A laser beam guidance system comprises a combination of mirrors that establishes an optical channel within which the laser beam (22) is confined for movement. The system also includes means for moving the combination of mirrors to spatially reorient the optical channel. A beam steering scanner located on the path of the laser beam moves the beam within the optical channel onto selected paths which generally follow the longitudinal axis of the channel. Additionally, a focusing element (26) in the system brings the beam into focus at selectable points on the beam. In accordance with a pre-established program, the beam is moved within the channel and focused at points along the beam to photochemically affect cells in the cornea of the eye.