case being a positive meniscus crescent in shape in the present invention this correction is readily surgically placed permanently into the patient 39 s cornea 51 this prescription is converted mathematically to the optical equivalent 43 seen in fig4 having planar 44 and convex 45 sides which as seen in fig5 is then ground 46 into the flat face 47 of the insert 48 of the present invention which as described below fits into the cutting instrument 110 as seen in fig7 and as explained below in connection with fig2 28 the optically ground concave correction portion 46 of flat face 47 of the insert 48 will in the present invention after proper adjustment of the vacuum be the only portion of the face 47 to come into direct contact with the cornea 51 at the time the cut is made the instrument 140 is affixed to the sclera 52 of the eye 50 by a suction ring 71 fig2 on the line 53 fig7 with a partial vacuum applied as seen schematically in fig7 when the partial vacuum is applied to the sclera 52 and adjusted to the proper level a downward force is applied to cornea 51 raising the innerocular pressure in.