A transmissive element including a diffractive and/or refractive pattern can be used with a display screen of a computing device to allow the display screen to function as a near field optical sensor (NFOS). The NFOS can be used to detect shadows cast on the display screen, and/or bright objects detected near the display screen, which can be used to determine the relative position of one or more features with respect to the device. These features can be, for example, the fingers or thumbs of a user attempting to provide input to the computing device. The device can support motion or gesture detection using cameras of the device, and touch input using touch screen functionality, but the NFOS can enable the device to also track motion in the dead zone between the field of view of the cameras and the touch screen.