By far the commonest cause of floaters is a Posterior Vitreous Detachment or PVD. This typically causes the sudden onset of floaters and occasional flashing lights. A PVD is rare before the age of 40 and may be present in about 2 out of 3 seventy year olds. The vitreous jelly normally fills up the back four-fifths of the eye. With ageing, inflammation, surgery and short sightedness there is a tendency for the vitreous jelly to separate from the surface of the retina.

The posterior vitreous is usually glued to the surface of the retina at least at one point which is over the surface of the optic nerve head. When the vitreous detaches from the optic nerve head there is some naturally occurring glue left on the surface of the vitreous which is typically circular, oval or cobwebbed in shape. The glue is opaque and moves around causing a floating shadow. This is probably the commonest cause of floaters and is known as a Weis ring.

Pic : ( A )Detached and collapsed vitreous jelly has moved forward within the vitreous cavity. ( B ) Lens