A touch screen arrangement fitted to a mobile telephone apparatus and built-on or resting on a substrate. The touch screen includes a display unit and a number of light pulse emitting units and a number of light pulse receiving units, said units being edge-related to said display unit. The light pulse emitting units and the light pulse receiving units are orientated adjacent said display unit, with the directions of said emitted and received light pulses being at right angles, or at least generally at right angles, to a planar surface on the display unit. The touch screen also includes four light pulse deflecting devices positioned close to the display surface.