Sometimes we get little bits of debris floating around in the liquid (called the "vitreous humor") that fills our eyes. This can include blood cells (round) or fungal filaments (which look like a thick thread with small lines along it). Oddly, the lens in our eye then acts like a microscope, allowing us to see them floating around in our eyes.
These are very common, and when they have come on gradually (over months to years) and there are just a few of them, they are normal and not dangerous. When there is a new sudden shower of them in one eye, this can represent a medical emergency (called a "retinal tear") which should be seen immediately. A simple laser technique can fix the tear if done early, where vision may not be recovered if the tear is allowed to progress.
As noted in the Background discussion, unless the "floaters" are suddenly occurring in 1 eye, and there are suddenly a lot of them, they can generally be ignored. Interestingly, the longer thread like floaters (vs. the small round ones) sometimes reflect an overgrowth of yeast (Candida ) in the body, and go away when the yeast is addressed for 6 weeks with the prescription Diflucan 200 mg a day (see "Candida/Yeast Overgrowth"). If you have fatigue, pain, sinus congestion or spastic colon, these thread-like floaters may reflect yeast overgrowth, and addressing the yeast can help you feel better in general!
Jacob Teitelbaum, M.D. is one of the world's leading integrative medical authorities on fibromyalgia and chronic fatigue. He is the lead author of eight research studies on their effective treatments, and has published numerous health & wellness books, including the bestseller on fibromyalgia From Fatigued to Fantastic! and The Fatigue and Fibromyalgia Solution. Dr. Teitelbaum is one of the most frequently quoted fibromyalgia experts in the world and appears often as a guest on news and talk shows nationwide including Good Morning America, The Dr. Oz Show, Oprah & Friends, CNN, and Fox News Health.