Treatment Effect and Corneal Light Scattering With 2 Corneal Cross-linking Protocols A Randomized Clinical Trial

IMPORTANCE We describe and evaluate a complementary method to indirectly quantify the treatment effect of corneal cross-linking (CXL). Additional methods to indirectly quantify the treatment effect of CXL are needed. OBJECTIVE To assess the spatial distribution and the time course of the increased corneal densitometry (corneal light backscatter) seen after CXL with riboflavin and UV-A irradiation. DESIGN, SETTING, AND PARTICIPANTS Open-label randomized clinical trial of 43 patients (60 eyes) who were 18 to 28 years of age and had progressive keratoconus and a plan to be treated with CXL at Umea University Hospital, Umea, Sweden. The patients were randomized to receive conventional CXL (n = 30) using the Dresden protocol or CXL with mechanical compression of the cornea using a flat rigid contact lens sutured to the cornea during the treatment (CRXL) (n = 30). All participants were followed up during a 6-month period from October 13, 2009, through May 31, 2012. INTERVENTIONS Corneal cross-linking according to the Dresden protocol or CRXL. MAIN OUTCOMES AND MEASURES Change in corneal densitometry after CXL and CRXL for keratoconus. RESULTS Of the original 60 eyes included, 4 had incomplete data. A densitometry increase was seen after both treatments that was deeper and more pronounced in the CXL group (difference between the groups at 1 month in the center layer, zone 0-2 mm, 5.02 grayscale units [GSU], 95% CI, 2.92-7.12 GSU; P<.001). This increase diminished with time but was still noticeable at 6 months (difference between the groups at 6 months in the center layer, zone 0-2 mm, 3.47 GSU; 95% CI, 1.72-5.23 GSU; P<.001) and was proportional to the reduction in corneal steepness (R = -0.45 and -0.56 for CXL and CRXL, respectively). CONCLUSIONS AND RELEVANCE The degree of corneal light backscatter relates to the reduction in corneal steepness after cross-linking and may become a relevant complement to other methods in evaluating the cross-linking effect, for example, when comparing different treatment regimens.