1. A head-worn computer, comprising: a. A camera adapted to capture a plurality of reflected images of a eye of a person wearing the head-worn computer to determine a plurality of positions of the eye, wherein the camera is positioned to capture the reflected images of the eye from an optical path that is in-line with an image-light path through delivery optics that are adapted to present an image to the eye; and b. A processor adapted to determine a rate of position change statistic describing a rate of positional change of the eye based on the plurality of reflected images, the processor further adapted to remove content from a field of view of a see-through display if the rate of positional change exceeds a predetermined threshold.