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Collagen

Reproduced by courtesy of KC Group.
www.keratoconus-group.org.uk

Many of you will have heard about a promising new treatment for keratoconus called collagen crosslinking (CXL). We are very grateful to Mr Chad Rostron, consultant ophthalmologist at St George's and Moorfields Hospitals for giving a talk on CXL at our AGM in March. This is a summary of his presentation.

Collagen crosslinking involves removal of the surface corneal epithelial cell layer, saturation of the cornea with 0.1 % riboflavin for 30 minutes (1 drop is applied every 2 minutes) followed by application of UV light for 30 minutes. The corneal thickness needs to be over 400 microns for the procedure to be safe and effective. The
technique was developed by Theo Seiler in Dresden. Treatments started in 1998, although initially only a handful were carried out each year, and it was not until 2005 that the Dresden clinic was treating over 100 patients per year with CXL. There is still some controversy about the treatment because none of the studies reported are randomised control trials. Mr Rostron showed the most recent results (December 2007) from the Dresden clinic, following up 302 patients (501 eyes) for between 1 and 7 years. The procedure was carried out on patients with proven progressive KC and between half and two thirds showed a gradual and progressive improvement in vision over 3 years, a decrease in astigmatism and a reduced steepness of the cornea. Of the patients who did not show an improvement, the majority had unchanged vision, astigmatism and steepness, with only a few showing deterioration. In a group of patients with progressive KC, one would normally expect greater numbers with deteriorating acuity so it appears that CXL prevents further sagging and distortion. In order to achieve good penetration of the riboflavin, the corneal epithelium (the outer layer) needs to be stripped off. The riboflavin is mixed in a dextran solution to prevent swelling of the cornea during treatment. The riboflavin then absorbs almost all of the UV light, with only 2% getting through to the back of the eye. It is important that the UV light does not damage the back surface of the cornea (the endothelium) hence the requirement of a minimum thickness of 400 microns for the cornea. The result of CXL is to stiffen the cornea, producing an increase in the diameter of individual collagen fibres and effectively freezing the corneal shape and preventing further degeneration. It is effectively accelerating the ageing process of the cornea: older people have naturally thicker corneas. Trials at Moorfields

The first pilot study, where half the patients were given CXL and half CXL with orthokeratology (wearing a bandage lens for 7 days prior to treatment to reshape the cornea) is now complete, but no results are yet available. Current trails are focusing on opening up the possibility of linking CXL to other treatments: a) lntacs (Intacs alone do not stabilise KC, so it makes sense to combine the two),
b) topography guided surface laser treatment to make the cornea shape more
regular (while LASIK generally makes KC worse, doing it after CXL would increase the safety margin), c) phakic intro-ocular lens implantation (not usually used in progressive KC because of likely changes in refraction - but combining it with CXL may make sense), d) CXL on corneas less than 400 microns thick by temporarily swelling the cornea.

During the question and answer session which followed, Mr Rostron explained that Moorfields have set 40 years as the upper age limit for the trials (after 40 most corneas thicken naturally). He felt that treatment should be targeting younger patients as these are the ones likely to get most benefit, but it is difficult to get ethical approval for trials in under 18s. After CXL, the eye will be sore for 3 or 4 days, a bandage lens is worn and painkillers given. Patients cannot wear a contact lens for several months after the treatment. Scarring on the cornea caused by ulcers or infection is a contraindication for CXL because the treatment would spread the 'dodgy' cells around. CXL does carry the risk of potentially serious side effects (infective keratitis, a risk of scarring on the surface of the cornea and a risk of haze). CXL is equivalent to lifetime progressive thickening of the cornea, so in theory this is a treatment that should only need to be done once. Evidence form the trails should be available within a year or two, which could open the way for CXL to be available on the NHS. The Moorfields trials are open to non-Moorfields patients on referral. Other hospitals are also carrying out trials.

 

Paul Tomlins, Specialty Registrar at the Birmingham and Midland Eye Centre writes: Collagen Crosslinking is an exciting new development in the treatment of keratoconus. Collagen Crosslinking is a non-invasive treatment which has shown promise in small scale early trials. We are intending to run a large randomised controlled trial in Birmingham, in collaboration with St Thomas' Hospital in London into the effectiveness of Collagen Crosslinking. For further information, please contact Paultomlins@mac.com. An ophthalmologist at Windor is also involved in trials. The KC Group would be interested to hear if members are aware of any other NHS CXL trials elsewhere in the UK.