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Corneal cross-linking (CXL)

Corneal crosslinking is a method of dealing with a condition called keratoconus.

The crosslinking is not that the eyeballs become linked, rather that the collagen inside each eyeball is linked with that close to it. Keratoconus is a condition in which the eyeball itself becomes misshaped. Our eyes work by focussing light onto the retina, this is done by the shape of the eyeball itself as well as the lens. With age the corona, the front part of the eye, can become thinner and weaker.

This weakness can lead to the eyeball changing shape and thus vision deteriorating. Things become blurry and it becomes hard to see. Keratoconus is something that comes with age, but it is not necessarily something associated with old age. Often the presentation is in late childhood to early adulthood. The name itself comes from the typical “cone” shape that the eye takes on rather than the more usual ball. Corneal crosslinking is a method of strengthening the cornea to arrest this change.

The technique is to add a certain eye drop to the eyes then ultraviolet light. This causes the collagen strands in the eye to link to each other, this net then strengthening the front of the eye as a whole. This stops, or sometimes just reduces, the ongoing change in eyeball shape and vision deterioration.

There are two types of corneal crosslinking, “epi-on” and epi-off.

This refers to the epithelium, the very surface of the cornea at the front of the eye. In the epithelium off method this is first raised off the eye to allow access to the eye drops and then the light. The epi-on method is still experimental and is often not covered by insurance policies as yet.

Keratoconus is a progressive condition. This means that without treatment it will continue to get worse.

Keratoconus will rarely lead to total blindness but the change of the eyeball shape from round to a cone shape will make vision progressively worse. If this continues to happen then the only treatment is a corneal transplant which is significant surgery.

Corneal crosslinking usually arrests the progression of the keratoconus and both stabilises vision and avoids that later surgery. Corneal crosslinking is therefore the recommended treatment for keratoconus. It is also recommended that if you do have keratoconus then you do have corneal crosslinking as without treatment it is likely to continue to get worse.

Corneal crosslinking is not a cure for keratoconus, it is a stabilisation of it. The procedure does not reverse changes in eyeball shape and thus focus and vision that have already taken place.

Corneal crosslinking instead tries to ensure that the changes do not get worse, that there is no progressive deterioration in sight. It is therefore better to have corneal crosslinking early, when the keratoconus problem is first identified.

An early sign that corneal crosslinking might be recommended is seeing “ghost” images. Multiple and randomly distributed around the eye images of the same thing.

Within the cornea there are strands, fibres, of collagen. The aim of corneal crosslinking is to make these connect with each other and thereby create crosslinks which strengthen that part of the eye.

This provides greater resistance to the progressive changes in eyeball shape. The crosslinking is done by adding riboflavin (Vitamin B2) to the eye. This allows the cornea to absorb more light. Then ultraviolet light is shone into the eye, onto the cornea.

The light itself is produced by a laser which provides exactly the correct wavelength necessary to promote the reaction in the collagen. The procedure takes place in the surgery or office. Anaesthetic drops are added to your eye to numb it. If necessary, something can be provided to calm you.

Then the riboflavin is added and this takes about 30 minutes to properly soak in. You will be asked to lean back, and the UV light will be shone into your eyes. The whole procedure will take one hour to perhaps 90 minutes to complete.

The difference between epi-on and epi-off is that in the experimental, epithelium on, method that part of the eye is left in place while the treatment is performed. In the epi-off method the consultant will lift the epithelium off the cornea before adding the eye drops and then proceeding with the treatment.

You should not wear perfume, aftershave or make up on the day of the operation. As the anaesthetic used is a local one, drinking liquids and a light meal beforehand are usually allowed.

The procedure itself might take 60 to 90 minutes. You may not drive immediately afterwards, you should have someone to take you home with you. Discomfort is likely for several days afterwards. Significant pain is a symptom you should report to your consultant.

You should contact immediately if there is a significant deterioration in eyesight. Blurriness is a normal result in those first few days of recovery as are changes in eyesight. Driving and work that involves concentrated attention with the eyes might be difficult in those first few days.

There will be a contact lens put into your eye to help protect it during the first few days of recovery.  You should not rub your eyes for at least 5 days after the treatment.

The recommendation is to take the week after treatment off work. Do not drive in that first week.

Corneal crosslinking is a surgery, so there are the usual risks of infection and pain. These are low but not non-existent. It is also possible for there to be damage to the cornea or the epithelium.

You will probably have to change your prescription for glasses as a result of corneal crosslinking. The treatment will not remove the necessity for you to use glasses if you currently do.

It is possible for corneal crosslinking to make sight worse in the eye that is treated. This is unusual, it occurs in perhaps 3% of cases. If this does happen then the treatment is to have a corneal transplant.

For some 20% of untreated keratoconus patients the necessary treatment is a corneal transplant so the risk of non-treatment can be considered to be higher than that of corneal crosslinking. Seeing a temporary haze happens in some 100% of treatments.

A slight haze can be permanent in up to 10% of patients. There will be a significant increase in light sensitivity during the recovery period. This is not a risk as such, more of an effect.

It is important to rest the eye during this period. The increased sensitivity can mean that exposure to light levels normally happily tolerated will cause pain and or damage.

Overall the risks of keratoconus significantly degrading eyesight over time are greater than any risks from the procedure of corneal crosslinking.

The earlier the treatment is discussed and undertaken, the better it is at controlling the effects of the problem.

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