The original Dresden protocol allows CXL to be performed safely when the thickness of the cornea is 400 μm or higher. However, in advanced cases of keratoconus, pellucid marginal degeneration and post-LASIK ectasia, the cornea may be thinner.
One way to treat such a cornea nonetheless is the use of hypo-osmolar riboflavin. This special vitamin B2 causes the cornea to absorb water and swell. This technique was developed in 2007 and published in 2009 with Prof. Hafezi as first author. Since then, this application has become a global standard.
Zurich, Switzerland: A 26-year-old patient is being treated with epi-off CXL. After removal of the epithelium and application of “normal” iso-osmolar riboflavin, the corneal thickness is 325 microns; too little to do a safe CXL. In a second step, we used hypo-osmolar riboflavin. After 10 more minutes, the cornea had “swollen” to 407 microns, and the CXL could be performed safely.
The treatment of extremely thin corneas requires a lot of experience as many factors have to be considered – from how often the vitamin B2 is applied, to how long the speculum is left open. Our experience is one of the longest in the world and allows us to safely perform a CXL on thin corneas (and thicker corneas too!).
A number of strategies have been developed to treat very thin corneas since 2009. ELZA’s Medical Director, Farhad Hafezi, has helped to reivew these techniques (see posts below), including contact lens-assisted CXL (CACXL) and the Epithelial Island Technique. Which technique is chosen must be carefully considered on a case-by-case basis.
In addition, the research group led by Professor Hafezi is in charge of developing new techniques that are tailored to the individual corneal thickness. In the future it will be possible to treat corneas of less than 300 μm using CXL, without swelling the cornea first.