A 28-year-old with -6.00 D myopia, 530 µm central corneal thickness, and regular topography wishes to undergo refractive surgery. Corneal topography shows a normal Amsler-Krumeich pattern. The minimum residual stromal bed thickness after LASIK to avoid iatrogenic ectasia is:

• A 200 µm
• B 250 µm ✓
• C 300 µm
• D 350 µm

Explanation

The minimum safe residual stromal bed (RSB) thickness after LASIK is generally accepted as 250 µm to prevent post-LASIK ectasia. A thinner RSB leaves insufficient biomechanical support for the remaining cornea, risking progressive forward bowing (iatrogenic keratoconus). For a 530 µm cornea: flap (~110 µm LASIK flap) leaves 420 µm, then ablation depth for -6 D (~72 µm) leaves ~348 µm — which is above 250 µm, making LASIK feasible. Some centres use a stricter 300 µm cutoff. SMILE (flapless procedure) preserves more biomechanical integrity, allowing surgery in thinner corneas. The 200 µm threshold is considered unsafe by most international consensus panels.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.