LetinAR patent (bold by me):
Furthermore, the conventional devices have a limitation in that a virtual image becomes out of focus when a user changes focal length when gazing at the real world. To overcome this problem, there have been proposed technologies such as a technology using a configuration such as a prism capable of adjusting focal length for a virtual image and a technology for electrically controlling a variable focal lens in response to a change in focal length. However, these technologies also have a problem in that a user needs to perform a separate operation in order to adjust focal length or in that hardware such as a separate processor for controlling focal length and software are required.
In order to overcome the above-described problems of the conventional technologies, the present applicant has developed a device capable of implementing augmented reality by projecting a virtual image onto the retina through the pupil using a reflective unit having a size smaller than that of a human pupil, as described in patent document 1.