Abstract: A system for bilateral or monocular photochemical cross-linking of corneal collagen employs selectable light in a selected wavelength band as the excitation source and riboflavin as the photosensitizer. The system has an illumination source which may have multi-spectral capability, light guides for delivery of light to the optical head for projection onto the corneal surface, selectable radiation patterns to accommodate individual corneal architecture, and red light phototherapy to limit apoptosis and accelerate healing time. Aiming beams provide alignment of the optical head to the patient cornea. A microprocessor-controlled rotary solenoid mechanical shutter provides discontinuous illumination for tissue reoxygenation, and devices and methods may be included for the in situ determination of oxygen utilization and the riboflavin content of the cornea.