A 20-year-old patient with keratoconus has a contact lens intolerance and best corrected VA of 6/36 with irregular astigmatism. Corneal topography shows inferior steepening with a SimK of 55 D. He is offered corneal collagen cross-linking (CXL). Which of the following is the minimum corneal thickness required for standard (Dresden protocol) CXL?
- A 400 µm after epithelial removal ✓
- B 300 µm
- C 500 µm
- D 250 µm
Correct answer: A. 400 µm after epithelial removal
Explanation
The standard Dresden CXL protocol (epithelium-off technique) uses riboflavin 0.1% drops with UVA irradiation (3 mW/cm² for 30 minutes). The minimum corneal stromal thickness required is 400 µm after epithelial debridement; this ensures the UVA irradiance does not penetrate to the endothelium (5.34 mm UVA depth of penetration standard). Thinner corneas risk endothelial cell damage from UVA. For thinner corneas, a hypotonic riboflavin solution may be used to swell the stroma, or transepithelial (epithelium-on) accelerated protocols are considered.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.