Transepithelial CXL (performed without epithelial removal) seem to have similar clinical effect on keratoconic eyes compared to the standard CXL (which includes epithelial removal). The current study attempts to prove that hypothesis.

A prospective, controlled, randomized, contralateral trial, will involve one eye of the patient to be treated with transepithelial CXL, while the control eye will be treated with the standard CXL. Totally 20 patients (age >18 and <40 years) referred by an ophthalmologist to the eye department of the University Hospital North Norway for CXL treatment of bilateral progressive keratoconus, will be recruited.

CXL appears to hinder the development of keratoconus by strengthening the cross-bindings in the corneal stroma with a resultant increase in corneal biomechanical strength of up to 300%. The method was introduced in the mid-nineties and has been approved for use in the EU countries since 2007. Standard treatment protocol, involving the removal of the corneal epithelium before the Riboflavin application, has been used. In order to avoid potential complications following removal of the epithelium (infection, delayed healing, scar formation, as well as discomfort and pain), a modified procedure where the epithelium is kept intact, so called transepithelial CXL, has been suggested. According to the preliminary results of the published retrospective studies, no significant difference in the clinical effect between the standard CXL with epithelial removal and the transepithelial CXL was found.

Inclusion Criteria:

• Documented keratoconus progression in both eyes during the last 12 months before the treatment - decrease in best spectacle-corrected visual acuity (BSCVA) and/or increase in cornea curvature or asymmetry
• Corneal thickness ≥400μm at the thinnest point
• Age range from 18 to 40
• Amsler-Krumeich classification graded stage I to III

Exclusion Criteria:

• Corneal thickness <400μm at the thinnest point
• History of viral keratitis
• Severe dry eye
• Concurrent corneal infections
• Previous ocular surgery
• Hard contact lens wear for ≤4 weeks before baseline examination