This is a brief loss of vision, lasting for periods of seconds to minutes, usually caused by the temporary blockage of small blood vessels in the eye by tiny emboli (particles of clotted blood).
These emboli are carried in the bloodstream from diseased carotid arteries in the neck or, rarely, from the heart. Sufferers typically experience a loss or dimming of vision, in one eye only, rather like a shade being pulled down or up.
Attacks may be infrequent or may occur many times a day. This symptoms SHOULD never be ignored since it is a clear warning that the person has an increased risk of stroke or coronary heart disease.
Medical investigation, with special attention to the state of the arteries, is urgently needed.