Interpupillary distance measuring device with no moving parts

Claim 1

Device for measuring the interpupillary distance of a person, for example to assist with fitting eyeglass frames, comprising a box; a generally flat front panel of said box adapted to be applied to the face of a person in a known relative position so that a main axis normal to said front panel and a horizon plane containing said main axis respectively pass equidistantly between and through the centers of the eyes of said person which are at a fixed distance from said front panel; windows in said front panel adapted to be aligned with the eyes of said person; a convergent master lens in said box near said front panel with its optical axis coincident with said main axis; a point light source optically on said main axis at a position such that it determines for said person viewing it through said master lens a determined observation distance, light emitted by said point source forming respective corneal reflections on the corneas of said person; a measuring scale in said horizon plane normal to said main axis, optical images of said corneal reflections coinciding with respective divisions on said scale; means for identifying said respective divisions; means for calculating and displaying an interpupillary distance corresponding to an identified pair of divisions; an objective lens adapted to form in an image plane containing said scale a pair of real images of said corneal reflections viewed through said master lens; at least one photo-electric device in said scale comprising an array of sensitive members constituting scale divisions; and means for sequentially scanning said array to determine the rank therein of the members at which said positive images of said corneal reflections are formed.