Laser In-Situ Keratomileusis

1. 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)
2. Criteria: LASIK (and PRK)
   1. Age 18 years or older
   2. Stable Refraction for at least 1 year
   3. Myopia -0.50 to -12.00 diopters
   4. Hyperopia less than +0.50 to +4.00 diopters
   5. Astigmatism less than or equal to 8.0 diopters
   6. Adequate Corneal thickness
   7. No contraindications below
3. Contraindications
   1. Ocular
      1. Keratoconus
      2. Herpetic Keratitis
      3. Progressive Myopia
      4. Corneal disease
      5. Cataract
      6. Corneal Scarring
      7. Dry eye
      8. Blepharitis
      9. Thin Cornea
      10. Glaucoma
          1. Not an absolute contraindication
          2. Relative contraindication due to transiently increased extraocular pressure to 65 mmHg during procedure
   2. Medical
      1. Uncontrolled vascular disease
      2. Autoimmune disease
      3. Immunocompromised status
      4. Pregnancy or Lactation
      5. Keloid formation history
      6. Diabetes Mellitus
4. Technique: MicroKeratome LASIK Technique
   1. Microkeratome creates thin flap (160 u) in Cornea
   2. Computer programmed prior to surgery
      1. Corneal topography
      2. Refraction
   3. 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
         2. Hyperopia: Laser flattens peripheral Cornea
         3. Astigmatism: Laser flattens steepest Meridian
      3. Results in little to no adjacent thermal damage
   4. Recent advances in laser beam technology
      1. Smaller laser beam width <100 u
      2. Eye tracking systems adjust for eye movement
   5. Corneal flap repositioned without Suture
   6. Both eyes may be corrected on same day
   7. Vision recovered within 48 hours
5. Technique: Advancements
   1. Femtosecond Laser LASIK Technqiue (all laser LASIK)
      1. Suction ring is applied to stabilize and flatten the Cornea
      2. Laser replaces Microkeratome to create the Corneal flap
      3. Flap is lifted and computer directs laser to remove a predefined amount of Corneal tissue
      4. Flap is returned and eye is irrigated
   2. Wavefront-guided LASIK
      1. Corneal re-shaping is adjusted per patient based on their underlying cylindrical aberrations
6. Management: Discharge medications
   1. Topical Corticosteroid eye drops
   2. Topical antibiotic eye drops
   3. Topical NSAID eye drops
   4. Eye shield use overnight following surgery
7. 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
8. Efficacy
   1. Uncorrected vision 20/20 achieved
      1. Low Myopia (<7 D): 60% (as high as 67-83%)
      2. High Myopia (>7 D): 45%
   2. Uncorrected vision 20/40 achieved (ok for driving)
      1. Low Myopia (<7 D): 90% (as high as 97-100%)
      2. High Myopia (>7 D): 85%
9. 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)
10. Adverse Effects
    1. Minimal post-operative discomfort
    2. Glare or halos associated with outdoor lights
       1. Usually resolves within months
    3. Dry Eyes (20-40%)
       1. Typical for first 3 months after surgery
       2. Related to Corneal nerve innervation
       3. Treat with artificial tears (no preservative) prn, or cyclosporine drops (Restasis)
11. 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. Best spectacle-corrected vision worse than 20/40: <0.5%
    5. Corneal flap displacement: 0.5% (usually repairable)
    6. Buttonhole tear in Corneal flap precluding surgery
    7. Diffuse lamellar Keratitis (Sands of Sahara Syndrome)
       1. Sterile inflammatory response
       2. Occurs in 2-4% of patients
12. Precautions
    1. Does not correct accommodation loss with aging
    2. Reading glasses will still be required
    3. Flap will not take up Fluorescein stain after LASIK
13. References
    1. (1999) Med Lett Drugs Ther 41(1068):121-3
    2. Bower (2001) Am Fam Physician 64(7):1183-90
    3. Messmer (2010) Am Fam Physician 81(1): 42-8
    4. Perez-Santonja (1999) Ophthalmology 106:21
    5. Waring (1999) Invest Ophthalmol Vis Sci 40:S588
    6. Stulting (1999) Ophthalmology 106:13