LASIK

LASIK Basics - Laser Sharp Vision

• LASIK: Laser-Assisted In Situ Keratomileusis.
• Principle: Excimer laser photoablates corneal stroma under a flap, reshaping cornea for vision correction.
• Lasers Used:
  • Flap Creation: Femtosecond laser.
  • Stromal Ablation: Excimer laser (193nm ArF).
• Advantages vs. PRK: Faster visual recovery, ↓ post-op pain, less haze.

⭐ Excimer laser (193nm ArF) causes photoablative decomposition, breaking C-C bonds in corneal stroma with minimal thermal damage. oka

LASIK Candidacy - Perfect Peepers?

• Indications: Myopia (≤-10D), Hyperopia (≤+4D), Astigmatism (≤4-5D).
• Criteria: Age >18-21 years; stable refraction for ≥1 year.
• Absolute Contraindications: Keratoconus, active corneal disease, uncontrolled autoimmune disease, pregnancy/lactation, unrealistic expectations.
• Relative Contraindications: Thin corneas (Residual Stromal Bed - RSB critical), severe dry eyes, large pupils, glaucoma, poorly controlled diabetes.
• 📌 Mnemonic (Contraindications): K SOAP (Keratoconus, Systemic, Ocular surface, Age/Amblyopia, Psychological/Pregnancy).

⭐ Minimum Residual Stromal Bed (RSB) of 250-300 µm (ideally >300µm) is crucial post-ablation to prevent iatrogenic keratectasia.

LASIK Pre-Op - Measuring Up

• History: Detailed ocular & medical.
• Visual Acuity: Uncorrected (UCVA) & Best-Corrected (BCVA).
• Refraction: Manifest & Cycloplegic (crucial for latent hyperopia, myopic overcorrection).
• Corneal Assessment: Topography/Tomography (e.g., Pentacam) to rule out keratoconus/forme fruste.
• Pachymetry: Central Corneal Thickness (CCT); average 530-550 µm.
• Pupillometry: Scotopic pupil size (risk for night vision issues).
• Tear Film & IOP: Schirmer's, TBUT; Intraocular pressure.

⭐ Corneal topography/tomography is essential to rule out keratoconus and forme fruste keratoconus, absolute contraindications for LASIK surgery.

LASIK Procedure - Flap & Zap Dance

• Anesthesia: Topical anesthetic drops (e.g., Proparacaine).
• 1. Corneal Flap Creation ("Flap"):
  • Methods: Mechanical microkeratome (blade) or Femtosecond laser (bladeless).
  • Flap Thickness: 90-160 µm.
• 2. Stromal Ablation ("Zap"):
  • Laser: Excimer (193 nm Argon Fluoride).
  • Action: Reshapes corneal stroma based on pre-operative calculations.
  • Precision: Eye tracking systems active.
• 3. Flap Repositioning:
  • Careful alignment and adherence of flap (sutureless).
  • Interface irrigation performed.

⭐ Femtosecond lasers create more precise, planar flaps with customizable hinge position and side-cut angles compared to mechanical microkeratomes.

LASIK Complications & Post-Op - Healing Hurdles

• Post-Op Care:
  • Meds: Topical antibiotic (Moxifloxacin), steroid (Prednisolone acetate), lubricants. Eye shield nightly.
  • Early Symptoms: FB sensation, photophobia, tearing, mild pain, transient fluctuating vision.
• Complications: 📌 FADE IN (Flap issues, DLK, Ectasia, Infection, Neurotrophic Keratopathy/Dry Eye)
  • Intra-op: Flap (buttonhole, free cap, incomplete, thin).
  • Early Post-op: Flap dislocation/striae, DLK ('Sands of Sahara'), infection (rare), epithelial ingrowth.
  • Late Post-op: Corneal ectasia (most feared; risk: thin RSB, poor topography), regression, chronic dry eye, night vision issues.

  ⭐ Diffuse Lamellar Keratitis (DLK), 'Sands of Sahara,' non-infectious interface inflammation. Grade 1-2: topical steroids. Grade 3-4: flap lift/irrigation.

High‑Yield Points - ⚡ Biggest Takeaways

• LASIK: Excimer laser (193nm ArF) ablates stroma under a corneal flap.
• Flap created by microkeratome or femtosecond laser.
• Corrects myopia, hyperopia, and astigmatism.
• Contraindications: Thin cornea (<500µm pre-op), Residual Stromal Bed (RSB) <250µm, keratoconus, unstable refraction.
• Most common complication: Dry eyes. Serious: DLK, epithelial ingrowth, corneal ectasia.
• Minimum age 18 years; refraction stable for >1 year.