COLLAGEN CROSS LINKING
What is Corneal Collagen Cross Linking?
Corneal Collagen Cross-linking with Riboflavin (also known as C3R) has been shown to strengthen the weak corneal structure. The cornea is made up of many layers of collagen arranged in a very regular pattern. These layers of collagen are called the stromal lamellae. The collagen fibres of neighbouring layers are linked together to provide strength to the cornea. In conditions where the cornea is abnormally weak, such as keratoconus, there are fewer of these links and the result is bulging of the cornea. C3R works by increasing collagen cross-linking.
The fibrils of the keratoconus cornea lose their ability to link to each other (above, left). C3R treatment causes more cross linking of the fibrils, making the cornea stronger.
A healthy eye (fig. A) is more spherical in shape, allowing an image to come into focus clearly. The cornea of an eye with keratoconus (fig. B) bulges outward, creating a cone-like shape and distorted vision.
Keratoconus is normally treated with rigid contact lenses to reshape and flatten the pronounced curve of the bulging cornea and to improve vision. A proper lens fit is crucial to obtain adequate vision and wearing comfort. Poorly fitting or outdated contact lenses can be uncomfortable and lead to significant discomfort, corneal abrasions, scarring or infection.
Keratoconus normally affects both eyes, although at differing points of onset and rates of progression. In most people keratoconus begins during their teenage years and progresses at varying rates until stabilizing in their 30s or 40s. Although keratoconus rarely results in total blindness, 20% of all patients will at some time need to undergo a corneal transplant. This can be either because of corneal scarring that prevents useful vision, or because of intolerable side effects related to use of contact lenses.
However, corneal transplantation is a major undertaking with a prolonged recovery time. Although the final result is often favourable in keratoconus, it should be considered a last resort.
Fortunately, there are two new methods to treat keratoconus that are much less invasive than a corneal transplant: INTACS and CXL.
Corneal Collagen Crosslinking
As with any surgical procedure, there are risks of which you must be aware. Your doctor will explain these risks to you and ensure that you understand them completely. You will be given time to discuss all issues to your satisfaction.
- Corneal Ecstasia
- The Procedure
- Suitable For All?
- After The Operation
- Are There Risks?
- Added Advantage
Corneal ectasia is a condition resembling keratoconus but comes from a different origin. Almost invariably the cause is refractive eye surgery that has resulted in a cornea that is too thin or too weak to withstand the normal internal pressure of the eye. This can cause expansion or distension of the cornea, leading to increased myopia. Most of the time a special gas permeable contact lens will be needed to restore vision. C3R can be used in the same way as for keratoconus.
The cross-linking treatment is an outpatient procedure. During the treatment, custom-made riboflavin eye drops are applied to the cornea over a 30-minute period. The riboflavin becomes well absorbed into the cornea and also enters the fluid in the front part of the eye. This is essential because the next stage of the treatment involves a controlled exposure of the eye to ultraviolet (UV) light for 30 minutes. The riboflavin molecule is very good at absorbing UV light. This means that the riboflavin in the cornea is activated by UV light and the riboflavin inside the eye protects the internal structures (such as the lens) from the effects of UV light. This simple process has been shown to increase the amount of collagen cross-linking in the cornea and so strengthen the cornea.
Is C3R suitable for all keratoconus patients? C3R is a relatively new treatment and its place in the treatment of keratoconus is still being defined. This will become more apparent as more people are treated around the world and the results of these treatments are published. To date, the published literature suggests that C3R is most suited to patients with progressive keratoconus. That means patients whose glasses or contact lens prescription is changing quite frequently, or whose vision is becoming worse despite using contact lenses, or whose corneal topography maps show clear progression of keratoconus.
What happens after the operation? You will have a contact lens bandage on your eye for a few days, and you will be asked to put drops in your eyes for a few weeks. The shape of the cornea will typically take 3 months (or longer) to stabilise and during this time your vision may fluctuate. Only once the cornea has become stable should you consider glasses or contact lenses for definitive correction of any residual refractive error. Some people choose to seek temporary glasses or contact lenses during the recovery period.
What are the risks? These are uncommon but may include: Corneal infection, reduced visual acuity, and a reduced ability to wear hard contact lenses. In the event of inability to wear a hard contact lens, vision may have to be corrected by glasses or a soft contact lens and the best-corrected visual acuity may be less than that before C3R treatment.
Because the cornea is much stronger after C3R treatment, some surgeons are correcting any residual refractive error by using the excimer laser to perform laser vision correction. This is usually avoided in keratoconus patients because of the unacceptably high risk of causing corneal ectasia (as described above). However, laser vision correction seems to carry much less risk if performed after C3R.
C3R strengthens the cornea and halts the progression of keratoconus and corneal ectasia. It may be used alone, or in conjunction with other treatments such as INTACS or excimer laser vision correction or phakic intraocular lenses, to produce the optimum visual result (see the relevant iLase information leaflets). When the cornea has stabilised, glasses or contact lenses may be required to provide the best visual outcome.