A retainer system is provided for tethering a cap to a body on an optic, where the cap and body define an inner cavity. The retainer system includes a lanyard and an inner attachment. The lanyard is fixed on a first end to a surface of the cap facing the inner cavity. The inner attachment is fixed on a first end to a second end of the lanyard and is fixed on a second end to an inside wall of the body facing the inner cavity. When the cap is closed on the body, the lanyard and inner attachment are contained completely within the inner cavity.