US Patent 7347551 Optical system for monitoring eye movement

A system for detecting eye closure through optical observation of the eye includes a frame configured to be worn on a user, a light source, and at least one eyepiece connected to the frame. The eyepiece has a reflective surface on a side facing the user's eye when the frame is positioned on the user and the reflective surface of the eyepiece is configured for reflecting light emitted from the light source onto the eye. A sensor is connected to the frame and is operable to detect light reflected by the eye in a direction that is substantially parallel to the light incident on a retina of the eye to detect that the eye is in an open position.