The vitreous is attached to the retina, more strongly in some places than others. When a PVD starts the jelly comes away from the retina. The firm jelly-like substance of the vitreous changes with age. As it comes away from the retina it can cause the symptoms of posterior vitreous detachment. Many people are not aware that they have developed PVD but some notice symptoms such as floaters or flashing lights.
Floaters can take many forms from little dots, circles, lines, to clouds or cobwebs.
Sometimes people experience one large floater which can be distracting and make things difficult to read. As the outer part of the vitreous detaches from the retina it can pull on this light sensitive membrane, especially where the vitreous is attached quite strongly to the retina. The pull of the vitreous in these areas stimulates the retina. This stimulation causes the sensation of flashing lights since the brain interprets all stimulation signals from the retina as light. Unfortunately at the moment nothing can be done medically for this condition, usually people find that the symptoms calm down after about six months and people do eventually get used to living with the floaters.