A myopic patient has an eyeglass prescription of -6.0 DS. She wants LASIK. Her corneal topography shows a K-max of 47.0 D, central corneal thickness 520 μm, and normal topographic pattern. The minimum residual stromal bed thickness after ablation must be maintained at:

• A 250 μm residual stromal bed to prevent post-LASIK ectasia ✓
• B 200 μm residual stromal bed to prevent post-LASIK ectasia
• C 300 μm residual stromal bed to prevent post-LASIK ectasia
• D 350 μm residual stromal bed for a high myope of this degree

Explanation

The critical threshold for residual stromal bed (RSB) after LASIK flap creation and excimer ablation is 250 μm — below this threshold, the structural integrity of the cornea is compromised, risking post-LASIK ectasia (iatrogenic keratectasia). For -6.0 D myopia, each diopter requires approximately 15 μm of ablation depth (Munnerlyn approximation), so ~90 μm ablation plus a standard 120 μm flap = 210 μm removed from 520 μm = 310 μm RSB — this is adequate. However, if RSB would fall below 250 μm, LASIK should not be performed; PRK/LASEK (no flap) or ICL would be considered.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.