Floater

Definition
noun, plural: floaters
(ophthalmology) One or more spots or threadlike specks that seem to float or move in one’s visual field caused by a shadow cast on the retina by vitreous debris; muscae volitantes
(general) One that floats
Supplement
A floater, in general, pertains to the one that floats. In ophthalmology, a floater refers to the one or more spots or threadlike specks in the visual field. These floaters in front of one’s vision seem to move and float (thus, the name). These floaters are due to the shadow cast on the retina by vitreous debris. The vitreous humor is the clear fluid within the eyeball. It fills the chamber between the lens and the retina. It is gel-like and comprised of water, salts, sugars, vitrosin, and proteins. Cells may also be present in the vitreous humor. Phagocytes are one of them. Phagocytes are immune cells capable of phagocytosis. They “eat up” cellular debris to clear the visual field. Another group of cells is the hyalocytes, which produce hyaluronic acid and collagen.
The vitreous humor is transparent when young. However, flaws gradually develop as one ages. The gel in the vitreous humor is not replenished continuously and as such becomes stagnant. Consequently, cells and other substances could be deposited in it as floaters. The perception of these floaters is referred to as myodesopsia. These floaters that look like floating spots or threads in the visual field are caused by the shadows casted by vitreous debris.
See also:

• Vitreous humor