What you need to know about corneal cross-linking

By Dr Alex Ioannidis

1. What is corneal cross-linking?

Corneal cross-linking is a treatment that uses a biochemical reaction to mechanically strengthen and stiffen the cornea. It is used to stop the progression of Corneal ectasia, which is when the corneal tissue weakens and bulges, thus losing its normal dome-like shape. Vision changes can include blurred vision, sensitivity to light and glare/halos at night. The most common form of corneal ectasia treated by corneal cross-linking is that caused by keratoconus.

2. How does corneal cross-linking work?

Cross-linking creates new bonds between collagen fibres in the cornea. The result is a cornea that is stiffer and more resistant to any change in its shape.

3. What does corneal cross-linking achieve?

The aim of the treatment is to stabilise the condition and prevent it from getting worse. Patients should note that it is not possible to reverse any changes that have already occurred.

 4. How is corneal cross-linking performed?

The top layer of the cornea (the epithelium) is first disrupted, either by removing it (called the epithelium-off protocol – see Q5) or by weakening it (called the epithelium-on protocol – see Q6). Riboflavin (vitamin B2) is then applied to the eye in the form of drops and the eye is exposed to UV light – the resultant biochemical reaction creates new bonds between collagen fibres in the corneal tissue. The UV light is delivered in such a way that only the superficial layers of the eye are exposed, thus protecting deeper structures.

5. What is epithelium-off or ‘epi-off’ cross-linking?

Also known as the ‘Dresden Protocol’, this is the standard technique and has been studied the most. The treatment is performed as an outpatient procedure and takes approximately one hour. Under local anaesthesia, the surface layer of the cornea (the epithelium) is gently removed with a soft cotton bud. The cornea is then treated in two stages with the riboflavin drops and the UV light to create the bonds. The level of pain is minimal during the procedure. A thin bandage contact lens is placed on the eye at the end for 24–72 hours, depending on the individual healing response. Patients are provided with oral pain relief and antibiotics to take home, and most recover quickly with minimal discomfort.

 6. What is epithelium-on or ‘epi-on’ cross-linking?

This is a variation of the traditional ‘epi-off’ method/Dresden Protocol (see Q5), where the surface layer of the cornea (the epithelium) is left intact. There is some clinical evidence that this technique is also effective and can be reserved for patients with thinner corneas who don’t qualify for the Dresden Protocol. However, it is important to note that there is less long-term data available on the efficacy of this cross-linking technique.

7. How effective is corneal cross-linking?

It is very effective – the success rate is more than 95% for an ‘epi-off’ treatment. In the remaining 5% of patients where there is further progression or change, a second treatment may be required. There is also the option to perform corneal transplantation (keratoplasty) at any stage – in other words, cross-linking does not preclude other treatment options.

8. Can both eyes be treated at the same time?

Currently with the traditional ‘epi-off’ treatment, I recommend treating one eye at a time. This is because there is a small risk of infection, as there is with any surgical procedure on the cornea.

9. Can children be treated with corneal cross-linking?

I have treated children in the past, but this requires a general anaesthetic and is best done in the operating theatre because it is difficult to keep young children still enough to perform the procedure safely.

10. Are there alternatives to corneal cross-linking?

The current answer is no – cross-linking is the only method that has been shown to stop the progression of keratoconus. Corneal transplantation (keratoplasty) is the other option and is usually reserved for advanced cases where vision has reduced considerably. Transplantation involves removing the diseased corneal tissue and replacing it with a donor cornea. This procedure has its own risks and, in some cases, the keratoconus can return after many years. Click here for more information.

11. What are the risks and complications of corneal cross-linking?

As with any surgical procedure, there is a small risk of infection. The procedure does not cause bleeding of the eye because affected corneas do not have a blood supply. The UV light is not very strong and only penetrates the cornea, not deeper structures of the eye. Riboflavin (vitamin B2) is a natural compound that is found in our diet, for example corn flakes.

12. Who can receive corneal cross-linking treatment?

With the latest technological advances, we are able to use cross-linking to treat many more patients with keratoconus than before. It is best to treat patients early, before the disease has progressed and reduced vision substantially and/or caused significant thinning of the cornea. Cross-linking is less likely to work in patients with thinner corneas.

Read more about corneal cross-linking here.

All medical and surgical procedures have potential complications. You should check with your ophthalmologist before proceeding.