Floaters are small, semitransparent particles which appear in front of your vision. They exist in different shapes, sizes, numbers and forms. They may look like spots, threadlike strands or cobwebs. Floaters will move as your eyes move and seem to dart away when you try to look at them directly. They may not be always visible but may be more noticeable under white or bright backgrounds.
Floaters are actually located inside the vitreous, which is a jelly-like fluid filling the eyeball to maintain its shape. Floaters are usually small protein flecks which were trapped during the formation of the eyes before birth. The deterioration of the vitreous due to injury, disease or ageing could also cause these specks to become mobile inside the eyeball. When these particles move following your eyeball rotation, their shadow casts on your retina and form the appearance of floaters.
Although floaters itself may not affect vision, sometimes they can indicate severe sight-threatening conditions such as retinal tear and detachment. Optometrists can perform dilated fundus examination to rule out severe causes of floaters. It should be done every year to monitor any retinal changes. If you have had previous head or eye injuries and experience a sudden increase in floaters, especially in either eye and usually after flashes, you should immediately consult your eye care practitioner for a diagnosis.
Reference: American Optometric Association. American Academy of Ophthalmology.