The inside of the back of the eye is filled with a gel known as the vitreous. It is usually loosely attached to the retina at the back of the eye and very firmly attached around the inside towards the front. A posterior vitreous detachment occurs when the outer wall of the vitreous gel bag separates at the back from the inner wall of the retina. This process is analogous to the bladder inside a football deflating. Individuals who develop a posterior vitreous detachment are typically aware of a sudden onset or change in their floaters and will often experience flashing lights or arcs of light, particularly in the dark. A posterior vitreous detachment not only causes visual symptoms but can also lead to a retinal tear and, subsequently, in an important minority of cases, a retinal detachment. The development or evolution of vitreous detachment also underlies many of the conditions managed by vitreoretinal surgeons, such as epiretinal membranes and macular holes.
Individuals who develop a sudden change in floaters or flashes are recommended to have a retinal examination ideally within the next 48 hours. If a curtain or shadow appears in part of their then more urgent attention is required as this suggests that a retinal detachment may have occurred.