Floater

For other uses of "Floater", see Floater (disambiguation).

Image:Floater.jpg

Floaters, or muscae volitantes (Latin: "flying flies"), are entoptic phenomenacharacterized 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.

Description

Floaters are suspended in the vitreous humour, the thick fluid or gel that fills 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. When they are first noticed, the natural reaction is to attempt to look directly at them. 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. Floaters are, in fact, visible only because they do not remain perfectly fixed within the eye. Although the blood vessels of the eye also obstruct light, they are invisible under normal circumstances (and thus not annoying) because they are fixed in location relative to the retina, and the brain "tunes out" stabilized images (see neural adaptation). This does not occur with floaters and they remain visible, and, in some cases when large and numerous, annoying.

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. The shapes are shadows projected onto the retinaby tiny structures of proteinor 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 myopic. They are also common after cataractoperations or after trauma. In some cases, floaters are congenital.

Transparent floaters

There is, however, another common form of floater, often denied by opthalmologists, perhaps because they are too young to have experienced it first-hand. This seems to be the result of relatively transparent blobs of gelatinous body breaking free and drifting in the liquid part of the vitreous humour. Quite unlike the black spots and threads commonly observed by younger people, their main effect can be to suddenly defocus the image, and if they drift close to the lens they can badly defocus a whole column of print, or the view across a road, without apparently darkening it (perhaps because of differing refractive indices). They are easily distinguished from other causes of blurring by the fact that flicking the eyes to one side and back temporarily restores normal vision. It can be annoying for people with such floaters to be told that 'floaters are not a problem', though once understood they are easier to live with.^{[citation needed]}

Causes

There are various causes for the appearance of floaters, of which the most common are described here. Basically, any way by which material enters the vitreous humour is a cause for floaters.

Vitreous syneresis

The most common cause of floaters is shrinkage of the vitreous humour: this gel-like substance consists of 99% waterand 1% solid elements. The solid portion consists of a network of collagenand hyaluronic acid, with the latter retaining water molecules. Depolymerisationof this network makes the hyaluronic acid release its trapped water, thereby liquefying the gel. The collagen breaks down into fibrils, which ultimately are the floaters that plague the patient. Floaters caused in this way tend to be few in number and of a linear form.

Posterior vitreous detachments and retinal detachments

In time, the liquefied vitreous body loses support and its framework contracts. This leads to posterior vitreous detachment, in which the vitreous body is released from the sensory retina. During this detachment, the shrinking vitreous can stimulate the retina mechanically, causing the patient to see random flashes across his visual field. The ultimate release of the vitreous sometimes makes a large floater appear, usually in the shape of a ring. As a complication, part of the retina might be torn off by the departing vitreous body, in a process known as retinal detachment. This will often leak blood into the vitreous, which is seen by the patient as a sudden appearance of numerous small dots, moving across the whole field of vision. Retinal detachment requires immediate medical attention, as it can easily cause blindness. Both the appearance of flashes and the sudden onset of numerous small floaters warrant an ophthalmological investigation.

Regression of the hyaloid artery

The hyaloid artery, an artery running through the vitreous humour during the fetalstage of development, regresses in the third trimester of pregnancy. Its disintegration can sometimes leave cell matter.

Other common causes

Other causes for floaters include active toxoplasmosis, cystoid macular oedemaand asteroid hyalosis. The latter is an anomaly of the vitreous humour, where by calciumclumps attach themselves to the collagen network. The bodies that are formed in this way move slightly with eye movement, but then return to their fixed position.

Tear film debris

Sometimes the appearance of floaters has to be attributed to dark specks in the tear film of the eye. Technically, these are not floaters, but they do look the same from the viewpoint of the patient. People with blepharitisor a dysfunctional meibomian glandare especially prone to this cause, but ocular allergiesor even the wearing of contact lensescan cause the problem. To differentiate between material in the vitreous humour of the eye and debris in the tear film, one can look at the effect of blinking: debris in the tear film will move quickly with a blink, while floaters are largely unresponsive to it. Tear film debris is diagnosed by eliminating the possibility of true floaters and macular degeneration.

Treatment

Normally, there is no treatment indicated. Vitrectomyoperations 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.

Another treatment is laservitreolysis. In this procedure a YAG laseris focused onto the floater and in a quick burst vaporizes the structure into, presumably, a less dense and not as noticeable consistency. This procedure can be time consuming and there is no consensus as to how completely effective it is. One study found laser vitreolysis "to be a safe but only moderately effective primary treatment conferring clinical benefit in one third of patients" [1].

Observing floaters

Floaters are often readily observed by a doctor with the use of an ophthalmoscopeor slit lamp. Increasing background illumination or using a pinhole to effectively decrease pupil diameter may allow a person to obtain a better view of his or her own floaters. 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 effectknown 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 humour 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.

— 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.

— 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.

— Annie Dillard, 1974, "Pilgrim at Tinker Creek." Bantam: Toronto.

See also

• Blue field entoptic phenomenon, alias Scheerer's phenomenon- tiny bright dots moving quickly in the visual field.
• Phosphene

External links

• Floaters awareness
• My little page about big floaters
• The Eye and Floaters Information resource
• Floater Talk
• A German eye floaters portal site
• Floatersworld
• Eye Floaters Informations Centre
• Picture of the entoptic phenomenon: Vitreous Floaters(PDFfile, requires an AcrobatReader or plugin)
• The italian association on floaters(Italian-language)de:Mouches Volantes

it:Miodesopsie nl:Glasvochttroebeling ja:??? sv:Mouches volantes zh:???

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Floater Wikipedia article Floater.