Corneal Cross Linking for Keratoconus
Keratoconus is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape that its normal gradual curve. Keratoconus can cause substantial distortion of vision, with multiple images, streaking and sensitivity to light all often reported by the patient. It is typically diagnosed in the patient’s adolescent years and attains its most severe state between the ages of 20 and 40.
If afflicting both eyes, the deterioration in vision can affect the patient’s ability to drive a car or read normal print. In most cases, corrective contact lenses fitted by a specialist are effective enough to allow the patient to continue to drive legally and likewise function normally. Further progression of the disease may require surgery, for which several options are available, including intrastromal corneal ring segments, cross-linking and in 10-15% of cases, corneal transplantation.
Keratoconus affects around one person in a thousand; difficulties with differential diagnosis cause uncertainty as to its prevalence. It seems to occur in populations throughout the world, although it is observed more frequently in certain ethnic groups, such as South Asians. Environmental and genetic factors are considered possible causes, but the exact cause is uncertain.
Corneal Collagen Cross-Linking
This is a technique which uses UV light and a photosensitizer to strengthen chemical bonds in the cornea. The goal of the treatment is to halt progressive and irregular changes in corneal shape known as ectasia. These ectatic change are typically marked by corneal thinning and an increase in the anterior and/or posterior curvatures of the cornea, and often lead to high levels of myopia and astigmatism.
The most common form of ectasia is keratoconus. In the cornea, collagen cross-linking occurs naturally with aging. It has been hypothesized that this natural cross-linkage of collagen explains why keratoconus (corneal ectasia) often progresses most rapidly in adolescence or early adulthood but tends to stabilize in patients after middle-age.
The basis for the currently employed corneal collagen cross-linking techniques were developed in Europe by researchers at the University of Dresden in the late 1990’s. UV light was used to induce collagen cross-linking in riboflavin soaked pig and rabbit corneas via the oxidation pathway. The resultant corneas were shown to be stiffer. Human studies of UV-induced corneal cross-linking began in 2003 in Dresden, and early results were promising. The initial pilot study enrolled 16 patients with rapidly progressing keratoconus and all of the patients stopped progressing after the treatment.