You are here:
  • Procedures / Keratoconus / CXL

CXL (Corneal Collagen Crosslinking) for keratoconus


In Collagen Crosslinking (CXL), additional chemical bonds between the collagen tissue fibres of the cornea are created by first impregnating the cornea with a yellow dye (riboflavin) and then delivering a set amount of UV light. The riboflavin absorbs the incoming light energy and acts to create the conditions necessary for new intermolecular bonds (crosslinks) to form. These additional intermolecular links stiffen and strengthen the cornea.

Current CXL techniques are more effective if the corneal skin layer is removed over a 9mm diameter central zone prior to impregnation with repeated doses of riboflavin drops. Typically it takes 5-7 days for this skin layer to regenerate. During this time, quite marked eye surface discomfort and light sensitivity is normal. You should allow one week off work to recover from CXL.

CXL is a day case procedure performed under local anaesthetic (the eye is numbed with drops). You should eat, drink and take any medication as normal on the day of surgery.


Ocular examination and review with Mr Allan
Risks and benefits
  • In around 90% of patients, CXL helps to arrest further progression of corneal shape changes associated with kerataconus.
  • Many patients also have a small improvement in the corneal shape after CXL, but continued contact lens wear or further treatment may be required to improve vision. Additional treatments may include Intracorneal Ring Segment (ICRS) implantation, wavefront or topographic Photorefractive Keratectomy (PRK) or Intraocular Collamer Lens (ICL) implantation. The main aim of CXL is to stabilise the corneal shape.
  • CXL was developed in 1998 in Switzerland. It has been used more widely over the last five years as evidence of safety and efficacy has gathered. Shape stability is improved in most patients at least in the medium term (1-5 years) but evidence of longer-term stability will not emerge for several years. Continued monitoring is recommended and repeated treatment may be required in some patients.
  • Most patients make an uncomplicated recovery from CXL. Infection, inflammation and corneal tissue thinning have been reported but these complications are uncommon (probably <1%).
  • Corneal haze occurs in 10-15% of patients. This can cloud vision and cause light sensitivity. It is usually transient, peaking in the early months after treatment and resolving after a year. Permanent loss of corneal clarity has been reported but significant visual loss is uncommon (less than 2% of patients lose two lines of vision on the testing chart whereas many patients gain vision after CXL).
  • Damage to the deeper layers of the cornea leading to loss of clarity is a theoretical risk, but should not occur if the cornea is thicker than 400 microns. CXL is possible in thinner corneas using a modified technique in which hypotonic drops are used to swell the cornea to a safe thickness during treatment.
  • CXL treatment may be more effective for patients with mild to moderate kerataconus. The risk of continued progression of corneal shape abnormality and haze after CXL is thought to be higher in patients who already have advanced kerataconus (corneal curvature >58D) at the time of CXL treatment.
  • A corneal transplant may be necessary as a result of complications from CXL. This risk is low, and should be balanced against the risk of not having treatment. Without CXL, approximately 20% of Stage II Kerataconus cases will require a corneal transplant within a decade of diagnosis. The aim of CXL is to reduce the likelihood of needing corneal transplantation.
  • 20% is an overall figure for the likelihood of progression to the stage at which a transplant is required if CXL is not performed. Documented shape deterioration (from repeat corneal scans), young age, steep corneal shape, irregular corneal shape, and non-white racial background are all risk factors for continual worsening of shape for patients with untreated keratoconus.

If you wish to arrange a preliminary private consultation, please telephone 020 7566 2156 or 07484 081815 (or from outside the UK +44 20 7566 2156 or +44 7484 081815) or email

For NHS appointments, please ask your GP to send a brief referral note, forwarding details of any optometric examination to Bruce Allan at Moorfields Eye Hospital, 162 City Rd, London EC1V 2PD.