Acting as the major focusing lens of the eye, the cornea is a clear dome made of hundreds of layers linked together with collagen. These collagen links may be deficient, whichleads to progressive corneal thinning and stretching. The cornea can start to bulge forward causing an irregular cone shape similar to a distorted football, thus affecting how the eye focuses images.
This is known as kerataconus, a common condition of the cornea affecting approximately 1 in 1000 people. Keratoconus normally affects both eyes, although at differing points of onset and rates of progression. It generally starts as early ones teenage years and continues until ones mid-thirties. It is thought that inheritance may play a part in the development of this condition.
Symptoms of Keratoconus
Keratoconus may be treated in its earliest stages by wearing glasses to focus images, but as the disease progresses thisbecomes ineffective. Vision typically becomes impaired at all distances, with night vision becoming particularly difficult. In addition, patients usually develop a significant distortion of vision, experiencing streaking, multiple images, and increased sensitivity to light. However, the patient rarely experiences any sensation of pain.
An ophthalmologist or optometrist can diagnose keratoconus by performing a detailed eye exam. A clinical eye exam may not be sufficient to detect keratoconus in its very earliest stages, in which case we can use a corneal topographer or a Pentacam to detect it with advanced corneal imaging. If keratoconus is present, the resulting image reveals a characteristic steepness and irregularity of the cornea.
Most patients with mild to moderate keratoconus can wear contact lenses to improve vision, but others may experience contact lens intolerance or outright failure. Regardless, contact lenses do not treat the fundamental problem: progression of disease. With the range of options being rather sparse in the past, many keratoconus patients ultimately required a corneal transplant.
Corneal collagen cross linking using ultraviolet light with riboflavin is the first treatment proven to help slow the progression of keratoconus and sometimes improve astigmatism, even in its early stages. The success of this treatment is based on its ability to lessen the abnormal elasticity of the keratoconic cornea by increasing corneal rigidity. It has been used by eye surgeons in Europe for the past ten years on hundreds of patients and the device we use to do the procudre was recently licensed by Health Canada. When corneal collagen cross linking is combined with other modalities such as Intacs corneal implants, ICLs and laser reshaping of the cornea, it can help to prevent the need for a corneal transplant.
How is Collagen Cross Linking Done?
The treatment is performed on one eye at a time, although both eyes can be treated on the same day. The treatment is conducted under sterile conditions. The eye is frozen with drops and held open for the patient. The uppermost covering layer of the cornea is removed and riboflavin drops are applied to the cornea for 30 minutes. After this, UV-A light is applied for another 30 minutes. At the end of the treatment a contact lens is placed over the cornea to aid in healing, and several drops are applied. The contact lens is left in place for several days and the patient continues the administration of drops to the eyes for several weeks. During the first 2-3 days following surgery , the front covering layer of your cornea will regenerate. You will be given a prescription for pain medication which you may use over the first few days following surgery. There is often considerable discomfort on the first night. During this period, the eye may feel very dry and irritated. The vision will be very blurry at first but will improve gradually over several weeks.
How does Collagen Cross Linking Halt the Progression of Keratoconus?
Until recently, keratoconus patients had no access to a treatment that effectively strengthened the cornea. Although the welding of the fibers that occurs during the corneal cross linking procedure has little effect on the clarity of the cornea, many European studies prove its ability to slow down and even halt the progression of keratoconus. The procedure itself is simple. First of all, vitamin B2 is applied to the cornea, followed by exposure of the cornea to ultraviolet light for a short time. The light activates molecules called free radicals that weld adjacent fibers in the cornea, much like a coiled electrical wire. It is not dissimilar to the bonding procedure that dentists use to attach materials, such as those used in fillings, to our teeth. The whole process takes about one hour.
What are the Benefits to C3R?
About 2/3 of all patients treated with collagen cross linking and riboflavin drops will have improved vision and in some cases mild regression of the steepness of their cornea. The use of collagen cross linking slows the progression of disease in all patients. Also, unlike contact lenses, collagen cross linking can stop the progress of disease and may even cause regression of disease. These results are permanent and do not involve injections or stitches. It is a relatively simple one-time, one-hour treatment with quick recovery times and long-lasting results. Most importantly, it serves as an alternative to corneal transplantation, a far more invasive procedure than C3R or Intacs Corneal rings which should only be considered after exploring all other options.
It is important to note that this collagen cross linking does not restore the cornea to a completely normal shape (similar to a soccer ball or football). Glasses and contact lenses will still be required and further treatment may be needed. In some cases, the treatment is not completely effective and the progression of the keratoconus might not be halted.
What are the Risks of Treatment?
Very few risks have been reported to date. The dose of ultraviolet light is designed to prevent damage to the cells that line the back of the cornea and other structures of the eye.
1. There have been no reports of cataracts, glaucoma or retinal injury to date.
2. A transient self limited haze will be seen in almost all patients after treatment. Usually this resolves after 6-12 months and is not visually significant.
3. Transient edema which is self limited may occur but usually resolves once the epithelium has healed.
4. The treatment may effect the measurement of intraocular pressure in the future.
5. There has been 1 case report of diffuse lamellar keratitis which was resolved with appropriate treatment.
6. There has been 1 case report of herpes simplex keratitis which was resolved with appropriate treatment.
7. It may not be effective and other forms of treatment will later be needed.
Patients will experience some discomfort which typically subsides within the first week. Some patients may not be able to wear their contact lenses for several weeks after the treatment. A new contact lens fitting may be required as well as a change in prescription.
As with any treatment, there may be long term risks which have not yet been identified. The increased corneal rigidity may wear off over time and further treatments may be required.