Patient Selection for Refractive Surgery

General Candidacy - The Starting Line

• Age: ≥18 years (ideally ≥21 years for refractive maturity).
• Refractive Stability: Paramount.
  • Change in Spherical Equivalent (SE) <0.50 D over 12 months.
  • Verified by ≥2 refractions (cycloplegic if possible).
• Motivation & Expectations:
  • Strong desire for spectacle/contact lens independence.
  • Realistic understanding of risks, benefits, limitations, alternatives.
• Systemic Health:
  • Good general health.
  • No uncontrolled:
    • Autoimmune diseases (e.g., SLE, RA).
    • Immunodeficiency.
    • Diabetes Mellitus (poorly controlled can affect healing & refraction).
• Ocular Health:
  • No active ocular disease:
    • Severe Dry Eye Syndrome (DES).
    • Keratitis, Uveitis.
    • Uncontrolled Glaucoma.
    • Progressive corneal ectasias (Keratoconus, PMD).
• Key Contraindications (Absolute):
  • Pregnancy or breastfeeding.
  • Unrealistic expectations.
  • Sole functioning eye (relative to absolute, requires extreme caution).

⭐ Documented refractive stability (<0.50D change in SE over 1 year) is the cornerstone of patient selection.

Ocular Examination - Eye Spy Fitness

Key assessments to ensure suitability for refractive surgery:

• Visual Acuity & Refraction:
  • Uncorrected (UCVA) & Best-Corrected Visual Acuity (BCVA).
  • Manifest & Cycloplegic refraction: Stability essential (change < 0.5D in 1 year).
• Corneal Evaluation:
  • Topography/Tomography:
    • Assesses corneal shape, power (K-values: avg 40-47D), regularity.
    • Screens for ectasia (e.g., Keratoconus, Pellucid Marginal Degeneration).
    • 
  • Pachymetry:
    • Measures Central Corneal Thickness (CCT).
    • Min CCT for LASIK often > 500 µm.
    • Crucial for calculating Residual Stromal Bed (RSB) thickness (target > 250-300 µm).
• Pupil Size:
  • Scotopic pupil diameter measurement.
  • Large pupils (> 6-7 mm) may ↑ risk of night vision issues (halos, glare) if > optical zone.
• Tear Film Assessment:
  • TBUT, Schirmer's test.
  • Identify & treat pre-existing Dry Eye Disease (DED).
• Intraocular Pressure (IOP):
  • Rule out glaucoma or ocular hypertension. Normal range 10-21 mmHg.
• Slit-Lamp Examination:
  • Detailed anterior segment evaluation (lids, conjunctiva, cornea, lens).
  • Rule out blepharitis, active infection, cataract.
• Fundoscopy (Dilated):
  • Posterior segment health (retina, optic nerve). Rule out retinal pathology.

⭐ Belin/Ambrósio Enhanced Ectasia Display (BAD) on Pentacam is a crucial tool to unmask subtle corneal ectatic changes, aiding in identifying unsuitable LASIK candidates.

Contraindications - Red Flags & Alerts

• Absolute Contraindications:
  • Age < 18 years (typically < 21 yrs for stability)
  • Unstable refraction: > 0.5D change/year
  • Corneal ectasias: Keratoconus, PMD
  • Insufficient corneal thickness (pachymetry < 480-500 µm)
  • Active ocular infection (e.g., active herpes, microbial keratitis) or active uveitis
  • Uncontrolled systemic diseases: active autoimmune dz, immunodeficiency
  • Pregnancy or breastfeeding
  • Unrealistic patient expectations
  • Monocular patient (strong relative/absolute)
• Relative Contraindications (Caution Advised):
  • Severe Dry Eye Disease (optimize pre-operatively)
  • Glaucoma (IOP monitoring challenges, steroid response)
  • History of HSV keratitis (reactivation risk; consider prophylaxis)
  • Large pupils (>7mm scotopic) (night vision issues: glare, halos)
  • Diabetes Mellitus (well-controlled; monitor healing, refractive stability)
  • History of keloid formation
  • Certain systemic medications (e.g., amiodarone, isotretinoin, sumatriptan)

⭐ Forme fruste keratoconus (FFKC), often subtle and missed on basic exam, is an absolute contraindication due to high risk of iatrogenic ectasia post-LASIK.

High-Yield Points - ⚡ Biggest Takeaways

• Stable refraction for at least 1 year is a primary criterion.
• Minimum age is typically 18-21 years; ensure skeletal maturity.
• Crucial: Adequate corneal thickness (pachymetry >500µm), ensuring sufficient residual stromal bed (RSB >250-300µm).
• Absolute contraindications: Keratoconus, active ocular surface disease, uncontrolled systemic conditions (e.g., autoimmune).
• Realistic expectations and patient motivation are key for success.
• Evaluate mesopic pupil size to minimize postoperative night vision symptoms.
• Pregnancy and lactation are temporary contraindications.