Advice for patients
What is keratoconus and how is it treated?
The cornea is the front transparent wall of the eye and provides two thirds of the focusing power for vision. Keratoconus (KC) is a disorder of the cornea whereby it gradually becomes thinner and more irregular in shape (astigmatism) from a relatively young age. The curvature of the cornea also increases – a process termed steepening of the cornea.
As KC progresses the vision slowly becomes more blurred. This takes months or years to do so. At some stage in the life of a patient progression may stop but this is highly variable. Progression is thought to slow down or stop partly because of age-related stiffening of the cornea.
KC normally affects both eyes, but by different amounts and at different rates of progression. If progression is rapid early then the risk of vision deteriorating at a young age is greater. As the vision deteriorates it is normal to prescribe glasses initially and then hard contact lenses when glasses are no longer adequate. In rare circumstances KC progresses to a level where contact lenses are no longer effective or manageable. This is when a corneal transplant may be necessary.
A corneal transplant usually restores good vision, however there are sometimes difficulties in getting the best vision and the recovery of vision is slow. If a corneal transplant is needed it often lasts for many years but unfortunately does not last forever.
What is Collagen Cross-linking?
It would be good to be able to stop the progression of KC soon after it is first detected. To do this may prevent the need for a corneal transplant in some people and may also make it easier to wear contact lenses or glasses. This is where a new procedure called collagen cross-linking has been effective.
Collagen cross-linking is a surgical procedure that aims to stop or slow down the progression of KC by increasing the rigidity or stiffness of the cornea. It is not a cure for keratoconus.
Collagen cross-linking of the cornea involves using the photo sensitizer riboflavin (vitamin B12) and ultraviolet light (UVA) to cause the collagen tissue of the cornea to cross-link and become stiffer. Riboflavin as drops are put in the eye to be treated for 30 minutes before illuminating the cornea with UVA light for a further 30 minutes while continuing to put in riboflavin drops. Thus the procedure takes about 1 hour (you might like to bring in some music to listen to during the procedure). In order for the riboflavin to reach the required concentration in the cornea, the surface, called the epithelium, has to be removed after local anaesthetic drops have numbed the eye. Consequently at the end of the procedure the eye is sore (even painful) for 1 – 3 days until the epithelium has healed.
How successful is Collagen Cross-linking?
Clinical studies in patients with progressive KC have shown there is a better than 90% chance of halting the progression with collagen cross-linking. In some patients it may even result in a moderate improvement in vision. This effect can be expected to last at least 5 years in follow-up studies so far, but the very long-term results are not known. It is anticipated that cross-linking will prevent further deterioration of vision and the need for corneal transplantation.
Collagen cross-linking is best done in the early stages of KC progression. KC that has progressed to an advanced stage, particularly if contact lenses are no longer helpful, is unlikely to benefit from this treatment. In this situation a corneal transplant is usually required.
Certain measurements of the eye need to be within defined ranges for collagen cross-linking to be safe and beneficial. This is largely related to the clarity, thickness and curvature of the cornea. Past eye and general health history may also be important.
After the procedure it is expected that glasses or contact lenses will still be needed to get the best vision, although the prescription may change.
What are the risks?
The major risk from collagen cross-linking is infection or scarring of the cornea, which could result in loss of some vision in the treated eye. Major loss of vision can occur but is rare. This is why only one eye is treated at a time. As described above the eye is also uncomfortable and irritable for the first few days after treatment, and the vision is blurred.
The focus of the eye usually changes and will require an upgrade in glasses or contact lenses. Some haze in the cornea always occurs but generally fades after a few months, however can be associated with fluctuating vision.
Other uncommon but nevertheless important complications that are possible after collagen cross-linking include failure to halt progression of KC, delayed epithelial healing, corneal swelling from UVA damage, contact lens intolerance, drooping of the eyelid, allergy to drops, elevated eye pressure and other unforeseen problems.
What medication will I need?
Drops will be prescribed to help prevent infection. A soft bandage contact lens will be inserted to help reduce discomfort, but local anaesthetic drops cannot be used post-operatively because they delay healing and can damage the cornea. Oral analgesics such as aspirin or paracetamol are safe to use however. A drop to reduce inflammation in the eye may also be prescribed after the epithelium has healed, which usually takes about 3 days.
A/Prof R Mills, 2014