Ophthalmologists at University Hospital in Dresden, Germany, have reported long-lasting effectiveness of corneal collagen cross-linking (CXL) in halting progression of keratoconus.1
Treatment benefits. CXL significantly reduced the maximum and minimum corneal curvatures, as well as the curvature at the apex, in eyes with progressive keratoconus. These benefits endured in most eyes after 10 years. “Until now, nobody knew how long the positive effect of the CXL procedure would last,” said lead author Frederik Raiskup, MD, PhD, FEBO.
Although keratoplasty remains the definitive treatment for advanced keratoconus, this study adds to a body of literature suggesting that CXL is a promising, less invasive therapeutic alternative to more costly and complex corneal transplantation. (At time of press, CXL was not approved in the United States, but an FDA ruling on one system was expected in March.)
In CXL, the corneal stroma is exposed to riboflavin (vitamin B2) and ultraviolet light, and the ensuing photochemical reaction strengthens and stabilizes corneal stromal collagen fibers.
Indications and cautions. CXL is indicated for keratoconus patients who have visual acuity “that allows good functioning in daily life” and also have solid evidence of disease progression, Dr. Raiskup said.
Additionally, to prevent damage to the corneal endothelium, central corneal thickness should be at least 400 μm after removal of the epithelium during the treatment. In this study, in which mean corneal thickness was 488 μm, no clinical signs of endothelial decompensation were apparent, and endothelial cell counts remained constant.
Significant study findings. The retrospective interventional case series involved 24 progressive keratoconus patients (34 eyes), with a mean age of 28.4 years. Preoperatively, five eyes (14.7 percent) were in an advanced stage of keratoconus, showing corneal scarring; nevertheless, all eyes still had good corrected distance visual acuity (CDVA).
Among the statistically significant results at 10 years compared with baseline:
- The mean apical keratometry value decreased from 61.5 D to 55.3 D.
- Mean astigmatism was reduced from 5.7 D to 4.0 D.
- Mean CDVA improved from 0.40 to 0.26 logMAR; this outcome was attributed to a reduction in astigmatism and corneal distortion and to a better fit of hard contact lenses.
Retreatment is possible. If progression of ectasia resumes, CXL can be repeated, as long as CDVA is still good, said Dr. Raiskup. In this study, two eyes needed retreatment—one after five years, the other after 10—due to increases in the K value following a period of long-term stability. At
baseline, these two eyes had maximum K values higher than 58 D and thinner corneas, which the authors believe predisposed them to further progression. In both cases, retreatment stabilized progression and did not create additional side effects compared with the initial treatment.
Complications. No serious complications occurred, although one eye developed a permanent stromal corneal scar that limited visual acuity following treatment. The anterior stroma in 13 eyes showed a persistent haze at 10 years, but it did not affect the CDVA.
The benefit of aging. The enduring effect of CXL was something of a surprise, Dr. Raiskup said. It may be attributable, in part, to the natural stiffening of the cornea that occurs over time. “There is an ongoing ‘crosslinking’ process in all of the tissues in our body,” he said. “With age, collagen in the ectatic cornea will become naturally stiffer.”
Given this natural stiffening process, in combination with effective CXL therapy that “overlaps” the very active stage of corneal ectasia, the probability is high that the majority of suitable candidates will remain stable after the first treatment, Dr. Raiskup said.
1 Raiskup F et al. J Cataract Refract Surg. 2015;41(1):41-46.
Dr. Raiskup reports no related financial interest.
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