Corneal collagen crosslinking (CXL) has been proposed as an effective method of reducing progression of both keratoconus and corneal ectasia after surgery, as well as possibly decreasing the steepness of the cornea in these pathologies. During previous studies of the CXL procedure, the surface epithelial cells have been removed. Transepithelial crosslinking in which the epithelium is not removed has been proposed to offer a number of advantages over traditional crosslinking including an increased safety profile by reducing the risk for infection as no epithelial barrier will be broken, faster visual recovery and improved patient comfort in the early postoperative healing period.

The objective of this study is to investigate the difference between two regimens of transepithelial crosslinking. The study will compare two riboflavin dosing regimens during the crosslinking procedure. The primary objective of this study is to evaluate the safety and efficacy of transepithelial corneal collagen crosslinking performed with riboflavin 0.1% for reducing corneal curvature. Safety and efficacy outcomes will then be compared between the treatment groups. In particular, we will compare the two groups with regard to their efficacy in reducing corneal curvature. Secondary outcomes will include visual acuity. Safety assessments will include a tabulation of adverse events, patient symptoms, loss of visual acuity, changes in endothelial cell density, slit lamp examination of the cornea and lens, and contact lens tolerance for contact lens wearers

Inclusion Criteria:

• 18 years of age or older
• A diagnosis of keratoconus or a diagnosis of corneal ectasia after corneal refractive surgery
• Vision with contact lenses or glasses is worse than 20/20
• Corneal thickness greater than 375 microns at the thinnest point

Exclusion Criteria:

• Eyes classified as either normal, atypical normal, or keratoconus suspect on the severity grading scheme.
• Corneal pachymetry ≤ 350 microns at the thinnest point measured by Pentacam in the eye(s) to be treated.
• Previous ocular condition (other than refractive error) in the eye(s) to be treated that may predispose the eye for future complications
• Clinically significant corneal scarring in the CXL treatment zone
• Pregnancy (including plan to become pregnant) or lactation during the course of the study
• A known sensitivity to study medications
• Patients with nystagmus or any other condition that would prevent a steady gaze during the CXL treatment or other diagnostic tests.
• Patients with a current condition that, in the investigator's opinion, would interfere with or prolong epithelial healing.