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 the CXL procedure, the central corneal thickness has been shown to significantly change. The investigator's believe that better maintenance of corneal thickness potentially could have benefits of better reproducibility of the crosslinking effect with improved predictability of results.

The objective of this study is to investigate the difference between the two riboflavin preparations during UV (ultraviolet) administration. Both riboflavin preparations currently are in general use worldwide and in U.S. clinical trials of corneal collagen crosslinking. The first preparation contains riboflavin in a dextran solution, which may tend to dehydrate the cornea and keep it thinner. The second preparation contains riboflavin in a solution without dextran; in this case, the relative hypotonicity may tend to keep the cornea better hydrated and thicker. The primary goal of the study is to see if the use of hypotonic riboflavin (rather than riboflavin with dextran) better maintains consistent corneal thickness during the CXL procedure. The second goal of the study is to determine if better maintenance of corneal thickness potentially could have benefits of better consistency of the procedure, decrease in corneal haze formation, and improved safety of the endothelial cells. Safety and efficacy outcomes will then be compared between the groups. In particular, we will compare the corneal thickness measured by ultrasonic pachymetry immediately after the CXL procedure in the randomized eyes. Secondary outcomes will include visual acuity, longer term corneal thickness changes, and corneal steepness changes. 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 progressive keratoconus over a period of 24 months or less before randomization 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 300 microns at the thinnest point

Exclusion Criteria:

• Eyes classified as either normal, atypical normal, or keratoconus suspect on the severity grading scheme.
• Corneal pachymetry ≤ 300 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.