Photochemical corneal collagen cross-linking for keratoconus

Photochemical corneal collagen cross-linking (CXL) with vitamin B2 and Ultraviolet (UV) light is a treatment used for keratoconus. 


Keratoconus is a condition that causes the cornea (transparent dome at the front of the eye) to get thinner and change shape, which causes reduced vision. It usually appears around puberty and progresses over the years.

Keratoconus affects about 1 in 1,750 people and occurs equally in males and females, and across all ethnic groups. In the UK, 25 out of 100 (25%) corneal transplants are done for patients affected by keratoconus.

Benefits of photochemical corneal CXL with vitamin B2 and UV light

Vitamin B2 and UV corneal (CXL) is a treatment that stabilises and strengthens the cornea, and stops the progression of keratoconus.

The treatment works for 95 to 98 out of every 100 patients with up to 6 years of follow-up care. It also improves the overall corneal shape for most patients.   

Risks of photochemical corneal CXL with vitamin B2 and UV light

This is a fairly safe treatment but as with any procedure, there are some risks associated with it.

Infection and scarring of the cornea

This happens rarely (1 in every 100 patients), and can permanently reduce your vision, which might need a corneal transplant.

Progression of the condition

This can happen in 2 to 5 in every 100 patients. Because keratoconus progresses fairly slowly, it will be a minimum of 12 months (1 year) before we will know if the procedure has been effective. Improvements in vision and corneal shape do not usually occur until 6 to 12 months after the treatment.

The risks of this procedure will be discussed with you in detail. If you have any questions about risks or would like more information, please speak to a doctor or nurse caring for you.

Other treatment options

Your doctor has recommended this treatment because your keratoconus appears to be progressing. 

There are no other treatments that have been shown to stop the progression of keratoconus. Without the treatment, your condition will probably get worse. 

We want to involve you in decisions about your care and treatment. If you decide to go ahead, you will be asked to sign a consent form. This states that understand what the treatment involves, and you agree to have it. 

Read about our consent process

Preparing for treatment

You can eat as normal before the treatment, but you should only have a light meal.

You will need to arrange for a responsible adult to accompany you to the hospital on the day of your treatment, so they can help you on your way home. They will also need to stay with you for at least 3 days after the treatment.

Please wear comfortable, loose-fitting clothing on the day of treatment. 

During the treatment

The doctor will put anaesthetic drops in your eye so that you do not feel any pain. The central corneal skin (epithelium) will be removed. Vitamin B2 drops will be applied to the eye for about 30 minutes. Once the B2 drops have soaked into the corneal stroma (thick, middle layer of the cornea), the UV light will be directed onto the cornea for about 10 minutes.

The whole treatment for 1 eye lasts 60 minutes. Usually, only 1 eye is treated at a time, with the second eye being treated a few months later.

Pain during treatment

You will not feel any pain during the treatment because of the anaesthetic drops used. Your eye will be painful for about for 24 to 48 hours after the procedure. To help relieve the pain, we will give you anaesthetic eye drops, and painkillers to take by mouth.

After treatment

You will be able to leave hospital, accompanied by a responsible adult, shortly after the treatment. 

A contact lens bandage will be placed on your eye to help with pain relief and healing. It will be removed by your doctor at your first follow-up appointment a few days after the treatment.

Your vision will be blurred for 1 to 2 weeks, and you will not be able to wear contact lenses for 2 to 3 weeks. You will be given antibiotic and anti-inflammatory eye drops to use for 2 weeks after the procedure. This is to minimise the risk of infection, and reduce the redness and inflammation in the eye.

Pain after treatment

Your eye will be painful for about 24 to 48 hours after the procedure. You will need to make sure you rest.

The pain in your eye will be worse for 12 to 18 hours, but it will gradually get better.

If you are still having symptoms after this time, you should come back to the eye department, or your nearest emergency department (A&E). 

Go to the eye department, or your nearest emergency department (A&E) immediately if:

  • your eye gets more painful 
  • your vision gets worse
  • your eye becomes more red
  • you notice pus, or discharge coming from your eye

Resuming your normal activities

You should take 10 days leave from work after your treatment. You should avoid any sports activities for 2 weeks.

It is best that someone stays with you to help you for at least 3 days after the treatment.

Follow-up appointments

A follow-up appointment for a few days after the procedure will be booked for you before you leave the hospital. It will take place in the eye department at St Thomas’ Hospital.

Resource number: 3943/VER3
Last reviewed: August 2022
Next review due: August 2025

Contact us

If you have any questions or concerns about your photochemical corneal CXL treatment at our hospitals, please contact the anterior segment secretary.

Phone: 020 7188 4331, Monday to Friday, 9am to 5pm.

Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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