Your Ophthalmology Study Assistant
Razeen answers study questions on refractive surgery, keratoconus and corneal ectasia, corneal imaging, astigmatism, cataract surgery, IOL calculation, clinical optics and refraction, in clear and concise language.
AI-generated. Educational use only, not medical advice.
The question
What residual stromal bed thickness is considered safe after LASIK?
Razeen answered
The commonly accepted minimum residual stromal bed (RSB) thickness for LASIK is 250 µm, though some authors recommend 250-300 µm.
However, this number should be treated as a guideline rather than a true safety cutoff:
- Ectasia has occurred after LASIK even with RSB greater than 300 µm, and many eyes tolerated LASIK without ectasia at RSB below 225 µm. Risk therefore appears to be a continuum without a definitive cutoff.
- Because calculated RSB can be inaccurate, intraoperative pachymetry is recommended for patients at risk of low RSB.
Percent tissue altered (PTA) is more discriminative than RSB alone; a PTA of 40% or more is significantly associated with ectasia even in eyes with normal preoperative topography.
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