Keratoconus softens the corneal tissue. This is caused by a pathological reduction of cross-links, the chemical bonds that keep the collagen molecules of the cornea bound together.
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. As a result, 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 have 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 through the epithelium — the top layer of the cornea.
In classic “Dresden protocol” cross-linking we manually remove a ~8 mm diameter region of the epithelium before applying the riboflavin.
However, advanced formulations of riboflavin now exist that can penetrate through the epithelium, meaning CXL can be performed without having to remove it. This is called epithelium-on (“Epi-on”) CXL — which should result in less pain and faster recovery times.
This step is completely painless.
A number of factors determine which UV irradiation patterns and intensities used to cross-link your cornea. These include:
• your age
• intensity of the disease
• corneal thickness, and
• speed of progression
and several other factors, such as planned IVF/impending pregnancy, thyroid disorder or estrogen modulation therapy.
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.
