A surgical system includes a light source, a sensor for detecting light, and a surgical device including an elongate shaft having a distal part positionable at a surgical working site within a body cavity. A first optical pathway transmits light from the light source to a distal part of the elongate shaft and onto tissue within the body cavity, and a second optical pathway receives light from tissue within the body cavity and transmits the received light to the sensor. A surgical drape, such as one covering a robotic manipulator arm housing components of the system, is positioned such that at least the first or second optical pathway includes an optically transmissive portion of the surgical drape.