Embodiments are described of an apparatus including an eyepiece having a front surface, a back surface spaced apart from the front surface, and an edge forming a perimeter of the eyepiece. The eyepiece includes an angled surface to direct light eye-measurement light reflected from an eye into the eyepiece and to direct display light out of the eyepiece to the eye. A first waveguide is formed in the eyepiece and extending from the angled surface to the edge, the first waveguide being optically coupled to a first portion of the angled surface having a first surface treatment. And a second waveguide is formed in the eyepiece and extending from the angled surface to the edge, the second waveguide being optically coupled to a second portion of the angled surface having a second surface treatment.