Floaters
Floaters are dark spots that pass through your field of vision and move with your eye movements. Floaters often look like spots, lines, or cobwebs. Floaters are chunks of gel or cells that float inside the vitreous, the gel-like substance in the middle of the eyeball. Even though the floaters look like they are in front of the eye, they are actually inside of the vitreous. 
The images that you see are the shadows of the floating specs on the retina.
Injury may cause floaters, and sometimes pregnant women develop bits of protein in the eye that look like floaters. The vitreous in children is firm and gel-like. As we age, the vitreous becomes more and more water-like. During the transition between these two states, the gel may shrink and thicken, causing clumps to form on the inside of the eye. These are the clumps that cast shadows on the retina, causing floaters. As the vitreous changes consistency and shape, it may pull away from the back of the eye, causing a posterior vitreous detachment, which commonly causes floaters. Posterior vitreous detachments are more likely to occur in people who are nearsighted, have had cataract surgery, have had YAG laser surgery, and those who have had inflammation of the eye. It is important to see your retina specialist if you are seeing new floaters.
When the vitreous pulls away from the back wall of the eye, it is possible for a retinal tear to occur. A retinal tear can cause new floaters and a retinal detachment. Therefore, it is important that you see a retina specialist if you develop a new floater suddenly, or if you begin to see flashes of light. In most cases, floaters are not serious and fade on their own. However, floaters can be a warning sign of a more serious problem.