Corneal Cross Linking (also known as CXL, 3CR or C3-R) is a process which attempts to strengthen the cornea.
In conditions such as keratoconus, the cornea is fragile and over time becomes increasingly distorted as they eye is too fragile to retain its regular shape. CXL came about in an attempt to strengthen these weak corneas to prevent progression of the condition.
It was pioneered in the early 1990s by Prof Thoe Seiler and Prof Eberhard Spoerl in Dresden and has been gaining interest and acceptance quickly since then even to the point of approval by the NHS
The cornea (the clear window at the front of the eye) is made up of many loose layers of collagen stacked on top of each other. These layers are held to one another by bonds which â€˜cross linkâ€™ between the layers and stiffen the cornea prevent the layers moving over one another as easily.
Some crosslinking occurs naturally over time, and therefore with age the cornea does stiffen. This perhaps helps us explain why typically keratoconus progresses most during the teens and 20s and then starts to slow down during the late 20s and 30s. Most patients with keratoconus stabilise in middle age and this natural crosslinking is thought to be the cause.
The CXL procedure aims to increase crosslinking medically to strengthen the cornea sooner and prevent the condition progressing. The front layer of cells of the cornea (epithelium) are removed from a 7-9mm central section of the cornea. After instilling repeated doses of a special light sensitive preparation of riboflavin (vitamin B12) and dextran for about 30minutes, the cornea is exposed to UVA light for another 30minutes. The riboflavin and the the UVA light react to release oxygen radicals creating the new cross links.
After the procedure the epithelium must regrow so antibiotic drops are required to prevent infection. The eye is quite uncomfortable for a few days while this takes place and other drops or special contact lenses may be used to promote healing.
The process of cross linking continues for several days after treatment but the effect on the overall corneal shape and strength may take much longer.
(Although this is the accepted explanation of crosslinking the precise mechanics at a molecular level are poorly understood and the effect may even not be due to these crosslinks at all.)
Yes but make sure you read about the limitations of the procedure. A number of long term studies have demonstrated the effectiveness of CXL in stabilising keratoconus and its safety as a procedure. The original researchers from Dresden published 6 years results in 2008 which showed stabilisation of the cornea in most cases.
A good sign that the treatment is effective is that is has recently been approved for used in the NHS. The NHS regulators spend a long time examining the effectiveness, safety and costs vs benefits of new treatments and when something is approved it is an indicator it is an effective treatment.
Given that progression of keratoconus occurs naturally with age, it is most suitable for younger patients and ideally before the keratoconus has progressed too far. However, any person with keratconus or a related condition who has documented progression of their condition in the last year is suitable for the procedure.
CXL does not cure keratoconus. It is designed only to prevent further progression of the condition so at best the shape of cornea remains the same. It is not a way of reducing your dependance on contact lenses or glasses.
You must have a minimum corneal thickness of 0.4mm in order to protect the other corneal layers from UVA exposure. This means some people with advanced keratoconus will not be suitable as the cornea progressively thins over time in the condition.
If your keratoconus is stable (not progressing) then CXL is not recommended and probably not even necessary. However given the relative ease of performing the procedure and the lack of complications, there is an argument to treat all people with keratoconus when the condition is first diagnosed to prevent any progression â€˜just in caseâ€™.
CXL is performed at eye hospitals and private clinics around the country and is available in Edinburgh. You will need to be seen at the eye hospital to be eligible so come and see us at Cameron Optometry and we can discuss your options further and initiate the referral procedure if appropriate.
Given its huge potential, much research is now underway in CXL and improvements to the procedure. The following are a list of avenues of research currently going in in different places around the world:
Epithelium on â€“ the procedure is quite uncomfortable because of the removal of the epithelium and so much effort is being put into performing the procedure without removing this layer of cells. The difficulty is that the riboflavin drops do not penetrate the cornea well through the epithelium. Special formulations are being developed to aid absoprtion.
Treatment times â€“ using different riboflavin formlations and higher powered UV light, the duration of the whole procedure is gradually being reduced which is better for the patient and hopefully safer too.
Flashlinking â€“ this uses a different agent from riboflavin and has the advantage of only need 30 seconds of UV exposure rather than 30minutes. This procedure needs further investigation before it can be introduced into clinical practice.
Combination treatments â€“ some practitioners are using CXL to strengthen corneas before performing laser surgery that previously would have been impossible to do on such thin and fragile corneas without CXL. Other combinations include performing CXL in conjunction with INTACS which are ring shaped implants embedded in the cornea that help normalise the shape of the cornea.
These combination treatment are still very experimental as they are so new and further research is required before it can be recommended as a routine treatment.
Alternative uses â€“ when it was first described CXL generated a lot of excitement about its use in strengthening the cornea in all sorts of ways, for example after damage to the cornea has created a wound, or after Laser surgery. The results of CXL in these cases has been much less impressive than we hoped which leads us question whether we really know how crosslinking works at a molecular level. Some recent papers have shown that CXL can be effective in treating serious corneal infections as the UV light used, sterilises the cornea killing the infecting organism before the riboflavin strengthens the healing tissues.
If you have any questions about CXL or keratoconus and related conditions or simply want our expert assessment of the health of your eyes and advice on treatment options, come and see us.