Floaters are deposits of various size, shape, consistency, refractive index, and motility within the eye's vitreous humour, which is normally transparent. They may be of embryonic origin or acquired due to degenerative changes of the vitreous humour or retina Floaters are visible because of the shadows they cast on the retina or their refraction of the light that passes through them, and can appear alone or together with several others in one's field of vision. They may appear as spots, threads, or fragments of cobwebs, which float slowly before the observer's eyes. Since these objects exist within the eye itself, they are not optical illusions but are entoptic phenomena.
Most spots are not harmful and rarely limit vision. But, spots can be indications of more serious problems, and you should see your optometrist or ophthalmologist for a comprehensive examination when you notice sudden changes or see increases in them.
By looking in your eyes with special instruments, your optometrist or ophthalmologist can examine the health of your eyes and determine if what you are seeing is harmless or the symptom of a more serious problem that requires treatment.