EyeWorld India December 2017 Issue

A look at applications for crosslinking beyond keratoconus C ollagen crosslinking has already established its value in its ability to halt progressive kera- toconus and strengthen corneas weakened by post-refractive sur- gery ectasia. The quality of vision is not directly addressed though with the standard Dresden proto- col, whose main purpose is simply biomechanical strengthening. However, research continues to progress on various fronts as to the potential refractive capa- bilities of crosslinking, including customized crosslinking for kera- toconus to promote more visual improvement, LASIK combined with crosslinking to strengthen the cornea, and crosslinking for the correction of refractive error. Refractive opportunities for crosslinking by Liz Hillman EyeWorld Staff Writer AT A GLANCE • Collagen crosslinking is best known for its ability to strengthen progressive keratoconic and ectatic corneas, but researchers and clinicians see refractive possibilities as well. • Customized crosslinking— targeting treatment to the area of most corneal weakness—is showing promise in improving visual outcomes. • LASIK combined with crosslinking has been shown to improve refractive stability. • Crosslinking is also making strides in the correction of low myopia, hyperopia, and astigmatism. Customized crosslinking Topography-guided crosslink- ing, zonal crosslinking, custom- ized crosslinking: It goes by many names, but in short it describes the idea of targeting crosslinking treatment to the weakest area of the cornea. William Dupps, MD, PhD , Cleveland Clinic, Cleveland, led studies that modeled this idea, building on his group’s research ex- ploring the biomechanical origins of keratoconus. 1 “The premise is there is a weak- ening that occurs in the cornea that progresses over time,” Dr. Dupps explained. Using clinical tomogra- phy of a patient’s eyes—one with keratoconus, the other without—Dr. Dupps said they created a vir- tual eye based on the real patient’s corneal shape. In the unaffected eye model, they weakened a point on the cornea and saw curvature increase. “It developed a cone that was very similar to the one that had already manifested in the patient’s other eye,” he said. From there, the next step was to study how to approach therapy. Dr. Dupps said they researched how different treatments changed stiff- ness and thus corneal shape. In the model of an eye with a more central cone and another with an off-center cone, they looked at the differences in response using the standard 9 mm global treatment vs. a more fo- cal, or zonal, treatment centered on the steepest point. “We found that in the few cases we simulated, it predicted we would produce more than two times the amount of flattening of the steep- est portion of the cone compared to the standard treatment. Because this model incorporates the full 3-D shape of the cornea, we can pull out metrics that relate to the opti- cal quality of vision. We computed aberrations like coma and spheri- cal aberration and saw much larger decreases in coma with a zonal approach, which is the main aber- ration in keratoconus that we think degrades vision. “The take-home was that we should continue to explore the potential of more customized treat- ments to not only stabilize the dis- ease, but in some cases to achieve more optical rehabilitation than we could with a standard treatment,” Dr. Dupps said. This research has moved from the theoretical/model domain into some clinical cases. Matthias Elling, MD , senior physician, Ruhr University Bochum, Bochum, Germany, pointed to research published in 2016 by Seiler et al. that found that 37% of eyes in the continued on page 46 September 2017 Dec EWAP SECONDARY FEATURE 45 Dr. Elling and his group perform epi-on refractive crosslinking (PiXL) with an oxygen supply to boost its effect. The patient wears special oxygen goggles, and in the epi- thelial prep stage, a ribo avin-soaked sponge is applied to the treatment area before starting ribo avin drops. This procedure uses a pulsed ultraviolet light. Source: Matthias Elling, MD