The vitreous is a jelly like substance that makes up a substantial portion of the back of the eye, separating the major components at the front of the eye from those at the back ( the retina).
As the eye ages the vitrous can shrink and become detached from the retina. This is called a PVD or posterior vitreous detachment. Approximately 75% of people over the age of 65 will have a PVD.
Apart from an initial increase in the number of floaters and flashes, the condition is harmless. Symptoms usually subside after a while as the brain gets used to them.
Occasionally however it can develop into a retinal tear which is more serious. If vision suddenly deteriorates or you have a sudden increase in the number of floaters of notice the appearence of a dark curtain or cobweb in the feild of vision, seek the immediate attention of an ophthalmologist