The technology provides for automatic alignment of a see-through near-eye, mixed reality device with an inter-pupillary distance (IPD). A determination is made as to whether a see-through, near-eye, mixed reality display device is aligned with an IPD of a user. If the display device is not aligned with the IPD, the display device is automatically adjusted. In some examples, the alignment determination is based on determinations of whether an optical axis of each display optical system positioned to be seen through by a respective eye is aligned with a pupil of the respective eye in accordance with an alignment criteria. The pupil alignment may be determined based on an arrangement of gaze detection elements for each display optical system including at least one sensor for capturing data of the respective eye and the captured data. The captured data may be image data, image and glint data, and glint data only.