Corneal collagen cross-linking
Corneal collagen cross-linking with riboflavin (vitamin B2) and UV-A light (also known as CXL, C3-R, CCL and KXL), better known as Cross-linking, is a parasurgical treatment for corneal ectasia such as keratoconus.
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 or less 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.
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.
In transepithelial or epithelium-on (epi-on) cross-linking technique which was first performed in 2004 in the U.S., the corneal epithelium layer is left intact. in this technique, because the epithelium is not removed, riboflavin loading requires more time than with epi-off techniques.
Contact lens-assisted cross-linking (CACXL) may be performed for patients with corneal stromal thickness between 350 µm to 400 µm after epithelial removal. in this method a pre-corneal riboflavin film, a riboflavin-soaked UV barrier-free soft contact lens of negligible power and a pre-contact lens riboflavin film are used to decrease UV irradiance to safe levels at the level of the endothelium.
Combination with refractive eye surgeries
Cross-linking is not intended to correct vision, thus it is usually combined with refractive eye surgeries such as photorefractive keratectomy and intrastromal corneal ring segments. Cross-linking can also be used to avoid post-LASIK ectasia and to improve refractive outcomes.
It was first developed in Germany in 1998 and clinical trials have been in course since the same year; in Italy routine interventions 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 and Canada.
In February 2015, amid concerns about study data and labeling, a FDA panel recommended approval of Avedro’s combined riboflavin ophthalmic solutions and ultraviolet light irradiation for corneal collagen cross-linking. In March 2015, FDA decided not to approve the Avedro's new drug application, identifying areas of the application concerning the device which require additional information.
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- Kathryn M. Hatch, William B. Trattler. (16 May 2012). "Corneal Crosslinking: Epi-on or Epi-off?". Medscape.
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- Agarwal, Amar; Jacob, Soosan (August 10, 2014). "Contact lens-assisted cross-linking treats corneal ectatic disorders in thin corneas". Ocular Surgery News U.S. Edition.
- Jacob, Soosan. "Contact Lens-Assisted CXL for Thin Corneas". Cataract & Refractive Surgery Today.
- Stephenson, Michelle. "LASIK Xtra: Is It for Everyone?". Review of Ophthalmology.
- "FDA panel recommends approval of riboflavin, UV for keratoconus, corneal ectasia". Healio. Ocular Surgery News. 24 February 2015.
- Lowes, Robert (27 February 2015). "Corneal Crosslinking Drug Gets Cautious Nod From FDA Panel". Medscape.
- "FDA Does Not Approve Avedro's Corneal Cross-Linking Platform Application, Requesting Additional Information". Eyewire Today. 31 March 2015.
|Wikimedia Commons has media related to corneal collagen crosslinking.|
- Corneal Collagen Cross-Linking on National Keratoconus Foundation website.
- Corneal Collagen Cross-Linking on EyeWiki from the American Academy of Ophthalmology