Corneal cross-linking, commonly abbreviated as CXL, is a new treatment designed to strengthen the cornea, the clear tendon in the front of the eye. This treatment was recently approved by the FDA in the United States, but has been done with great success around the world for more than ten years. There are hundreds of peer reviewed scientific articles in the ophthalmic literature demonstrating the efficacy of this procedure. Dr. Petashnick at Manchester Ophthalmology was one of the Avedro study sites in the US, which provided data for the FDA approval.
What is CXL?
As noted above, corneal cross-linking, or CXL, is a procedure that strengthens the cornea. A vitamin B2 complex, riboflavin, is saturated into the cornea, and then is exposed to ultraviolet light. The riboflavin and the ultraviolet light create a chemical reaction which strengthens the corneal tissue (collagen) causing the the cornea to become more rigid. The CXL treatment is used in conditions where the cornea is weak.
The procedure that has been FDA-approved in the US requires epithelium-off cross-linking. During epithelium-off CXL, your doctor removes the cover cells of the cornea (the epithelium) in order to introduce the riboflavin to the deeper layers of the cornea (the stroma). The Riboflavin molecule in it’s current formulation is quite large, and cannot pass into the deeper corneal layers through the epithelium, and this is why the cover cells are removed. Removal of the epithelium takes about one minute and is done under topical anesthetic. Most people do not have any pain with removal of the epithelium, but feel mild pressure.
After removal of the epithelium, riboflavin is applied to the cornea every two minutes for a total of thirty minutes. After the thirty minutes, treatment with the ultraviolet light is started. Ultraviolet light is applied to the eye for a total of 30 minutes. Throughout the exposure to the ultraviolet light, riboflavin is still applied every two minutes. The total time for CXL is a little more than an hour.
When the treatment is completed, a bandage contact lens will be applied to the eye. As the cover cells of the cornea have been removed, one is left with an abrasion. The contact lens allows for the eye to be more comfortable after the treatment until the cover cells heal. The epithelium usually heals within three to five days. The contact lens is removed once the cover cells have healed. There can be pain due to the cornea abrasion, therefore pain medication is provided. Antibiotic drops and anti-inflammatory drops will need to be applied for about two to four weeks after the treatment.
This treatment protocol is the only protocol approved by the FDA in the U.S. and is used for all the indications for cross-linking.
Conditions treated with CXL:
Keratoconus is a progressive eye disease that causes the normally spherical shaped cornea to bulge into a more cone like shape. The conical shape of the cornea causes light to be scattered and distorted instead of being focused clearly to the back of the eye. Many people describe blurred vision and rays of light that appear in many directions. Despite an attempt to correct the vision with glasses or contact lenses, the vision remains distorted. Collagen-crosslinking has been shown to stop the progression of keratoconus in almost all patients, and also to flatten the conical shape of the cornea thereby improving the quality of vision.
The ideal candidates for cross-linking are those young patients first diagnosed with keratoconus because the treatment can stop progression of the disease before the cornea becomes significantly distorted. Patients have been treated as young as eight years of age. The goal of treatment is to prevent the need for a corneal transplant.
As patients approach their forties, however, the rate of progression of keratoconus slows. Collagen cross-linking in patients over age 40 is performed primarily to flatten the cornea and create a more regular optical surface to improve vision, and is performed less to slow the progression of the disease.
The improvement of the cornea’s shape after cross-linking is seen most prominently from six to twelve months after treatment, and continued improvement of the corneal shape may continue for a number of years.
Cross-linking is not indicated for every patient with keratoconus. Patients with keratoconus presenting with very steep corneas and severe corneal thinning will require alternative treatments such as a corneal transplant.
2. Post-LASIK Ectasia
Patients who have had LASIK or PRK and develop a progressively irregular cornea will also benefit from cross-linking to stabilize the cornea. This condition is referred to as post-LASIK ectasia. The procedure works the same way as in keratoconus; cross-linking will strengthen the cornea and prevent progression of the corneal irregularity.
3. Post-RK fluctuation in vision
Patients who have had RK and have fluctuation of their vision throughout the day due to corneal instability, are also candidates for cross-linking. The cross-linking will strengthen the cornea and prevent the change in corneal curvature that occurs at different times of the day.
Manchester Ophthalmology is not currently offering the collagen cross-linking procedure due to insurance difficulties.