A pair of eyewear has transparent waveguides in each eyewear lens. An illumination subsystem directs a beam of light through the waveguides onto a wearers eyes. A First Purkinje point imaging subsystem for each lens uses light reflected from the eyes through the waveguides. A controller calculates from the positions of the First Purkinje points the wearers gaze parallax angle and/or the distance to an object of interest on which the gaze of the wearers eyes converges. The output of the controller may drive variable-focus eyeglass lenses to enable a presbyopic wearer to focus on the object. Modified Alvarez variable-focus lenses are described.
