The eyeball is filled with a clear transparent semi solid gel like substance called the vitreous humour. It normally completely fills the eyeball and it sticks to the entire surface of the retina. However it undergoes liquefaction(becomes watery) and falls away from the retina and floats freely in the cavity of the eye, This process is called posterior vitreous detachment(PVD). This occurs naturally in normal people as a result of ageing and commonly occurs in middle aged people. It is also more common in shortsighted people and also after cataract surgery.
Floaters are the symptoms of this condition although other conditions like bleeding in the eye eg from diabetic retinopathy or inflammation can also cause floaters. The can take various forms and appear as dots, spots or lines or cobwebs. In the initial stages it is often associated with flashes of light which are sensation of streaks of light with movement of the eye. This can appear even in the dark as it is due to retinal stimulation from movement of the gel. The pulling of the gel can cause retinal bleeding or in more severe cases tears of the retina.
Floaters and flashes are important symptoms that need to be attended to. This is especially if they are new and of recent onset. The only way to exclude retina bleeding or tears is to have a full eye examination including a dilated retina check. Fortunately most people do not have any retina problems following the vitreous detachment and the floaters will then gradually subside. The symptoms will persist for weeks to months and in some people will continue be annoying. There is no specific medical treatment for vitreous floaters and surgery is not usually advised. Tears of the retina may be treated with laser to seal the tears and prevent retinal detachment from occurring.