Apparatus for guiding surgical formation of a pair of symmetrical sclerectomies in an eye of a patient, including a multi-diameter generally circular cutout portion including at least a first and second portions having corresponding first and second diameters, the cutout portion being arranged for placement over the limbus of the eye and for centering the limbus within one of the first and second portions, thereby enabling estimating the diameter of the limbus, and at least first and second series of sclerectomy guiding apertures formed about the cutout portion, each guiding aperture of the first series having a paired guiding aperture in the second series formed 180° thereapart relative to a center of the cutout portion, the at least first and second series of sclerectomy guiding apertures together including at least one pair of guiding apertures having a diameter therebetween which is wider than at least one of the first and second portions.