Dr Andrew Apel

MB, BS (Qld), FRANZCO

Corneal Collagen Cross-linking with Riboflavin and UVA

Collagen is one of the basic building blocks of our bodies. Collagen provides tissue with different characteristics in different parts of the body. In our ears it provides a flexible tissue to form the lobes, at the tip of our noses it provides a more rigid shape, and in the eye it provides the rigidity to form the eye into its stable round shape. The different types of collagen are created due to differences in the connections between the molecules. These connections are called cross-links. The more cross-links there are the more rigid the tissue.

In keratoconus, there is a deficiency in the normal processes that generate the cross-links. This means that the collagen doesn’t lock together efficiently, and can move relative to the surrounding tissue. This allows for a central weakness in the cornea, resulting in the bulging effect that is observed in keratoconus.

There is now a technique to artificially create more cross-links to increase the stability of the keratoconic cornea. This reduces progression of the disease, and in some cases causes a regression of its effects.

The Treatment

The treatment involves using ultraviolet light waves to create the cross-links in the surface layers of collagen in the cornea. Riboflavin, vitamin B2, is used to absorb the ultraviolet light and create a safety barrier to protect the inside of the eye. This absorption concentrates the effects of the ultraviolet light in the surface layers of collagen, causing cross-links to form and stiffening the cornea. Without the riboflavin much of the ultraviolet light would pass through these layers without creating the desired effect.

To expose the surface layers of the collagen the procedure begins with the removal of outer cells of the cornea or epithelium. This is performed under local anaesthesia.

Following the removal of the epithelium the riboflavin is applied and left to permeate the tissues for approximately 30 minutes. The riboflavin is a bright yellow colour and this allows its penetration to be monitored. Once appropriate penetration is achieved the ultraviolet light source is switched on. The riboflavin is re-applied every five minutes with a total exposure time to ultraviolet light of 30 minutes. The total dose of ultraviolet administered is similar to walking around in the midday sun without wearing sunglasses.

What you will experience

Prior to the procedure you will be asked to undertake a series of measurements to ascertain your suitability. This may require several attendances to collect all of this information. The measurements are to demonstrate that your keratoconus is definitely progressing, and that your cornea is thick enough to undertake the procedure.

On the day of the procedure you will be asked to have some antiinflammatory medication several hours prior to the treatment to prepare your eye for the treatment. The local anaesthetic is administered using eye drops. The removal of the surface cells is performed by the ophthalmologist and will take only a few minutes.

The treatment is undertaken with you lying down. The riboflavin is administered as eye drops drawn up into a syringe. The ultraviolet device is positioned one centimetre from your eye during the treatment. You are required to maintain the treatment position with your eye looking straight towards the device to align the ultraviolet light with your cornea. To assist you with this a device will be used to hold your eyelids open for you.

Following the treatment a contact lens will be applied to your eye to assist with comfort. However, you should expect some significant discomfort or pain for up to three or four days following the treatment. During this time the epithelium that has been removed will grow back and the corneal nerve endings can be stimulated until this is complete. You will be advised on appropriate methods of pain relief during this time.

Following the treatment you will need to avoid dusty and dirty conditions until the surface of your eye has healed. You will not be able to swim during this time. Until the surface of your eye heals your vision will be blurred in the treated eye. This may mean that you will need time off work or study. Your vision may be blurred for several weeks after treatment.

Once the eye has healed you will be asked to attend regular post-operative follow-up appointments. These will be conducted over several years to allow for the monitoring of the procedure.

Risks

As with all procedures there are potential risks for this procedure.

  • There is a risk that there will be no effect from the treatment
  • There is a low risk that vision may be worse after the treatment
  • There is a risk of infection of the abrasion that is created by removing the cornea epithelium. The consequences of such an infection can include a permanent loss of vision.
  • There will be pain and discomfort for the patient following the procedure
  • There will be a yellow discoloration of the treated cornea for a period of time following the procedure that may be visible to others.
  • There will be a period of blurred vision during the recovery period that may last for several weeks or months.
  • There is a rare possibility of an allergic anaphylaxis reaction to the riboflavin