The invention relates to non corrective unitary lens eyeglasses and safety helmets comprising a one piece shield as well as a method for designing and fabricating such a one piece shield. The method according to the invention for designing a one piece shield (300) for non corrective unitary lens eyeglasses or safety helmets whereby said shield (300) has a front surface (302) and a back surface (304) is computer implemented and comprises the following steps: providing a front surface geometry of said shield (300) providing a predetermined local relationship of said front surface geometry with respect to a predetermined center of rotation of at least one of a wearers eyes calculating a predetermined portion (307a 307b) of a back surface geometry of said shield (300) attributed to said at least one of said wearers eyes by establishing non zero minus power and minimizing prism as worn for a plurality of wearers lines of sight intersecting said back surface (304) within said predetermined portion (307a 307b) and said front surface (302) due to eye rotations of said at least one of said wearers eyes around said predetermined center of rotation of said at least one of said wearers eyes whereby said predetermined portion (307a 307b) of said back surface geometry is a freeform surface geometry.
