Keratoconus is a bilateral non-inflammatory disease .One of its characteristics is reduction of biomechanical strength of cornea and stromal thinning , which gradually decreases corneal thickness and induces  irregular astigmatism , myopia , corneal scaring, andreduction of visual acuity.⁽¹⁾For early stages of keratoconus , one would use spectacles and contact lenses though the progression of the disease can lead to irregular astigmatism or corneal scaring, leaving no other option but corneal transplantation in about 20% of patients.⁽²⁾Corneal transplantation is an expensive procedure with many complications such as high astigmatism and graft rejection;  hence, seeking for a way to halt this progressive disease seems to be of crucial importance.⁽³⁾
For more than a decade, corneal cross-linking  (CXL)   has been considered as the only method for improvingcorneal biomechanical power.⁽⁴⁾Corneal collagen cross-linking (CXL) is a low-invasive treatment aimed to improve biomechanical stability in eyes with keratectasia.⁽⁵⁾
The “standard CXL protocol" described by Wollensak and colleagues includes removal of the corneal epithelium in a diameter of 9 mm , followed by saturation of the corneal stroma using 0.1% isotonic riboflavin solution in 20% dextran.⁽⁶⁾This procedure is proved to be effective in increasing corneal stiffness , stabilization of keratoconus , and in some cases in improving the refractive and topographic features.Even so, the epithelial removal may lead to serious complications that include infection⁽⁷⁾,stromal haze ⁽⁸⁾, and corneal melting ⁽⁹⁾in addition to severe pain and decrease in vision occurring during the first days after the treatment.To avoid such complications, Boxer Wachler et al. suggested a modification of the technique by keeping the epithelium intact (epithelium-on or transepithelial CXL) ⁽¹⁰⁾.In this study, we sought to compare keratoconus indices before and after crosslinking either epi-off or epi-on CXL by Pentacam criteria.