Other Vision Surgery
Corneal cross linking types, Symptoms and Treatment
Reviewed by William Trattler, MD
Corneal cross-linking is a minimally invasive outpatient procedure designed to treat progressive keratoconus (and, sometimes, other conditions that cause a similar weakening of the cornea).
The corneal cross-linking procedure strengthens and stabilizes the cornea by creating new links between collagen fibers within the cornea. The two-step procedure applies liquid riboflavin (vitamin B2) to the surface of the eye immediately followed by a controlled exposure of the eye to ultraviolet light.
The two basic types of corneal cross-linking are:
- Epithelium-off cross-linking. In this procedure, the thin outer layer (epithelium) of the cornea is removed to allow the liquid riboflavin to more easily penetrate the deeper corneal tissue.
- Epithelium-on cross-linking. In this procedure (also called transepithelial cross-linking), the protective corneal epithelium is left intact, making it a less invasive procedure than cross-linking with epithelium removal.
Corneal cross-linking can be combined with other procedures for keratoconus treatment. For example, it can be performed along with implantation of tiny arc-shaped corneal inserts called Intacs to reshape and stabilize the cornea in more advanced cases of keratoconus.
Currently, the only corneal cross-linking platform that is FDA-approved for the treatment of progressive keratoconus in the U.S. is Avedro's KXL System, which includes the company's proprietary Photrexa and Photrexa Viscous riboflavin solutions.
The FDA approves medications and treatments for a specific use. Avedro's KXL System has FDA approval for epithelium-off cross-linking only. However, a doctor in the United States can legally use FDA-approved medications and treatments in another reasonable way that he or she considers appropriate. This is called an "off-label" use, and it's a common way to expand the use of an FDA-approved medication or procedure without having to undergo the often long and very expensive FDA approval process.
Corneal cross-linking (CXL) strengthens a weak or thin cornea with a combination of riboflavin solution and controlled UV light. (Image: Avedro, Inc.)
So, though Avedro's KXL System is FDA-approved only for epithelium-off cross-linking, eye surgeons can lawfully use riboflavin solutions, other proprietary formulations and UV light to perform less invasive, epithelium-on cross-linking for keratoconus.
Holcomb C3-R Corneal Cross-linking
One of the pioneers in the development of corneal cross-linking treatment for keratoconus is Brian Boxer Wachler, MD, an eye surgeon who founded the Boxer Wachler Vision Institute in Beverly Hills, California. Dr. Boxer Wachler also is an AllAboutVision.com Editorial Advisory Board member.
In 2007, Boxer Wachler was visited by U.S. Olympic bobsledding champion Steve Holcomb. Holcomb was suffering from progressive keratoconus that was degrading his vision to the point of legal blindness and was about to end his bobsledding career.
Boxer Wachler performed an epithelium-on cross-linking procedure to reshape and stabilize Holcomb's misshapen cornea, combined with implantation of a phakic IOL to further improve the athlete's vision.
The procedures were a huge success, and in February 2010 at the Winter Olympics in Vancouver, Holcomb and his teammates won an Olympic gold medal — the first in bobsledding for the United States in 62 years.
To honor the athlete, Boxer Wachler named his transepithelial cross-linking procedure the Holcomb C3-R and continues to perform the off-label procedure with excellent results. (Watch Dr. Boxer Wachler's appearance on The Doctors, where he describes the Holcomb C3-R cross-linking procedure.)
Best Candidates for Corneal Cross-linking
Corneal cross-linking is most effective if it can be performed before the cornea has become too irregular in shape or there is significant vision loss from keratoconus. If applied early, cross-linking typically will stabilize or even improve the shape of the cornea, resulting in better visual acuity and an improved ability to wear contact lenses.
Other potential applications of cross-linking include the treatment of corneal ulcers
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