A disposable fiber optic sheath assembly for illuminating a region within a mammalian body comprising a tubular sheath (204) having an outer surface with a diameter of less than 3 mm and a concentric array of optical fibers (216) within the outer surface, the optical fibers (216) having a packing factor within the concentric array of at least 80%, an optically transparent element (560) sealed at the distal end of the sheath(204) and a connector assembly (512) at a proximal end of the sheath.
