Particles that appear to be floating in a person's field of vision. They move quickly as the eye moves, but when the eye is still they seem to drift. Vision is not usually affected. Most floaters are shadows on the retina from minute particles in the vitreous humour (see EYE) which lies in the main part of the eyeball behind the lens. As a person ages, the jelly-like vitreous humour usually shrinks a little and becomes detached from the retina; this produces floaters which vanish over time. If a person notices a sudden cloud of floaters, sometimes accompanied by flashes of light, it is likely that a tear in or detachment of the retina has occurred. This requires prompt medical attention (see EYE, DISORDERS OF – Retinal detachment).