The disclosure concerns altering the mechanical and/or chemical property of a body tissue, particularly an ocular tissue. In specific cases, it concerns altering or stabilizing the shape of the cornea, such as in a subject suffering or at risk for ectasia or keratoconus. In other specific cases, it concerns strengthening the sclera in a subject suffering or at risk for myopia. The invention employs light irradiation of a photoactivatable compound, such as one that applies crosslinking to the tissue, for example.