If one has many floaters or flashing lights we worry about a retinal tear or detachment.
When the vitreous jelly collapses (See Posterior Vitreous Detachment) it peels off the wallpaper at the back of the eye which is the retina. The retina is what allows one to see. When the vitreous jelly peels off the retina, a break or a tear in the retina can occur. When a tear is present, the fluid inside the eye can go under the tear and cause the wallpaper to peel off. This is a retinal detachment.
If a patient is seen when there is only a tear, then laser or a freezing technique termed cryopexy can be done to spot weld the tear to prevent it from progressing to a full blown retinal detachment.