LASIK (Laser-Assisted In Situ Keratomileusis)

What It Is

How It Corrects Vision

• Myopia: up to -6 to -8 D
• Hypermetropia: up to +3 to +4 D
• Astigmatism: up to 5 D (depending on corneal thickness)

Preoperative Evaluation

• Complete ocular examination (refraction must be stable for at least 1 year)
• Tear film osmolarity - to exclude dry eye syndrome
• Corneal pachymetry - to measure thickness and detect mild keratoconus
• Corneal topography - to exclude irregular astigmatism, keratoconus, and forme fruste keratoconus
• Corneal OCT - to produce an epithelial map
• Wavefront aberrometry (corneal and whole eye)
• Contact lens wearers: soft lenses discontinued for 2 weeks, rigid/gas-permeable lenses for at least 3 weeks before examination

Surgical Technique (Step by Step)

1. Patient positioning - Supine position; fellow eye taped closed; operative eye held open with a speculum.
2. Anesthesia - Topical anesthetic eye drops applied.
3. Suction ring application - A suction ring is centered on the cornea, substantially raising intraocular pressure. This stabilizes the eye and provides a guide track.
4. Flap creation - A thin corneal flap (including epithelium, Bowman's membrane, and superficial stroma) is created in one of two ways:
   • Mechanical microkeratome - An oscillating blade advances across the cornea
   • Femtosecond laser (now preferred) - Infrared laser pulses create microcavitation bubbles in a precise cleavage plane, producing a flap of uniform thickness (100-120 µm). Significantly reduces flap-related intraoperative complications.
5. Flap reflection - The hinged flap is folded back to expose the underlying stromal bed.
6. Excimer laser ablation - The stroma is reshaped by the excimer laser (wavelength 193 nm, UV range) with negligible disruption to surrounding tissue.
7. Flap repositioning - The flap is carefully replaced over the stromal bed. It adheres naturally - no sutures required.
8. Post-op assessment - The flap interface and centration are confirmed.

Variations

• Wavefront-guided LASIK - Excimer laser uses a custom ablation pattern based on whole-eye wavefront aberrometry measurements to reduce post-op higher-order aberrations.
• "Optimised" LASIK - Uses a specific ablation algorithm to create larger optical zones and better corneal asphericity, reducing night glare.
• LASIK Plus (LASIK + Cross-linking) - Riboflavin is applied to the stromal bed before flap replacement, followed by UV light exposure after repositioning. Considered for patients at risk of ectasia or refractive regression (usually >-7 D).

Contraindications

• Refractive instability (>0.5 D change in the last year)
• Corneal ectasia or keratoconus
• Residual corneal bed < 250 µm after planned ablation
• Uncontrolled diabetes mellitus
• Pregnancy/nursing

• Severe dry eye
• Thin corneas
• High refractive errors outside treatable range (intraocular procedure preferred instead)
• Occupations/activities with high eye trauma risk (flap dislocation risk)

Advantages Over Surface Ablation (PRK)

• Greater postoperative comfort
• Faster visual rehabilitation
• More rapid stabilization of refraction
• Milder stromal haze
• Can treat a wider range of refractive errors

Intraoperative Complications

• Buttonholing - Microkeratome penetrates through the flap (rare with femtosecond laser)
• Flap amputation - Incomplete hinge (rare)
• Irregular flap creation
• Anterior chamber penetration (very rare)

Postoperative Complications

Early (within 2 weeks)

Late (weeks to months)

Postoperative Care

• Topical antibiotics and steroids for the first 1-4 weeks
• Artificial tears for dry eye management
• Avoid eye rubbing (flap disruption risk)
• Follow-up at day 1, week 1, 1 month, and 3 months
• Final refraction usually stable by 3 months

Comparison: LASIK vs. PRK vs. SMILE