The concept that collagen cross-linking can slow, halt or even reverse the progression of cone cornea is gaining acceptance. It has been performed for 5 to 10 years in Europe, North America, Asia and around the world, and is gaining popularity in the United States, where it is now undergoing some FDA clinical trials. One of the controversial issues is at what age should the procedure be done? There is no definitive answer as to the minimum age, but the consensus seems to be that as long as there is evidence of progression of the cone cornea, it makes sense to perform this treatment. 10,12,15 years of age have all been discussed. The upper age limit is again unclear, but 35-50 years may be preferable, as cone corneas do not usually progress after that. Another controversy is whether there is a cut-off for severity? There are no exact numbers to judge, but if a patient’s corneal curvature measurements are very high, it is likely that collagen cross-linking is no longer appropriate. Another controversy is whether to preserve the epithelium before riboflavin treatment. At Cornea Specialty Days, Theo Seiler recommends de-epithelialization. In the last 5-10 years, collagen cross-linking has typically been treated with UV light for 30 minutes, so is it possible to increase the intensity of the UV light and decrease the treatment time? At the Wills Eye Institute, part of the FDA trial is being studied in this regard, using 3 different intensities and durations of UV treatment.