Floaters are caused when the vitreous gel behind your eyeball liquefys, and small clumps are left behind. What you are actually seeing is the shadow they cast on the retina. The other type of floaters is caused when blood cells enter the vitreous gel, usually from people suffering of postular hypotension (get dizzy after changing position quickly due to low blood pressure)
Are they harmful?
No. Most people get them, usually middle-aged people, but it's nothing to worry about. If your floaters obscure your vision such that you have difficulty reading, then laser treatment is possible.
Eye floaters due to blood cells typically dissappear, but I'm not sure after how long. I've had them for about 4 weeks now, still no improvement. Any doctors here?