Late-Onset Deep Stromal Scarring After Riboflavin-UV-A Corneal Collagen Cross-Linking for Mild Keratoconus Riboflavin-UV-A corneal collagen cross-linking (CXL) is a new tech- nique that aims to arrest keratoco- nus progression. Riboflavin ad- sorbed to corneal stromal collagen fibers is activated by UV-A light, with the formation of cross-links be- tween collagen fibrils that confer greater corneal rigidity.1 Initial clinical experience sug- gested that the technique was safe, but stromal haze formation is a com- plication that is increasingly being recognized.2-4 Herrmann et al2 de- scribed a case of transient subepi- thelial haze that resolved with topi- cal steroids. Of greater concern, Raiskup et al3 and Mazzotta et al4 have described permanent stromal haze after CXL, with an incidence rate up to 8.6%.3 In both of these ar- ticles, the haze was relatively mild and occurred in eyes with ad- vanced keratoconus. The aim of this article is to de- scribe the clinical and in vivo con- focal microscopic findings of deep stromal scar formation after CXL in 2 patients with mild keratoconus. Methods. An ongoing trial on the safety and efficacy of CXL that com- menced in November 2008 at our center has enrolled 30 subjects to date. Briefly, subjects aged 18 years or older with progressive keratoco- nus, best-corrected visual acuity bet- ter than 20/40, and minimum cor- neal thickness of 400 mm or greater are included. Keratoconus is de- fined by 1 or more of the following signs: stromal thinning, conical pro- trusion, Fleischer ring, Vogt striae, and anterior stromal scarring. All CXL procedures are per- formed according to a standard pro- SMALL CASE SERIES tocol. Subjects are asked to discon- tinue contact lens wear 3 days before surgery and to discontinue vitamin C supplements 1 week before sur- gery. Pachymetry is performed to en- sure a thickness greater than 400 um before the epithelium is removed in several areas within a central 8- to 9-mm zone. Riboflavin/Dextran so- lution is instilled as a viscous eye drop every 2 minutes for 30 min- utes, and corneal penetration is checked by noting homogenous yel- low fluorescence in the anterior chamber on a slitlamp before pro- ceeding. The UV-A light is then fo- cused on the cornea using the UV-X illumination system (IROC, Zurich, Switzerland) for 30 minutes with continued instillation of riboflavin solution every 2 minutes. Illumina- tion intensity (3 mW/cm2) is checked with the included light me- ter prior to each treatment. After sur- gery, all subjects receive a topical an- tibiotic-steroid combination and a bandage contact lens. Confocal microscopy is per- formed using the Heidelberg Retina Tomograph III Rostock Cornea Module (Heidelberg Engineering GmbH, Dossenheim, Germany) be- fore and 3 months after surgery, with scans performed in the central 4 mm of the cornea. All study procedures are per- formed in accordance with the te- nets of the Declaration of Helsinki as revised in 1989. Written in- formed consent is obtained from the subjects, and the study has been ap- proved by the institutional review board of the