Black floaters in the field of vision can mean age-related changes in the eye, a detached retina or bleeding in the eye, according to Mayo Clinic. Another cause is inflammation in the back of the eye, or posterior uveitis.
When floaters are age-related, it is because of changes in the vitreous humor, a jelly-like material that gives the eyeball its shape, states Mayo Clinic. As a person ages, the vitreous humor in the eye starts to liquefy and pull away from the inside of the eyeball. This causes the vitreous humor to clump up and turn stringy. What the person sees as floaters in the field of vision are the shadows of these clumps and strings. If the vitreous humor pulls away from the inner eye with enough force, it can tear the retina and cause it to detach. This leads to fluid build-up and black floaters behind the retina. If this condition isn't remedied, it can lead to loss of vision or blindness.
Bleeding into the vitreous humor also causes black floaters, as Mayo Clinic explains. The bleeding can have several causes. Posterior uveitis happens when the layers of the uvea become inflamed. The uvea is a structure found behind the white of the eye, and it helps the eye adjust to different light levels or the distances of objects, explains MedlinePlus.