Crosslinking: New Approach

Topography-guided individualised crosslinking may offer significant refractive advantages over conventional corneal crosslinking (CXL) in keratoconus, according to Anders Behndig MD, PhD.

“Initial results with this new treatment approach are encouraging, but obviously need to be confirmed in larger studies with longer follow-up. In this first attempt to control and improve the refractive outcomes after CXL, the effects are promising. With further fine-tuning, the method has the potential to become a valuable addition to the therapeutic arsenal in keratoconus,” Dr Behndig told delegates at the XXXIII Congress of the ESCRS in Barcelona, Spain.

Discussing the rationale for the KXL II device (Avedro, Inc.), Dr Behndig, of Umeå University Hospital, Umeå, Sweden, said there was clearly a need for more accurate and targeted CXL treatments which take account of the patient’s refractive outcome, as well as the primary need to halt the progression of the disease.

“The clinical manifestations of keratoconus can range from slight corneal asymmetry to pronounced thinning, cone formation and scarring at the more advanced stages of the disease. Despite this range, we still have only one standard CXL treatment protocol,” he said.

He explained that KXL II uses an asymmetrical treatment zone, the size and location of which is determined by the “centre of mass” of the cone as measured by Pentacam® HR (Oculus GmbH). This approach spares a 2.0mm optical zone, with energy distribution determined by the maximum keratometry reading (Kmax) ranging from 7.2 to 15J/cm2.

The system uses programmable and customisable illumination patterns with real-time eye tracking designed to enhance the refractive improvement after CXL.

In Dr Behndig’s ongoing study, which started in March 2014, 50 eyes were randomised between KXL II individualised treatment and conventional CXL, with all 25 eyes treated in both groups.

The spherical refraction showed improvement at six months after KXL II. Cylinder was also reduced in the KXL II treated patients but the difference was not statistically significant. Uncorrected visual acuity (UCVA) was worse at one month in CXL treated eyes, noted Dr Behndig.

“This is not uncommon in conventional crosslinking, but we did not see the same reduction in the KXL II treated eyes. This likely owes to the fact that the treatment spares the 2.0mm optical zone,” he said.

A statistically significant improvement in UCVA was also attained in the KXL II group compared to CXL treated patients at three and six months.

Corneal asymmetry as measured by saggital curvature maps showed enhanced inferior corneal flattening and reduction in Kmax in KXL II patients compared to those treated with conventional CXL. No differences in endothelial cell count were seen between the two treatments.

Anders Behndig: anders.behndig@umu.se