Floater

Floater Classification and external resources
Impression of floaters, as seen against a blue sky.
ICD-10	H43.9
ICD-9	379.24
DiseasesDB	31270
MedlinePlus	002085

Floaters are deposits of various size, shape, consistency, refractive index, and motility within the eye's vitreous humour, which is normally transparent.^[1][2] They may be of embryonic origin or acquired due to degenerative changes of the vitreous humour or retina.^[1] The perception of floaters is known as myodesopsia, or less commonly as myiodeopsia, myiodesopsia, or myodeopsia.^[1] Floaters appear as shadow-like shapes that 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 sufferer's eyes.^[2] Since these objects exist within the eye itself, they are not optical illusions but are entoptic phenomena.

One specific type of floater is either called Muscae volitantes (from the Latin, meaning 'flying flies'), or mouches volantes (from the French), and consist of small spots. These are present in most people's eyes and are attributed to minute remnants of embryonic structures in the vitreous humour.^[1]

Description

Floaters are suspended in the vitreous humour, the thick fluid or gel that fills the eye.^[3] Thus, they generally follow the rapid motions of the eye, while drifting slowly within the fluid. When they are first noticed, the natural reaction is to attempt to look directly at them. However, attempting to shift one's gaze toward them can be difficult since floaters follow the motion of the eye, remaining 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 because they are fixed in location relative to the retina, and the brain "tunes out" stabilized images due to neural adaptation. This stabilization is often interrupted by floaters, especially when they tend to remain visible.^[2]

Floaters are particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue 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 (looking up or lying back) tends to concentrate them near the fovea, which is the center of gaze, while the textureless and evenly lit sky forms an ideal background against which to view them.^[3] The brightness of the daytime sky also causes the eyes' pupils to contract, reducing the aperture, which makes floaters less blurry and easier to see.

Floaters are not uncommon, and do not cause serious problems for most people; they represent one of the most common presentations to hospital eye services. A survey of optometrists in 2002 suggested that an average of 14 patients per month per optometrist presented with symptoms of floaters in the UK alone.^[4] However, floaters are more than a nuisance and a distraction to those with severe cases, especially if the spots seem to constantly drift through the field of vision. 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. Floaters can even be seen when the eyes are closed on especially bright days, when sufficient light penetrates the eyelids to cast the shadows. 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 cataract operations or after trauma. In some cases, floaters are congenital.^[5]

Floaters are able to catch and refract light in ways that somewhat blur vision temporarily until the floater moves to a different area. Often they trick the sufferer into thinking they see something out of the corner of their eye that really is not there. Most sufferers, with time, learn to ignore their floaters. For people with severe floaters it is nearly impossible to completely ignore the large masses that constantly stay within almost direct view. Some sufferers have noted a decrease in ability to concentrate while reading, watching television, walking outdoors, and driving, especially when tired.^[5]

Causes

There are various causes for the appearance of floaters, of which the most common are described here. Simply stated, any damage to the eye that causes material to enter the vitreous humour can result in floaters.

Vitreous syneresis

The most common cause of floaters is shrinkage of the vitreous humour^[6]: this gel-like substance consists of 99% water and 1% solid elements. The solid portion consists of a network of collagen and hyaluronic acid, with the latter retaining water molecules. Depolymerization of 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 the visual field, sometimes referred to as "flashers." The ultimate release of the vitreous around the optic nerve head sometimes makes a large floater appear, usually in the shape of a ring ("Weiss ring").^[7] 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. Consequently, both the appearance of flashes and the sudden onset of numerous small floaters should be rapidly investigated by an ophthalmologist.^[8]

Regression of the hyaloid artery

The hyaloid artery, an artery running through the vitreous humour during the fetal stage of development, regresses in the third trimester of pregnancy. Its disintegration can sometimes leave cell matter.^[9]

Other common causes

Patients with retinal tears may experience floaters if red blood cells are released from leaky blood vessels, and those with a posterior uveitis or vitritis, as in toxoplasmosis, may experience multiple floaters and decreased vision due to the accumulation of white blood cells in the vitreous humour.^[10]

Other causes for floaters include cystoid macular edema and asteroid hyalosis. The latter is an anomaly of the vitreous humour, where by calcium clumps 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.^[8][3]

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 blepharitis or a dysfunctional meibomian gland are especially prone to this cause, but ocular allergies or even the wearing of contact lenses can 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.

Diagnosis

Floaters are often readily observed by a doctor with the use of an ophthalmoscope or slit lamp. However, if the floater is a small piece of debris and near the retina they may not be able to observe it even if it appears large to the sufferer.

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 effect known as the vascular figure, which is a view of the blood vessels within one's own eye.)^[11]

Treatment

Normally, there is no treatment indicated.

• Vitrectomy may be successful in treating more severe cases;^[12][13] however, the procedure is typically not warranted in those with lesser symptoms due to the potential for complications as severe as blindness. Floaters may become less annoying as sufferers grow accustomed to them, even to the extent that they may no longer notice them.^[14]

• There is also Sutureless Vitrectomy, as the standard vitrectomy involves cutting through the conjunctiva, or fleshy part of the front of the eye, and making openings in the pars plana area which require stitches at the end of the surgery. In the sutureless technique, small tubes or canulas or trochars are placed through the pars plana area and very tiny instruments are placed through these tubes. Once the surgery is complete, the tubes are removed and no stitches are needed. Only in certain cases can sutureless vitrectomy surgery be performed. ^[15]

• Another treatment is laser vitreolysis.^[16] In this procedure a powerful laser (usually an Yttrium aluminium garnet laser) is focused onto the floater and in a quick burst vaporizes the structure into a less dense and not as noticeable consistency.^[15]

References

See also

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

External links

• Eye-Floaters.com - Home of the Eye and Floaters Information Resource
• Eye-Floaters.com - Living With Floaters article
• Picture of the entoptic phenomenon: Vitreous Floaters (PDF file, requires an Acrobat Reader or plugin)
• Eye floaters - subjective vision simulator from Floatershell.com
• Floater Talk - Message board gathering many floater sufferers throughout the world
• Eye On Vision - To raise awareness/ campaign for research into for vitreous floaters and macular degeneration.