When to cross-link?
Corneal cross-linking (CXL) is able to stop the progression of corneal ectsaias – not just keratoconus, but also pellucid marginal degeneration (PMD) and post-LASIK ectasia too. Generally speaking, performing CXL makes sense when the disease is still progressing. The question of when to cross-link is closely linked to the age of the patient – but other factors factor in to the decision making process too.
Our body consists, to a large extent, of connective tissue. This fabric gives our body strength – it literally keeps you body parts together.
The cornea is also made of connective tissue – principally collagen, which gets stiffer thanks to cross-linking that occurs naturally with age, and this also happens in the cornea. This stiffening can cause keratoconus disease progression to come to a halt sometime in the course of life. The older you are, the greater the probability is that keratoconus will stop progressing. Typically, keratoconus progression slows at around 35 years of age onwards – and we only rarely see cases with progressive classic keratoconus at age 60. But these are general, not absolute values. Everyone ages at a different rate; the age where keratoconus progression eventually halts varies from person to person.
This means that, in general, we do not operate on adults until progression of the disease has been clearly detected by corneal topography measurements. However, we do have a way of looking into a patient’s past visual history – old spectacles lenses and eyewear prescriptions from opticians can tell is a story. If we see historical changes in astigmatism, then this is an indication that the disease is still active.
There are a number of other crucial factors in adults.
This is likely to be an enhancing factor in the progression of keratoconus. If you rub the eyes frequently, we will check your corneas more regularly!
The female sexual organ causes connective tissue in the body to soften – and this includes the cornea. Should a patient with keratoconus become pregnant, special care needs to be taken.
Recent work, largely based on ELZA’s scientific research, has shown that thyroid hormone (particularly low levels of it, known as hypothyroidism) may also play a role in keratoconus and intensify the disease.
The story is rather different in children. Keratoconus is most prevalent in children, and the disease is most aggressive in children too. In other words, keratoconus progression in children tends to progress at tremendous speed. A large study in 2012 has already shown, that when keratoconus is detected, it is better to progress directly to CXL in children, rather than perform what’s best practice in adults (measure the cornea at repeated visits and wait for progression). This study comes from ELZA’s Medical Director, Prof. Hafezi’s research group, and showed that if a child has been diagnosed with keratoconus, the probability it being active, progressive keratoconus is 88%. In other words, 9 out of 10 children who show keratoconus will worsen if nothing is done.
Six years ago, Professor Hafezi recommended that children and adolescents should be directly cross-linked by the age of 20. Most surgeons worldwide have adopted this recommendation.