What is collagen cross-linking?
Although many current treatments can improve vision in keratoconus, they do not treat the underlying cause of the corneal weakness and distortion i.e they do not stop the progression of keratoconus. Collagen cross linking with riboflavin (commonly known as C3R) is one such treatment modality which stops propressive weakening of the cornea that occurs in keratoconus.
The one hour C3-R treatment is performed in the hospital. During the treatment, custom-made riboflavin eye drops are applied to the cornea, which is then activated by ultraviolet A light(370nm). This amazingly simple process has been shown in laboratory and clinical studies to increase the amount of collagen cross-linking in the cornea and strengthen the cornea. In published European studies, such treatments were proven safe and effective in patients.
A pilot clinical study in humans evaluated the effect of the new cross-linking method in patients with keratoconus and showed that, in all treated eyes, progression of the condition was halted. To date there are over 700 patients with more than 5 years follow-up after cross-linking treatment and some eyes have been followed for 7 years with encouraging results.
How is the treatment done?
The treatment involves removing the superficial layer (epithelium) from the surface of the cornea and then applying Riboflavin eye drops to the eye for 30 minutes. The eye is then exposed to UVA light for another 30 minutes. After the treatment, a bandage contact lens is worn for 1-3 days until the surface of the eye has healed. Antibiotic and steroid eye drops are also prescribed for a few weeks.
Who can benefit from this treatment?
It is important to understand that collagen cross-linking treatment is not a cure for keratoconus. Rather, it aims to slow or even halt the progression of the condition. After the treatment, it is expected that it will continue to be necessary to wear spectacles or contact lenses (although a change in the prescription may be required). However, it is hoped that the treatment will prevent further deterioration in vision and the need for corneal transplantation.
Thus initially the treatment would be offered only to patients in whom there is clear evidence of progression of their keratoconus. A person whose keratoconus is already so bad that it cannot be corrected by contact lenses is unlikely to gain any benefit from this treatment. In this situation a corneal transplant is usually required.
What are the risks?
There are a number of potential risks associated with this treatment although very few complications have been reported so far.
Ultraviolet light is potentially harmful to the eye .However, the dose used is designed to prevent observable damage to the sensitive cells that line the back of the cornea (endothelium) or the other delicate structures within the eye eg lens and retina. No lens opacities (cataracts) have been attributed to this treatment in European trials.
The treatment involves the scraping away of the outer layer (skin or epithelium) of the cornea. There is therefore a risk that the surface of the cornea will be slow to heal. Infection may occur which could lead to the development of corneal scarring. Antibiotics are routinely used to prevent this complication. Corneal scarring might necessitate further surgical procedures (including corneal transplantation)though this is extremely rare.
Other lesser but more common risks include:
- Inability to wear contact lenses for several weeks after the treatment.
- Changes in the shape of the cornea necessitating a refitting of a contact lens or a change in the spectacle correction.
- As is the case with any experimental treatment, there may also be long-term risks that have not yet been identified.
- The increased corneal rigidity induced by exposure to UVA and riboflavin may wear off over time and further periodic treatments may be required, raising the possibility of other side effects from repeat doses of the treatment.
A NEW FORM OF COMBINATION TREATMENT HAS BEEN INTRODUCED WHICH INVOLVES COLLAGEN CROSSLINKING AND INTACS AFTER 3-6 MONTHS. THIS TREATMENT IS KNOWN TO HALT THE PROGRESSION AND ALSO STABILIZES THE CORNEA.