Corneal collagen cross-linking
It was first developed in Germany in 1998 and clinical trials have been in course since the same year; in Italy clinical trials have been successfully performed since 2005, while in the USA clinical trials commenced only in 2008. The procedure, with epithelium removed, is approved for use throughout Europe.
The cross-linking involves a one-time application of riboflavin solution to the eye that is activated by illumination with UV-A light for approximately 30 minutes. The riboflavin causes new bonds to form across adjacent collagen strands in the stromal layer of the cornea, which recovers and preserves some of the cornea's mechanical strength. The corneal epithelial layer is generally removed to increase penetration of the riboflavin into the stroma.
In some cases, collagen cross-linking may also be combined with other treatments to improve corneal strength or optical refraction. Successful treatment methods include Mini Asymmetric Radial Keratotomy (M.A.R.K.), corneal ring segment inserts (Intacs or Ferrara rings), topography-guided laser, or Keraflex. Corrective lenses are normally required after these treatments, but with smaller, more normalized prescriptions. Increased corneal symmetry allows for more comfortable contact lens wear, often of daily disposable lenses. These newer methods have an important role in limiting deterioration of vision, increasing unaided and uncorrected vision, and strongly reducing the case for corneal transplantation.
Patients that are considered for treatment must undergo an extensive clinical workup, including computerized corneal topography, endothelial microscopy, ultrasound pachymetry, b-scan sonography, keratometry and biomicroscopy.
|This section requires expansion. (July 2013)|
The standard cross-linking technique, also called Dresden protocol (CXL) requires the removal of central 9 nm of corneal epithelium layer (epi-off), followed by 30 minutes of riboflavin administration, subsequently, UVA light is applied for 30 minutes.
In transepithelial or epithelium-on (epi-on) cross-linking technique, the corneal epithelium layer is left intact. Brian Boxer Wachler was the first to perform transepithelial crosslinking in 2004. in this technique, because the epithelium is not removed, riboflavin loading requires more time than with epi-off techniques.
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