- This article refers to the entoptic phenomenon. See Floater (disambiguation) for other usages.
Floaters, or muscae volitantes (Latin: "flying flies"), are entoptic phenomena characterized by shadow-like shapes which appear singly or together with several others in one's field of vision. They can take the form of spots, threads, or fragments of cobwebs, that float slowly before one's eyes.
Floaters are suspended in the thick fluid of the eye. Thus, they generally follow the rapid motions of the eye, while drifting slowly within the fluid. Floaters located slightly to the side of one's direction of gaze can be particularly annoying. The temptation to try to look directly at them is almost irresistable. However, attempts to shift the gaze toward them are frustrated, because the floaters follow the motion of the eye, and remain to the side of the direction of gaze. On the other hand, because floaters are not perfectly fixed within the fluid, the brain does not get a chance to tune them out (as it does with the shadows of the eye's blood vessels, which are invisible under normal circumstances).
Floaters are particularly noticeable when lying on one's back and gazing at the sky. Despite the name "floaters," many of these specks have a tendency to sink toward the bottom of the eyeball, in whichever way the eyeball is oriented; the supine position tends to concentrate them near fovea, which is the center of gaze, while the textureless and evenly lit sky forms an ideal background against which to view them.
Floaters are not uncommon, although they rarely cause problems for those who have them. Floaters can be a nuisance and a distraction to those who suffer from severe cases, as the spots seem to drift through the field of vision. Ophthalmologists believe that the shapes are shadows projected onto the retina by tiny structures of protein or other cell debris discarded over the years and trapped in the vitreous humour. It is not, however, only elderly people who suffer from floaters; they can certainly become a problem to younger people, especially if they are shortsighted. They are also common after cataract operations or after trauma. In some cases, floaters are congenital.
If flashes do occur, however, or sudden "clouds" of minute spots move across the field of vision (as a whole), they must be investigated immediately as they may be symptoms of retinal tears or even a detached retina.
The cause of floaters is not understood. Some have associated their onset with mercury toxicity and liver function, among other things.
Normally, there is no treatment indicated. Vitrectomy operations to remove them are normally advised against as they are risky and may cause more severe problems or even blindness. One should bear in mind also that floaters may become less annoying as sufferers grow accustomed to them, to the extent even that they may no longer notice them.
An inquisitive person interested in a better view of his floaters may sharpen the blurry shadow image of many floaters significantly by reducing his pupil size, especially by looking through a pinhole at a bright surface. The head may be tilted in such a way that one of the floaters drifts towards the central axis of the eye. In the sharpened image the fibrous elements are more conspicuous. (If the pinhole is kept moving slowly in small circles, the same technique evokes an interesting entoptic effect known as the vascular figure , which is a view of the blood vessels within one's own eye).
Quotations
- A common experience... is for a person who has some ocular trouble that impairs his vision to become suddenly aware of the so-called mouches volantes in his visual field, although the causes of this phenomenon have been there in the vitreous humor all his life. Yet now he will be firmly persuaded that these corpuscles have developed as the result of his ocular ailment, although the truth simply is that, owing to his ailment, the patient has been paying more attention to visual phenomena.
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—H. von Helmholtz, Handbuch der Physiologischen Optik, published as "Helmholtz's Treatise on Physiological Optics, Translated from the Third German Edition," ed. James P. C. Southall, 1925, The Optical Society of America. v. III, pp. 6-7
- They could have done the same thing, alone, in the back yard, seeing the shapes swimming in the sky. I forget how old I was when I asked somebody about it, and I was told that those wonderful gliding changing spots were imperfections in the fluid of my eye-ball, that what I was seeing was in my eye. In your eye! For so long, for a child's years, the sky was full of wonder, these shapes were in the sky, the sky was full of transparent things that swooped and swam. They were almost invisible, and, I thought, almost bodiless, they were there, but you could go right through them, they were animals that lived in the air. You see, we didn't go around talking about things like this. It's only now, when I am grown up and know everything, that I talk about this.
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—Robert Paul Smith, 1957, Where Did You Go? Out. What Did You Do? Nothing. Norton, New York.
- At first the amoebae look like muscae volitantes, those curled moving spots you seem to see in your eyes when you stare at a distant wall. Then I see the amoebae as drops of water congealed, blusish, translucent, like chips of sky in the bowl.
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—Annie Dillard, 1974, "Pilgrim at Tinker Creek." Bantam: Toronto.
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Last updated: 08-23-2005 19:45:25
