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Up Front | Apr 2009

What is the Impact of CXL?

Since corneal collagen crosslinking (CXL) received the Conformité Européene (CE) Mark in Europe, there has been a flurry of activity and interest. This is a result of the excellent basic science and clinical work performed by many, including Theo Seiler, MD, PhD; Gregor Wollensak, MD; and Eberhard Spoerl, PhD; who deserve special mention.

CXL use in ophthalmology is still in its infancy. The editoris of CRST Europe would like to stress that this cover focus is an informative collection of articles highlighting a variety of aspects of CXL, starting with the academic viewpoints of Sally Hayes, PhD, and Keith M. Meek, PhD; as well as John Marshall, PhD, FRCPath, FRCOphth (Hon), and Nathaniel Knox-Cartwright, MA, MRCOphth, and progressing to articles on the variety of indications and results from relatively early clinical experience.

Keratoconus is a frequent occurrance in our patients. Apart from instructing them to avoid eye rubbing, there is little to influence its natural progression. To understand what influences the condition, we must have the proper measurements. Currently, the main measures are refractive and keratometric changes and more sophisticated topography.

The condition of keratoconus is one of abnormal elasticity, and it is this that we would ideally measure; however, unfortunately to date there is no reliable method. Corneal hysteresis measurements using deformation and ultrasound are being investigated. But because of a number of variables, absolute reliable methods and measures confined to the cornea alone are not available. CXL has been demonstrated ex vivo to favorably influence the strength of the human cornea. It has also been used in vivo with good success. This is revolutionary for keratoconus patients, as even a delay (if not absolute arrest) of the condition will markedly reduce visual morbidity as well as reduce the number who will require corneal transplants.

As illustrated in this issue's articles, one has to understand the basics of CXL before he performs the procedure. In particular, we must discredit the fallacy that adjoining collagen lamellae are crosslinked between each other. More likely, it is intrafibrillary crosslinking that takes place. Furthermore, safety considerations have yet to be elucidated fully. For instance, what effect does the procedure have on limbal stem cells? Riboflavin absorption of UV-A light is thought to protect internal ocular structures; however, there remains a potential for damage if sufficient riboflavin is not absorbed into the cornea and anterior chamber. Long term, we are still uncertain whether a need for repeat procedures will arise because of natural collagen turnover. As Farhad Hafezi, MD, reminds us, "CXL remains a relatively new method with a potential for complications that is not yet fully understood." I agree with his suggestion that valid and documented indications for the procedure should be formulated.

CRST Europe, in my biased opinion, is a phenomenal source of information in terms of current practice and innovation and, unsurprisingly, has a great following. Every so often, the publication excels above and beyond its prowess to provide a special edition that covers a topic in considerable breadth. This publication on CXL is one such issue, which I know the readership will enjoy and should keep as a point of reference. As usual, we would appreciate feedback from the readership—even if it is a short, reassuring e-mail that we are on the right track.Ên