 Prospective longitudinal randomized case-control study including progressive keratoconus cases is addressed to evaluate the effectiveness of collagen cross linking CXL in reducing progression of mild and moderate progressive keratoconus. Progression is based on increase in the cone apex keratometry of - 0,75 D, alteration of - 0,75 D in the spherical equivalent or increase of the anterior chamber depth on Pentacan, in a period of at least six months. All patients must be between 15 and 40 year old and are randomized and allocated in the treated or the control groups. Complete exam before and after exam included best corrected visual acuity, refraction, IOP, fundoscopy, imaging exams such as corneal computerized topographic, pentacan, orbscan, ultrasound pachymetry, esthesiometry, endothelial cell count, HRT II system confocal microscopy, optic coherence tomography VISANTE, ORA , optic coherence tomography Stratus OCT and dynamic contour tonometry . All the exams are repeated 1, 3, 6 and 12 months after the procedure. The cross linking is performed as follows: after topical anesthesia, the epithelial tissue is removed in a 8.0mm diameter area of the central cornea, the 0,1 riboflavin solution is applied every 2 min, for 30 min followed by cornea irradiation with UVA light with a wavelength of 370 nm and an irradiance of 3 mWcm2. During the irradiation, drops of the riboflavin solution is continuously applied onto the cornea every 5 min. 