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What Is Corneal Cross-Linking for Keratoconus?

Corneal cross-linking uses riboflavin drops and UV light to stiffen the cornea and stop keratoconus worsening. It halts progression; it does not reverse it.

By Vireon Medical Editorial TeamFirst published Evidence checked through

Short answer

Corneal cross-linking (CXL) is a treatment that uses riboflavin (vitamin B2) eye drops and ultraviolet light to stiffen the cornea, the clear front window of the eye, so that keratoconus stops getting worse.1 It aims to halt the condition, not to reverse it, so most people still need glasses or contact lenses afterwards.1 Whether it is offered depends mainly on scans showing that the keratoconus is progressing, and on the thickness of the cornea and the person’s age.1

Key points

  • CXL strengthens the bonds between the collagen fibres of the cornea.
  • The main goal is to stabilise the cornea and protect future vision; any sharper vision is a bonus.
  • One treatment is usually enough; repeat treatment is uncommon.
  • NICE considers the evidence for the standard “epithelium-off” method adequate, but not for “epithelium-on” or combined versions.
  • Recovery usually involves several sore, light-sensitive days and blurred vision for a few weeks.

What keratoconus is, and why cross-linking is used

Keratoconus is a condition in which the cornea thins and bulges forwards into a cone shape. The American Academy of Ophthalmology (AAO) explains that this scatters light and causes blurred, distorted vision, often with glare and increasing short-sightedness or astigmatism (an uneven curve that blurs vision at all distances).2

Symptoms usually start in the late teens or early twenties and can worsen slowly over 10 to 20 years, often in both eyes but not always equally.2 The cause is not fully understood. Around 1 in 10 people with keratoconus has a parent with it, and eye allergies, heavy eye rubbing and some connective tissue disorders are associated with it.2

Glasses and specialist contact lenses can correct the blur but do nothing to stop the cornea changing shape. Cross-linking targets that underlying weakness. Moorfields Eye Hospital notes that without CXL, at least 20% of people with keratoconus may eventually need a corneal transplant.1

How the treatment is done

CXL is done with numbing eye drops while you are awake. In the standard “epithelium-off” method, the thin surface layer of the cornea (the epithelium) is gently brushed away so the riboflavin can soak in. Riboflavin drops are applied every few minutes for at least 10 minutes, then ultraviolet light is shone on the eye; Moorfields describes 8 minutes of light in its faster protocol.1

A soft “bandage” contact lens is placed on the eye afterwards to protect it while the surface regrows, usually for about a week.1 The riboflavin and light together create new chemical bonds between collagen fibres, which the AAO describes as stiffening the cornea and keeping it from bulging further.2

Epithelium-off vs epithelium-on cross-linking

Some centres offer “epithelium-on” (transepithelial) cross-linking, which leaves the surface layer in place. The appeal is a quicker, less painful recovery. The trade-off is that riboflavin may not reach as deep, which is why removing the epithelium is thought by some to give a stronger effect.3

FeatureEpithelium-off CXLEpithelium-on CXL
Surface layerRemoved before treatmentLeft in place
Riboflavin uptakeFaster and deeperSlower and shallower
Early recoveryPainful for several days; higher infection risk while the surface healsGenerally quicker and more comfortable
NICE view on evidenceAdequate for routine use with normal governanceInadequate; only with special arrangements or in research
Based on NICE interventional procedures guidance IPG466 and the American Optometric Association.34

The National Institute for Health and Care Excellence (NICE) says evidence on epithelium-off CXL is adequate in quality and quantity. It says evidence for epithelium-on CXL, and for “CXL-plus” procedures that combine cross-linking with other corneal treatments, is inadequate, so these should only be used with special arrangements for consent and audit, or within research.4 In the United States, the first approved cross-linking system (2016) was approved for the epithelium-off method.3

How well does it work?

In most treated eyes, it stops progression. Moorfields reports that trials show CXL halts progression in more than 90% of eyes, with a success rate of about 94% in its own patients and fewer than 1% needing a repeat.1

The strongest single trial is KERALINK, a UK randomised controlled trial in 60 young people aged 10 to 16 with progressive keratoconus. At 18 months, the cornea had progressed in 2 of 30 patients (7%) given CXL, compared with 12 of 28 (43%) given standard care alone, and uncorrected vision was better in the CXL group.5 The authors concluded that CXL should be considered as a first-line treatment in progressive disease, but that longer follow-up is needed.5

Overall, the evidence that CXL slows or halts progression is Moderate. A 2015 Cochrane systematic review found only three small randomised trials, all at high risk of bias, and rated the evidence as very low certainty at that time.6 KERALINK was published after that review and strengthened the case, although it was a single trial in a young age group.

Who may be considered for it

CXL is usually recommended when repeated corneal scans show the keratoconus is getting worse.1 Because the condition usually stops progressing by the mid-thirties, Moorfields notes that CXL is not normally needed in older patients.1 The KERALINK trial, described above, focused on young people aged 10 to 16, the group in whom progression is most closely watched.5

Corneal thickness matters too, because the ultraviolet light must not reach the deeper layers of the eye. People who cannot manage without contact lenses may still be considered if the cornea is not too thin.1 Keratoconus is also a common reason laser vision correction is not offered; see who may not be suitable for laser eye surgery.

Recovery and risks

Expect the treated eye to feel sore, gritty and sensitive to light for several days, with some pain common in the first two days. Vision is blurred at first and usually clears over the first few weeks.1 Moorfields advises most people to take at least a week off work, or two weeks if the treated eye is the better-seeing eye and the job involves a lot of screen work. Contact lenses are usually restarted around the end of the second week, and swimming should wait until the surface has healed.1

Serious problems are uncommon. Moorfields reports that fewer than 3% of patients lose some vision in the treated eye, which may improve with time, and that infection affects fewer than 1%.1 The infection risk is linked to the period when the surface layer is healing.3

When to seek medical advice

Pain that is getting worse three or four days after treatment, rather than easing, may be a sign of infection. Moorfields advises urgent attention at an accident and emergency department or eye casualty in this situation.1 Seek prompt advice too if vision drops suddenly or the eye becomes increasingly red.

Common questions

Will cross-linking improve my vision?

It might a little, but that is not its purpose. Some people see a modest improvement in corneal shape or sight, but the aim is to stop further loss.1 Most people continue to need glasses or contact lenses.

Does cross-linking hurt?

The treatment itself is done under numbing drops, but the first few days afterwards are often uncomfortable with the epithelium-off method. Pain is usually worst in the first two days and is managed with pain relief and the bandage lens.1

Are both eyes treated at once?

Often not. Each eye is judged on its own scans, since keratoconus can progress at different rates in each eye.2 Treating one eye at a time also leaves one eye seeing reasonably during recovery.

Can I fly soon after cross-linking?

The sources reviewed here do not set a specific flying restriction after cross-linking. The practical issue is being near your treating team in case of infection while the surface heals. See when you can fly after eye surgery.

Bottom line

Corneal cross-linking is a one-off treatment designed to stop progressive keratoconus from getting worse, not to restore perfect vision. The standard epithelium-off method has the best evidence behind it, at the cost of a sore first week. Whether it makes sense depends on proof of progression, corneal thickness and age.

Sources

  1. Moorfields Eye Hospital NHS Foundation Trust. Corneal cross-linking. Moorfields Eye Hospital. https://moorfields.nhs.uk/eye-conditions/keratoconus/corneal-cross-linking Accessed 5 November 2026.
  2. American Academy of Ophthalmology. What is keratoconus? AAO EyeSmart. https://www.aao.org/eye-health/diseases/what-is-keratoconus Accessed 5 November 2026.
  3. American Optometric Association. FDA approves first corneal cross-linking system for treatment. AOA; 2016. https://aoa.org/news/clinical-eye-care/fda-approves-first-corneal-cross-linking-system-for-treatment Accessed 5 November 2026.
  4. National Institute for Health and Care Excellence. Photochemical corneal collagen cross-linkage using riboflavin and ultraviolet A for keratoconus and keratectasia (IPG466). NICE. https://www.nice.org.uk/guidance/ipg466/chapter/recommendations Accessed 5 November 2026.
  5. Larkin DFP, Chowdhury K, Burr JM, et al. Effect of Corneal Cross-linking versus Standard Care on Keratoconus Progression in Young Patients: The KERALINK Randomized Controlled Trial. Ophthalmology; 2021;128(11):1516–1526. https://doi.org/10.1016/j.ophtha.2021.04.019
  6. Sykakis E, et al. Corneal collagen cross-linking for treating keratoconus. Cochrane Database of Systematic Reviews; 2015;(3):CD010621. https://doi.org/10.1002/14651858.CD010621.pub2

Article history

  • — First published.