We have developed a system called Borehole Optical Stratigraphy which can detect annual layers in boreholes in polar firn. Borehole Optical Stratigraphy consists of a downhole camera package and post-processing routines, which allow us to measure the intensity of light emitted from an on-board source and returned from the borehole wall. We manually identify the annual layers in this optical signal. We used this system at Siple Dome, Antarctica, in the 2001--2002 austral summer season. Our results agree well with counts of annual layers detected with two different methods in an ice core recovered 50 meters from our borehole.