An input device comprising an overlay for a display screen comprising an optically conductive material is described. The overlay has a central region for transmitting first electromagnetic radiation corresponding to an object in contact with the overlay at a first location, and a light conduit along the edge of the central region for receiving and transmitting the first electromagnetic radiation. The light conduit is configured to inhibit transmission of the first electromagnetic radiation back into the central region of the overlay. At least one detector is coupled to the light conduit for receiving the first electromagnetic radiation and generating a signal indicative thereof. Location circuitry receives the signal and generates location data indicative of the first location.