Eye floaters are caused by shadows from opacities suspended in the vitreous jelly that fills the eye.
The eye is filled with a clear jelly called vitreous. The vitreous jelly is composed of 98% water trapped within a matrix of collagen fibers. The collagen fibers are thin and regularly spaced, which allows light to pass through without interference.
Over time, the collagen fibers in the vitreous jelly start to condense, becoming thick and irregular. These collagen opacities cast shadows on the retina. The shadows drift in the vision as the vitreous jelly shifts with eye movement, causing floaters.
Sometime between the age of 50-70 in most individuals, the vitreous jelly spontaneously separates from the retina. This causes a sudden increase in collagen opacities within the vitreous jelly, along with a corresponding increase in floaters.
Although collagen opacities are the most common cause for floaters, any debris within the vitreous jelly can cast a shadow on the retina. Other potential sources of debris within the vitreous jelly include infections, inflammation, bleeding, and retinal tears.