Small Incision Lenticule Extraction

SMILE Basics - Laser Precision Peeks

• Definition: Small Incision Lenticule Extraction (SMILE) is a minimally invasive, all-femtosecond laser refractive surgery.
• Principle: A femtosecond laser creates an intrastromal lenticule (reshaping cornea), extracted via a small 2-4 mm incision.
• Laser: Typically VisuMax femtosecond laser.
  • Wavelength: ~$1043 \text{ nm}$.
  • Parameters: Low pulse energy, high pulse frequency, precise small spot size.

⭐ SMILE aims to combine PRK's flapless advantage with LASIK's minimal discomfort and rapid visual recovery.

Patient Selection - Ideal Eyes Only

Indications:

• Myopia: -0.50 D to -10.00 D
• Astigmatism: ≤ -5.00 D
• Stable refraction (≥1 yr)
• Age ≥18 yrs

Contraindications:

• Absolute: Keratoconus, ectasia, active infection, uncontrolled autoimmune disease.
• Relative: Thin corneas (e.g., CCT < 480 µm, planned RSB < 250-300 µm), severe DED, pregnancy, unrealistic expectations.

Pre-op Workup:

• Refraction (M & C)
• Corneal topography/tomography (Pachy, K-vals, ectasia screen)
• Scotopic pupil size
• Dry eye eval (TBUT, Schirmer)

⭐ Crucial for stability: minimum post-SMILE Residual Stromal Bed (RSB) thickness, typically > 250-300 µm.

Surgical Steps - The Micro-Incision Magic

Key stages:

• Patient Preparation: Topical anesthesia, sterile draping.
• Docking: Interface cone, patient fixation, centration.
• Laser Application (Femtosecond): 📌 Dock, Laser, Dissect, Extract (DLDE)
  • 1. Posterior lenticule surface scan (refractive cut).
  • 2. Anterior lenticule surface scan (cap cut, thickness 100-160 µm).
  • 3. Side cuts for small incision(s) (e.g., 2-4 mm).
• Lenticule Dissection: Manual separation of lenticule from overlying cap and underlying stroma.
• Lenticule Extraction: Gentle removal through the micro-incision.

⭐ The cap in SMILE remains largely intact, contributing to better biomechanical stability and potentially less dry eye compared to a LASIK flap.

SMILE vs Others - The Refractive Rumble

• SMILE Disadvantages: Higher learning curve; enhancements challenging (surface ablation/conversion to LASIK); limited for hyperopia (evolving).

⭐ SMILE is associated with a lower incidence and severity of post-operative dry eye compared to LASIK due to preservation of anterior corneal nerves.

Complications & Care - Smooth Healing Guide

• Intraoperative:
  • Suction loss (may convert to LASIK/PRK), Opaque Bubble Layer (OBL), cap tear, difficult lenticule extraction, retained fragments.
• Postoperative:
  • Early: Interface inflammation (DLK-like), dry eye, transient light sensitivity.
  • Late: Haze, epithelial ingrowth (rare), infection (rare), refractive errors (under/overcorrection, irregular astigmatism).
• Management: Tailored to specific issue; e.g., topical steroids for interface inflammation.
• Post-op Care: Topical antibiotics, steroids, lubricants. Regular follow-up visits.

⭐ Suction loss during SMILE is a critical intraoperative complication that may necessitate conversion to another procedure like LASIK or PRK for completion of refractive correction.

High‑Yield Points - ⚡ Biggest Takeaways

• SMILE is a flapless procedure using only a femtosecond laser.
• Corrects myopia (up to -10D) and astigmatism (up to -5D).
• Involves creating and extracting an intrastromal lenticule via a small incision (<4mm).
• Offers superior corneal biomechanical strength preservation compared to LASIK.
• Results in less dry eye and corneal nerve damage than LASIK.
• A single laser platform (femtosecond) is used for the entire procedure.
• Currently not suitable for hyperopia correction or mixed astigmatism treatment alone.