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Crosslinking (CXL)


Keratoconus is a condition that causes the cornea, the transparent front part of the eye  to weaken, get thinner and change shape. It affects about 1 in 2,000 people. The exact cause of the condition is unknown. It's possibly passed down through the family. 

Keratoconus is one of the most common reasons for corneal transplantation in younger patients. It doesn’t usually appear until the early teens, but can occur earlier in a few patients.

Many cases of keratoconus are mild and can be managed by using contact lenses or glasses. But in some patients it can progress to the point where a corneal transplant is necessary.

| What is keratoconus?

| Treatment

Corneal collagen cross-linking (CXL) is currently the best available treatment for keratoconus. This technique uses ultraviolet (UV) light and a photosensitizer (riboflavin) to strengthen chemical bonds in the cornea.


It was first developed in Germany in 1998 and clinical trials have been in course since then. CXL consists of UV light and vitamin B2 (riboflavin) drops. Used together they cause fibers within the cornea to bond more tightly (‘cross-links’). This treatment mimics the normal age-related stiffening of the cornea.

Which types if CXL are there?

Currently there is rapid CXL and conventional CXL techniques available. 

| Conventional CXL 

The surface skin of the eye (epithelium) is removed riboflavin drops are instilled on the cornea every 5 minutes for 30 minutes. The cornea is then irradiated for 30 minutes with an ultraviolet A light emitting diode light source. During irradiation, an additional drop of riboflavin is instilled every 5 minutes.  

| Rapid CXL

Speeds this process up, delivering the same total UV energy dose in 4 minutes than could be delivered in 30 minutes. Recent research has shown that the cornea may tolerate this shorter burst of UV light better than a longer treatment period.

What happens during CXL?

CXL is performed as a day-case procedure. Although the procedure takes less than an hour, there is usually some waiting time before treatment and some further time is required for discharge instruction. So be prepared to spend up to half a day in hospital.  


The treatment is performed in an operating room, where you will be asked to lie flat on the treatment table. Anaesthetic drops are used to completely numb the surface of the eye before a small clip is placed to keep the eyelids open. The surface skin of the eye (epithelium) is gently brushed clear and riboflavin drops are applied every few minutes for 20 minutes. Following this, the ultraviolet light is shone at the eye for 4 minutes. A soft ‘bandage’ contact lens is placed on the eye at the end of procedure.

What happens after CXL?

After the anaesthetic drops wear off later that day, the eye will be gritty, red and sensitive to light for several days afterwards. You will be given eye drops to use after the procedure. The soft contact lens will remain in your eye until the surface has healed (7 days). Everyone’s experience of pain is different, with some patients reporting very little discomfort and others describing the first few days as very uncomfortable. The eyes may be light sensitive and many patients find sunglasses helpful. Your vision will be quite blurred at first, but will clear gradually over the first few weeks.

If you experience increasing pain after day 3-4, you should attend the casualty service to check for infection. But this is relatively unusual, affecting less than 1% of patients.

Which patients benefit from Cornela Cross-Linking?

The treatment is only currently available for patients with evidence that their keratoconus is deteriorating. Because of natural cross-linking, keratoconus normally stops getting worse by the mid-thirties and CXL is not normally required for older patients.


What evidence is there that it works?

Collagen cross-linking is the only treatment currently available which appears to stop progression of keratoconus. Evidence from 3 randomised clinical trials 1 year after CXL showed success in halting keratoconus progression in 97% of treated eyes, with over 45% of eyes also gaining an improvement in corneal shape. Longer-term results (up to 5 years) from a different study confirmed 100% success rate in preventing keratoconus progression. Vision is better after treatment than before in about 50% of eyes treated with CXL.

What are the risks of CXL?

In general, CXL is very safe, but like all operations the body needs time to heal and problems do occasionally occur.


About 3% of patients will lose some vision in the treated eye as a result of haze, scarring, corneal surface shape irregularity or infection. In most cases, this visual loss is potentially reversible with a corneal transplant. 

Without CXL treatment, at least 20% of all patients with keratoconus will eventually require a corneal transplant. The risk of transplantation for patients with documented disease progression is probably higher.

Do I need to take time off work or studies?

Yes. You should allow at least 1 week off while most of the surface healing occurs (2 weeks if your job involves a lot of computer work, and the treatment is being done on your best eye).


You will be putting eye drops in every hour for the first day, and then every 4 hours for the following days. Using the eye soon after surgery (e.g. reading, TV, computer) will not do any damage, but you may find it more comfortable to rest with the eyes closed early on.


You will be given an appointment the following week to check the eye is healing properly.

What should I do, or not do, after CXL?

It is important to put the eye drops in regularly as prescribed. Wash and shower normally, but try to avoid getting water in your eyes. You may exercise but should not swim before the surface of the eye has healed.


You may drive when you can read a number plate at 70 feet with both eyes open whilst wearing glasses or contact lenses as appropriate; we will check your vision in the clinic the following week to confirm if your vision is good enough to drive. It is normally safe to resume contact lens wear once the eye surface skin layer has healed. Typically this is around the end of week 2.

Let's talk about your eyes. Make an appointment now.

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