A contact lens contains an inward pointing camera, which will be referred to as a retinal camera since it images light reflected from the retina. These can be reflections of physical features of the retina, of images of an external scene imaged by the eye onto the retina, or images projected onto the retina for example from small projectors contained in the contact lens (femtoprojectors). The field of view (FOV) of the retinal camera is sufficiently large that these reflections can be tracked relative to each other and/or relative to their position within the retinal camera's FOV. This information can be processed to track eye gaze and movement relative to the outside world, to align images from the femtoprojector with the eye and/or to align images from the femtoprojector with images from the outside world, among other tasks.
