Everybody has a jelly called the vitreous inside the eye. The vitreous is located behind the coloured iris and normally rests against the retina. In a vitreous detachment the vitreous shifts forward and comes away from the retina; because it is the back of the vitreous that is affected the condition is also known as a posterior vitreous detachment.
A posterior vitreous detachment is very common, and affects most people some time in middle-age.
The vitreous is a firm jelly when we are young, but in time becomes more watery. The vitreous is encased within a bag, and if a small break forms in this bag the fluid from the vitreous can seep through the break and force the back of the vitreous away from the retina.
As the vitreous becomes progressively more fluid its scaffolding is prone to collapse and clump together. These thickenings within the vitreous cast a shadow on the retina and are seen as floating shapes in the vision. These floaters are more noticeable when looking at a pale wall or on a sunny day owing to the more stark contrast.
During a posterior vitreous detachment the number of floaters greatly increases. These may also be accompanied by flashes of light caused by the vitreous tugging on the retina as it detaches.
These flashes are often crescent shaped.
A posterior vitreous detachment does not normally cause any harm to the eye. The vitreous typically takes about two weeks to fully detach and after this time flashes are uncommon. The floaters may persist longer, and sometimes do not go away completely. However, with time floaters may break-up and sink downwards with gravity away from the line of sight and so typically become less noticeable.
More rarely, the movement of the vitreous away from the retina results in traction that tears the retina. Fluid moving through the retinal break may float the retina off the back of the eye leading to a retinal detachment. A retinal detachment is a serious complication because if it is not reattached soon it leads to permanent loss of sight. It is for this reason that you should contact an eye specialist immediately if you develop new floaters, flashes or persistent black shadows at the edge of your vision.
A posterior vitreous detachment is diagnosed following an examination with a slitlamp biomicroscope and an inspection of the retina following the use of eyedrops that dilate the pupil.
An isolated posterior vitreous detachment is harmless and does not require treatment. In the rare cases where it is accompanied by a retinal detachment surgery is required to prevent visual loss.