See-through computer display systems

A head-worn display with folded optics for providing a displayed image overlaid onto a see-through view of a surrounding environment, comprising:

• a. a combiner that provides a see-through view of a surrounding environment and simultaneously redirects an image light toward a user's eye to provide the overlaid displayed image;
• b. a light source that illuminates the user's eye;
• c. a camera that captures images of the user's eye comprised of light reflected by the user's eye when the user views the displayed image overlaid onto the see-through view;
• and
• d. wherein the light source provides infrared light and the camera is sensitive to infrared light.