Devices and approaches for activating cross-linking within at least one eye component of an eye to stabilize and strengthen corneal tissue or other tissues of the eye. Cross-linking is activated within the at least one eye component by conveying a cross-linking agent to regions of the at least one eye component and then activating the cross-linking agent by delivering an initiating element to the at least one eye component. Approaches disclosed herein allow for precisely controlling the three dimensional region of strengthened tissue by conveying the cross-linking agent to regions of the at least one eye component. Approaches allow for conveying the cross-linking agent to a depth below the corneal surface such that cross-linking is activated below the corneal surface.