CROSS-LINKING

Given how successful combined corneal collagen crosslinking (CXL) and excimer laser ablation has been in rehabilitating vision in ectasia patients, it’s tempting to suppose that routinely following LASIK with CXL might prevent iatrogenic ectasia. The prospect of undoing some of the corneal structural damage of LASIK, or reducing the need for careful topographic screening are also enticing – as is charging patients extra for CXL, George Kymionis MD, PhD, told the 2013 ESCRS Congress in Amsterdam.

However, the prophylactic effect of routine CXL has yet to be demonstrated, said Dr Kymionis, who has researched crosslinking and combined excimer-CXL procedures extensively at the University of Crete. Indeed, given that newer screening techniques have reduced post-LASIK ectasia rates to about one in 5,000 cases, an enormous study would be required to statistically validate the hypothesis.

On the other hand, CXL exposes patients to several complication risks, Dr Kymionis said. These include corneal scarring, anterior and posterior corneal haze, corneal infiltrates, diffuse lamellar keratitis and endothelial cell damage. Longer exposure at surgery may increase infection risk.

Also, some known crosslinking effects raise as-yet unanswered questions about its routine use, Dr Kymionis said. Potentially significant issues include synergistic refractive effects that are not always predictable; long-term refractive changes due to progressive corneal flattening after CXL; and changes in post-CXL tissue ablation rates complicating re-treatment.

The long-term effect of routine UVA exposure on stromal keratocyte loss, including the possibility of corneal melting when keratocytes repopulate, is also unknown, as are long-term effects on the conjunctiva, corneal stem cells and the crystalline lens. “For a very low incidence of complications we are exposing the patient to a lot of unknown postoperative risks,” Dr Kymionis said.

He believes there are better, proven ways to reduce the risk of post-refractive corneal ectasia. One reason post-LASIK ectasia rates are falling is that flap thickness is more controllable using femtosecond lasers, so it makes sense to use one, he noted.

Improved topography and tomography algorithms make it easier to detect abnormal corneal profiles, Dr Kymionis said. New biomechanical devices, such as the Ocular Response Analyzer (Reichert Technologies, Buffalo, NY, US) also help detect patients at higher risk. He recommends using these as well.

When a high-risk patient is identified, consider PRK or a phakic IOL instead of LASIK, or abort the procedure entirely, Dr Kymionis said. “Do not routinely perform CXL on a LASIK case until we can determine the risk and benefits.”

George Kymionis: kymionis@med.uoc.gr