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.
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 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 (more than 20 years ago) and there has been over 2,000 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.
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. Sometimes, we also perform an epi-on CXL.
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.
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.