CXL is usually not recommended when patients have:
- A corneal thickness of less than <400 µm (due to the risk of endothelial damage). However, a hypotonic riboflavin solution may be used to increase the pre-operative stromal thickness of thin keratoconus corneas to 400µm and allow CXL to be performed.
- A history of incisional refractive surgery such as radial keratotomy or astigmatic keratotomy (because it may cause keratotomy incisions to rupture).
- Central corneal opacities and associated poor best-corrected visual acuity.
- Severe dry eye (because it may hinder reepithelialisation and thereby increase the risk of post-surgery infection).
- Herpes simplex keratitis (as corneal melting can occur).
- Severe keratoconus (with a preoperative keratometry reading of >58 D – as this presents a greater risk of continued keratoconus progressionand permanent post-operative stromal haze).
- Systemic collagen diseases and/or are pregnant or nursing mothers (because insufficient investigations into the safety of the treatment in these populations has been carried out).
- A preoperative CDVA of better than 20/25 and are over the age of 35 years old (due to there being a higher risk of complications than with younger patients).