An incision guide instrument for radial keratotomy has a lens positionable over a cornea, containing an incision guide slot adjacent to which is disposed two mirror surfaces within the lens. The mirrors are angled to allow a surgeon to observe and control the blade depth penetration into the cornea. The slotted, mirrored lens is rotatable and has clip and notch means to locate any of sixteen different radial incision positions. Transverse arcuate cuts are also allowed by the rotatable lens, and a stop means prevents the transverse cuts from contacting the radial cuts. An annular cone disposed over the sclera defines a vacuum chamber for holding the eye in position relative to the lens.