Cross-Linking in Keratoconus
Keratoconus softens the corneal tissue. These changes are caused by a pathological reduction of cross-links, the chemical bonds that keep the collagen molecules bound together, in the cornea.
In fact, the connective tissue across all of our bodies are held together by cross-links: it’s what gives bodily tissue mechanical strength. We know a lot more about these cross-links today than we did 20 years ago. For example, the number of cross-links increases with age – explaining why our bodies get stiffer in their old age. This is likely to be the same reason classical keratoconus stops progressing later in life: the cornea becomes naturally cross-linked with age.
Keratokonus = reduced number of cross-links
In keratoconus, the number of cross-links is reduced as a result of the disease, and this reduces the biomechanical strength of the cornea – or in other words, weakens it. The cornea becomes thinner and thinner, making it less able to contain the pressure inside the eye, making the cornea bulges slowly forwards, eventually assuming a cone-shaped form.
Cross-Linking in Keratoconus (CXL)
Cross-linking a keratoconic cornea dramatically increases the number of cross-links in the cornea. Within a few hours, the biomechanical strength of the cornea increases by 450%. There’s a great deal of clinical experience with CXL – the first procedure was performed in 1999 (almost 20 years ago) and there has been over 1,300 peer-reviewed papers on this procedure in the manuscript to date.
CXL can be performed at any age, but we perform it most often in people aged between 6 and 60 years.
CXL treatment is divided into 3 steps: saturation of the cornea with riboflavin, UV irradiation and postoperative follow-up.
Stage 1: Saturation of the cornea with vitamin B2 (Riboflavin)
Because vitamin B2 is a large molecule, it can not easily penetrate the cornea. In classic cross-linking (i.e., the Dresden protocol) we remove around 8 mm (diameter) of the sealing layer of the cornea, the epithelium. This can be done manually, by means of an EBK (Epi-Bowman keratectomy) blade or with the excimer laser. In very rare cases, we sometimes perform an epi-on CXL (more here).
Stage 2: Irradiation with UV-A
This step is completely painless. Depending on the age, intensity of the disease, corneal thickness, speed of progression and any other factors (IVF, planned/impending pregnancy, thyroid disorder), we may choose a different intensity for the treatment of your eye.
Stage 3: Postoperative follow-up
This is extremely important because early intervention can treat any (very rare) undesirable effects immediately. Further, each person has different rates of wound healing; too intense wound healing needs to be controlled, which we are able to do.