There may be some areas where the vitreous is very strongly attached to the retina. If the vitreous pulls away from the retina in an area where the retina is weak, the retina may tear. One condition that weakens the retina is called lattice degeneration. When lattice degeneration is present, it indicates that the retina is thin and may be more susceptible to a tear of the retina than in an area without lattice degeneration. Imagine a piece of scotch tape attached to tissue paper. If you try to pull the scotch tape off the tissue paper, you will tear the paper. A tear of the retina works very much the same way. If the vitreous is firmly attached, it can tear the retina as it pulls away. If the retina tears across a retinal blood vessel, there will be bleeding into the vitreous. This is called vitreous hemorrhage.
When there is a little bleeding, red blood cells floating and moving in the vitreous create the sensation of walking through a swarm of flies. If even more bleeding occurs in the vitreous, it looks like a spider web or a swirling mass of black or red lines. If there is a great deal of bleeding into the vitreous cavity, vision may be reduced significantly, or even become very dark. When a retinal tear occurs, it is a potentially serious problem. If a vitreous hemorrhage also occurs, it is even more serious.
The retina can tear immediately following a posterior vitreous detachment (PVD), or weeks later. If no tear has developed within eight weeks after a PVD, the retina probably will not tear.
Any patient, who experiences sudden or new floaters, or flashing lights of any kind, should have a complete retinal examination immediately. These symptoms may indicate that a retinal tear has occurred. A retinal tear may result in a retinal detachment. Since retinal tears and retinal detachments begin in the peripheral retina, your doctor may suggest that you test your peripheral vision to be sure there are no changes.