How do endoscopes use optical fibres to form images inside the body?

Endoscopes utilize fibre-optic technology to visualize internal body structures by employing bundles of thin, transparent glass or plastic fibers. These instruments typically use two distinct bundles: one to illuminate the target area and another to transmit the image back to the observer or a camera.1

The fundamental physical principle enabling this is total internal reflection. Each fiber consists of a core with a high refractive index surrounded by a cladding of lower-index material. Light entering the fiber core reflects repeatedly off the interface between the core and the cladding, allowing it to travel along the fiber—even when the instrument is bent or twisted—with minimal loss of intensity.123

To form an image, an ordered bundle of these fibers acts as an elongated lens. The image projected onto one end of the bundle is effectively dissected, transmitted through the individual fibers via successive internal reflections, and reconstructed at the opposite end for examination. Because the fibers are arranged in a precise, consistent order at both ends, the device can accurately reproduce the image of the tissue being examined.23