Flashes and Floaters
Floaters are small dark spots, hair-like strands or cob-web type opacities which appear to float in front of the vision. They are especially noticeable when looking at a bright uniform background eg white wall or cloudless blue sky. They move with eye movements, often darting away if you try to look at them directly. They tend to occur with age and are due to changes in the vitreous jelly inside the eye.
In children and young adults the vitreous gel is fairly solid (like "party" jelly) but it tends to become more watery and mobile with age. This occurs earlier in short-sighted (myopic) people or in people who suffer direct trauma to the eye. Eventually the vitreous gel breaks away from the retina ("image capturing tissue") lining the back of the eye and collapses into the centre of the globe.
The vitreous gel is coloured mauve in this illustration and fills up most of the space inside the eye
As the vitreous gel detaches it can pull on the retinal tissue causing flashes of lights (photopsia) to be seen. These are subjective lights eg like a street lamp flickering, but there is no true objective stimulus. The apparent lights are usually seen in the peripheral side vision, especially noticeable in darkness. This is pulling of the vitreous gel on the retina is known as vitreo-retinal traction and may continue for several weeks. Eventually the traction is released and the vitreous gel completely detaches from the retina = posterior vitreous detachment (PVD). A posterior vitreous detachment is present in over 60% of people over the age of 70 years.
More rarely floaters can be caused by other eye conditions eg: inflammation (vitritis), vitreous haemorrhage, retinal infections. Flashes can also occur in other situations, unrelated to vitreous traction eg: migraine.
Retinal Tears/Detachment
In the vast majority of people with flashes and floaters, the vitreous loosens and detaches without causing any damage to the retina. However in a small number of cases the vitreous gel pulls a tear in the retina. If detected early retinal tears can usually be effectively "sealed off" using laser treatment, but undetected tears can result in the retina peeling away from the back of the eye = retinal detachment. This is a serious sight threatening condition which requires urgent specialised surgery to reattach the retina.
Retinal detachment left eye. The retina between 1 and 3 o clock is pale and "ballooning" forwards as it peels away from the back of the eye.
It is impossible to predict who may develop retinal tears/detachment and therefore anyone who develops new floaters +/- flashes should seen fairly urgently to have a thorough vitreous and retinal examination through dilated pupils.