Endoscopy, a technique used to explore the stomach or other inner parts of the body is based on the phenomenon of

Modern flexible endoscopes use optical fibers to transmit light into the body cavity and transmit the image back out. Light travels along these fibers by repeatedly undergoing total internal reflection at the interface between the fiber core and its cladding. When light strikes the interface at an angle greater than the critical angle, it is reflected back into the core, allowing it to be guided along the curved path of the fiber.