How Good Is The Corneal Cross Linking Success Rate?
Can we cure people of keratoconus? We've come a long way in how we treat progressive weakening of the cornea with keratoconus. While we can't cure or reverse keratoconus, corneal cross linking can be done to prevent it from getting worse.
Corneal cross linking is a very successful procedure to prevent the progression of keratoconus. When evaluated over the long term, the success rate is approximately 95% to prevent the keratoconus from getting worse.
Some patients will have less success than others. For instance, younger patients and those with more severe keratoconus have a slightly less success rate. But that is simply if we are talking about stopping progression completely.
What Defines Success?
Keratoconus is a progressive condition. Gradually over time, the cornea weakens and changes shape. As the cornea changes shape, first the prescription of the eye changes; then the amount of astigmatism increases; and finally, the abnormal shape of the cornea distorts the vision and prevents it from being able to be fully corrected with glasses and contact lenses.
Cross linking is designed to halt the progression of keratoconus. While it can also lead to some improvement in the abnormal shape change of the cornea, the primary goal of cross linking is to prevent it from getting worse.
While slowing the progression of keratoconus is better than nothing and can be considered some form of success, the big prize of cross linking is to prevent any progression altogether. Thus, an optimal way to measure the success of corneal cross linking is to see what are the odds that the keratoconus will continue to progress or get worse after the procedure.
Long Term Success
Here's the thing, progression of keratoconus doesn't happen overnight. In fact, it can take years for any progression to happen. Thus, to most accurately measure the success of keratoconus, we must evaluate patients years and years out from their corneal cross linking.
Surprisingly, there is little data out there on the long term success of corneal cross linking for keratoconus. Granted, it isn't exactly easy to have a long-term study. To really evaluate the success, we want to see what happens over almost a decade after corneal cross linking. There must be enough patients to follow and the hardest part is reliable enough follow-up over years and years.
Fortunately, we do have some long term data to determine the estimated success of corneal cross linking! This includes studies all the way up to 10 years of followup after corneal cross linking. 
So what do we see?
In the long term, corneal cross linking is approximately 95% effective in stopping the progression of keratoconus.
While not 100%, that still is pretty successful.
Especially since the alternative (not treating with corneal cross linking) has a very high risk of progression of keratoconus.
Who Is At Risk Of Progressing?
Not everyone with keratoconus is at a high risk of progression. This is true before corneal cross linking and is true after corneal cross linking as well.
In general, patients with severe or aggressive keratoconus have a higher chance that their keratoconus can get worse - even after corneal cross linking. Cross linking still is helpful, but it is less likely to completely stop the progression compared to someone with less advanced keratoconus.
Gradually over time, the corneal actually becomes naturally cross linked. Because of this, when keratoconus develops in younger patients, it is often more severe than in older patients. As a result, keratoconus can progress much quicker in the 20s than in the 30s or 40s. Once in the 40s and beyond, keratoconus tends to "burn itself out" and is much less likely to progress. The cornea has become naturally cross linked.
So if you need corneal cross linking at a young age, you are at a greater risk of having progression in the future.
When we look at the long term success rate of corneal cross linking in kids, it is less than adults. Kids are younger with less naturally cross linked corneas. Thus, corneal cross linking has about a 75% chance of stopping progression of keratoconus for good in children. Still good, but not quite as good as what we see in the long term studies for adults.
Thus, the older you are when you have cross linking, the greater the success rate.
A similar situation exists for those who have severe keratoconus. As the keratoconus gets worse, the cornea becomes steeper and thinner.
Having a steeper and thinner cornea, reduces the success rate of corneal cross linking.
Being diagnosed and treated for keratoconus at an early stage before things get worse leads to the best outcome; not only for corneal cross linking, but also for vision as well.
Rubbing the eyes
In most cases, the cornea doesn't change on its own. Something must weaken it over time. The biggest risk factor identified for the development of keratoconus is rubbing the eyes. Rubbing the eyes puts pressure on the cornea and causes it to weaken over time.
It's important after corneal cross linking to change these habits. Continued stress on the cornea can cause the keratoconus to continue to progress.
If Keratoconus Progresses After Cross Linking
Because corneal cross linking isn't 100% effective, it is important to have regular eye exams to screen for any changes.
So what happens if the keratoconus progresses even despite being treated with corneal cross linking? Well, cross linking can be repeated.
Progression despite cross linking indicates very aggressive and severe keratoconus. But a repeat cross linking treatment can be very effective in preventing further progression. And while still not 100% effective, can still be a better option to try to avoid more advanced and riskier surgeries to treat the keratoconus.
Corneal cross linking successfully prevents progression of keratoconus approximately 95% of the time. While not perfect, it still is a dramatic improvement over the alternative of doing nothing. Having more severe keratoconus, having a younger age or rubbing your eyes after cross linking can decrease the success rate. But if the keratoconus progresses, cross linking can be repeated to improve the success rate.
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