ICL remains the appropriate choice.
SMILE vs PRK
SMILE and PRK both avoid the flap, but they differ significantly in recovery. PRK requires 5–7 days of significant discomfort and 2–4 weeks of blurred vision during epithelial healing. SMILE provides LASIK-like recovery speed — functional vision within 24–48 hours — with PRK-like biomechanical and dry-eye benefits. For most patients within SMILE’s approved range who want flapless surgery without PRK’s recovery burden, SMILE is the superior choice.
The VISUMAX Laser Platform
SMILE is performed exclusively on Carl Zeiss Meditec’s VISUMAX femtosecond laser. The original VISUMAX 500 has been succeeded by the VISUMAX 800, which features:
- Faster pulse repetition rate (2 MHz vs. 500 kHz), reducing procedure time
- Improved software for astigmatism treatment accuracy
- Enhanced alignment aids for toric corrections
- A smaller, more comfortable suction interface
In the US market, not every refractive surgery center has invested in the VISUMAX 800. Confirming which platform generation your surgeon uses is a reasonable quality question.
Candidacy Requirements
Ideal SMILE candidates share the following characteristics:
Prescription: Myopia -1.00D to -10.00D, with or without astigmatism up to -3.00D.
Corneal thickness: Similar to LASIK requirements. Adequate residual stromal bed after lenticule removal. Typically requires central corneal thickness of 480+ microns.
Age: 18 or older with stable prescription (no significant change for at least 2 years).
Dry eye: SMILE is a good option for patients with mild dry eye who would otherwise be borderline for LASIK. For moderate-to-severe dry eye, EVO ICL remains preferable.
Not a SMILE candidate if:
- Hyperopia is the primary error
- Astigmatism exceeds -3.00D
- Myopia exceeds -10.00D
- Keratoconus or other corneal ectatic disease
- Insufficient anterior chamber depth (this is relevant for EVO ICL screening, not SMILE, but worth mentioning for completeness)
What to Expect: Recovery
SMILE recovery is comparable to LASIK in timeline. Most patients experience:
- Day 1: Functional vision with mild haziness. Scratchiness and light sensitivity are modest, significantly less than PRK.
- Week 1: Vision continues improving. Halos at night are common and diminish over weeks.
- Month 1: Full visual stability for most patients.
- Dry eye symptoms: Minimal, peaking in week 1–2 and typically resolving faster than LASIK dry eye.
Activity restrictions are similar to LASIK — no swimming for 2 weeks, no contact sports for 2–4 weeks.
Enhancing SMILE Outcomes
Because SMILE does not use an excimer laser, retreatment of residual refractive error after SMILE requires either:
- Surface ablation (PRK) over the treated area — straightforward in most cases
- LASIK enhancement — can be performed by creating a LASIK flap over the SMILE cap, though this technique requires specific surgical expertise
Enhancement rates for SMILE are similar to LASIK: approximately 2–5% within five years.
Related Resources
- LASIK vs PRK vs EVO ICL: Complete Comparison
- Recovery Comparison: LASIK, PRK, and EVO ICL
- Vision Correction Procedures Compared
- What Is SMILE Eye Surgery and How Does It Compare?
- Can I Get Vision Correction If I Have Dry Eyes?
- Which Vision Correction Procedure Is Best for Athletes?
- What Are the Newest Vision Correction Technologies?
*This content is educational and does not constitute medical advice. All surgical decisions should be based on a comprehensive pre-operative evaluation with a qualified ophthalmologist.*