An optical fibre is a transparent thin fibre, usually made of glass or plastic for transmitting light Optical fibres are used in imaging optics, and work on the principle of total internal reflection of light. Bundles of fibres are used along with lenses for long, thin imaging devices called endoscopes, which are used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures (endoscopy).