Surgery

Laser In-Situ Keratomileusis

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Laser In-Situ Keratomileusis, LASIK

  • Indication
  1. Refractive Surgery to Correct Refractive Error
  2. Current Refractive Surgery procedure of choice
    1. Replaces Photorefractive Keratectomy (PRK)
    2. Replaces Radial Keratotomy (RK)
  • Criteria
  • LASIK (and PRK)
  1. Age 18 years or older
  2. Stable Refraction for at least 1 year
  3. Myopia -0.50 to -12 diopters
  4. Hyperopia less than +0.50 to +6 diopters
  5. Astigmatism less than or equal to 5 diopters
  6. Adequate Corneal thickness
  7. No contraindications below
  • Contraindications
  1. Corneal disease
    1. Keratoconus
    2. Corneal Scarring
    3. Thin Cornea
    4. Herpetic Keratitis
  2. External eye conditions
    1. Blepharitis
    2. Dry Eye or sicca syndrome
    3. Allergic Conjunctivitis
  3. Other eye conditions
    1. Progressive Myopia
    2. Significant Cataract
    3. Uncontrolled Glaucoma
      1. Controlled Glaucoma is not an absolute contraindication
      2. Transiently increased extraocular pressure to 65 mmHg during procedure
      3. Intraocular Pressures may be falsely low and unreliable after LASIK
  4. Medical conditions
    1. Uncontrolled vascular disease
    2. Autoimmune Disease
    3. Immunocompromised status
    4. Pregnancy or Lactation
    5. Keloid formation history
    6. Uncontrolled Diabetes Mellitus (variable vision)
  • Technique
  • LASIK Technique
  1. Suction ring is applied to stabilize and flatten the Cornea
  2. Thin Corneal epithelial flap (160 u)
    1. Femtosecond Laser (cutting laser, all laser LASIK) creates thin Corneal flap OR
    2. Microkeratome creates thin Corneal flap (older technique)
  3. Computer programmed prior to surgery
    1. Corneal topography
    2. Refraction
  4. Pre-programmed excimer laser reshapes Cornea
    1. Laser emits UV light at Cornea (photoablation)
    2. Etches away Corneal Stroma under flap
      1. Myopia: Laser flattens central Cornea (shortens globe)
      2. Hyperopia: Laser flattens peripheral Cornea (lengthens globe)
      3. Astigmatism: Laser flattens steepest Meridian (smooths Corneal irregularities)
    3. Results in little to no adjacent thermal damage
  5. Recent advances in laser beam technology
    1. Smaller laser beam width <100 u
    2. Eye tracking systems adjust for eye movement
  6. Corneal flap repositioned without Suture
  7. Eye is irrigated
  8. Both eyes may be corrected on same day
  9. Vision recovered within 48 hours
  • Technique
  • Advancements
  1. Femtosecond Laser LASIK Technqiue (all laser LASIK)
    1. Laser replaces Microkeratome to create the Corneal flap (see above)
  2. Wavefront-guided LASIK
    1. Corneal re-shaping is adjusted per patient based on their underlying cylindrical aberrations
  1. Topical Corticosteroid eye drops
  2. Topical antibiotic eye drops
  3. Topical NSAID eye drops
  4. Eye shield use overnight following surgery
  5. No soft Contact Lens use for 1-2 weeks and no hard Contact Lens use for 3-4 weeks
  • Management
  • Follow-up
  1. Routine postoperative follow-up evaluations
    1. Day 1
    2. Week 1
    3. Month 1,3 and 6
  2. Warning signs necessitating follow-up
    1. Decreased Visual Acuity
    2. Suspected infection (redness)
    3. Pain
      1. Epithelial abrasion
      2. LASIK flap complication
  • Efficacy
  1. Uncorrected vision 20/20 achieved
    1. Low Myopia (<7 D): Up to 90%
    2. High Myopia (>7 D): 45%
  2. Uncorrected vision 20/40 achieved (adequate for driving)
    1. Low Myopia (<7 D): 90% (as high as 97-100%)
    2. High Myopia (>7 D): 85%
  • Advantages
  • Over other procedures (contrast with PRK)
  1. Minimal pain
  2. Quick visual recovery
  3. Treats high levels of Myopia
  4. Both eyes treated on same day
  5. LASIK enhancements easily performed within 12 months
  6. No stromal haze (unlike PRK)
  7. Satisfaction rate of 90% (PRK has 52% satisfaction)
  • Adverse Effects
  1. Minimal post-operative discomfort
  2. Glare or halos associated with outdoor lights (20%)
    1. Especially common with night driving
    2. Usually improves within months
  3. Dry Eyes or eye irritation (20-40%)
    1. First 3 months after surgery (resolves over 6-12 months, but may persist mildly in 20%, bothersome in 2%)
    2. Related to Corneal nerve innervation
    3. Treat with artificial tears (no preservative) prn, or Cyclosporine drops (Restasis)
  • Complications
  1. Repeat surgery to reshape Cornea: 5-30%
    1. Overcorrection or undercorrection
    2. Irregular Astigmatism
  2. Corneal Epithelium growth beneath flap: 1%
  3. Vision threatening infection: 1-5 per 10,000 procedures
  4. Loss of Visual Acuity that cannot be corrected: 0.1%
  5. Best spectacle-corrected vision worse than 20/40: <0.5%
  6. Corneal flap displacement: 0.5% (usually repairable)
  7. Buttonhole tear in Corneal flap precluding surgery
  8. Diffuse lamellar Keratitis (Sands of Sahara Syndrome)
    1. Sterile inflammatory response
    2. Occurs in 2-4% of patients
  • Precautions
  1. Does not correct accommodation loss with aging (presbyopia), esp. myopic patients
  2. Reading glasses will still be required
  3. Flap will not take up Fluorescein stain after LASIK