Floaters & Flashes
Floaters are little black specks, cobwebs or strands that float about in the field of vision. They move as the eyes move and seem to dart away when you try to look at them directly. They are often visible when looking at a plain background, like a blank wall or blue sky.
Floaters are tiny clumps of cells or material inside the vitreous, the clear, gel-like fluid that fills the inside of your eye. They occur when the vitreous shrinks. As the vitreous shrinks it separates up a bit and becomes somewhat 'stringy'. The strands cast tiny shadows on the retina, which is what you see.
Floaters can be distracting at first but eventually they settle below the line of sight, but they do not go away completely. Most people learn to ignore them.
In most cases vitreous shrinkage and floaters are part of the natural ageing process and are harmless. Occasionally, however, an increase in floaters can be a sign of problems, especially if they are accompanied by lots of flashing lights.
Flashing lights is a common symptom experienced by many people. Common causes include migraines or from vitreous detachment, which is shrinkage of the jelly inside the eye.
With age the vitreous gel starts to liquify and collapse, pulling away from the retina, that it is usually attached to. When it pulls on the retina it creates a series of electrical impulses that are interpreted by the brain as flashes.
Most of the time the pulling on the retina causes no damage, however occasionally it can tear the retina. If left untreated a tear can allow fluid from within the eyeball to seep under the retina, causing it to separate and detach.
For this reason it is important that if you experience persistent flossing lights, particularly if accompanied by a sudden onset of floaters, that you have your eyes checked immediately to check for a retinal tear or detachment. If a tear is found it can be lasered down to seal it.
Excellent information on flashes and floaters is available from the American Academy of Opthalmology website here