The retina lies in the back of the eye and is a multi-layered tissue which detects visual images and transmits these to the brain. In front of the retina lies the vitreous humor. The vitreous is the jelly-like material that fills the large central cavity of the eye. It is composed primarily of water, but it is also made up of proteins and other substances which are more fibrous. The water and fibrous elements together give the vitreous the consistency of gelatin.

The vitreous is normally connected to the retina. During aging, the watery portion of the vitreous separates from the fibrous portions. As this occurs, the fibrous elements contract and can pull the vitreous away from the retina. This is called a Posterior Vitreous Detachment. This contraction on the retina is responsible for the characteristic "flashes" that often accompany the Posterior Vitreous Detachment. The "floaters" are frequently caused by the fibrous elements changing position during the Posterior Vitreous Detachment. They can also be caused by pieces of the retina being dislodged as the vitreous contracts. Besides aging, flashes and floaters are also associated with nearsightedness and injuries to the eye.

All patients who experience a recent onset of flashes and floaters should be examined immediately by their eye doctor. Most of the time nothing unusual is found, and simple reassurance is all that is needed. The flashes eventually go away, and the floaters diminish and become less bothersome with time.

However, in about 10% of the patients with a Posterior Vitreous Detachment, a tear of the retina is found. If left untreated, these tears may lead to a full retinal detachment. A full retinal detachment is a very serious sight threatening condition requiring a major surgical procedure to repair. When symptoms appear, it is important to examine the eye within a day of their onset. Changes can occur rapidly, and time can be of the essence if a retinal detachment is present.

Retinal tears are treated by sealing the tear with a laser or freezing technique (cryotherapy).