Optical fibres enable doctors to look at the internal spaces, primarily the lungs and stomach, without surgery. The device used to do this is called an endoscope, and consists of a bundle of fibres inserted into a persons mouth, down their throat and into their lungs or stomach. Light is sent down the fibre bundle to provide illumination. Light is reflected from the surface of the stomach or lung and an image can be made.
If an ulcer is found in the stomach, a laser beam can be sent down the fibres to seal the ulcer. If cancer is suspected in the lungs, further investigations can be made. A sample can be taken and sent for analysis.