Mach bands or the Mach effect refers to an optical phenomenon from edge enhancement due to lateral inhibition of the retina . This is an inbuilt edge enhancement mechanism of the retina, where the edges of darker objects next to lighter objects will appear lighter and vice versa, creating a false shadow .
This has been attributed as a source of diagnostic error in radiology:
- a dark halo around a dense breast lesion in mammography
- apparent pneumomediastinum - the so-called pseudopneumomediastinum
- mimic a fracture
- pseudopneumothorax secondary to skin fold
Knowledge of the phenomenon may help prevent Mach bands being mistaken for a true abnormality such as pneumomediastinum.
History and etymology
Named after the Austrian physicist Ernst Waldfried Josef Wenzel Mach (1838-1916) who first described it in 1865 .