Spots Before Your Eyes?
You have probably seen them—little gray flecks just out of focus that appear to float before your eyes. You may notice them when you’re reading or when you look at a light-colored wall or a cloudless sky.
IF YOU have ever tried to focus on one of these flecks, you know you can’t. The smallest movement of your eyes sends them racing off, and even if one slides down into your line of sight, you still can’t figure out what it is.
What are these flecks? Are they on the surface of your eyeball, or are they inside? Blink your eyelids without moving your eyes. If the spots change motion or disappear, they’re on the surface and are not the subject of this article.
But if there is little or no change, then they are inside, suspended in the vitreous humor, the fluid that fills the inner chamber of your eyeball. Since they are behind the eye’s lens, they remain blurry. And since the vitreous humor is a jelly not much thicker than water, they can drift, dancing away when you try to see one directly. It is from this that they get their medical name—muscae volitantes, meaning “flying flies.”
Where Do They Come From?
Just where do these spots come from? Some are leftovers from processes that took place before you were born. Early in a baby’s development, the interior of the eye is quite fibrous. By the time of birth, these fibers and other cells have changed to become the vitreous humor. Some cells and bits of fiber may remain, however, and these are free to float. There is also a canal from the optic nerve to the lens that in the unborn carries an artery to the lens to nourish it. The artery atrophies and is absorbed, usually before birth, but tiny portions of it may remain.
But there are other sources. Even in an adult, the vitreous humor is not all gel. It is enclosed by the delicate hyaloid membrane. This is pressed against the retina, the screen of light-sensitive tissue that lines most of the inside of your eye and that captures what you see. The hyaloid membrane attaches to the retina all around its front edge. From this seam tiny fibrils radiate throughout the vitreous humor.
As we get older, these fibrils begin to shrink. This causes some of them to break off. The vitreous humor also becomes more liquid, so broken pieces of fiber can float in it more freely. The vitreous humor itself also shrinks ever so slightly and begins to pull away from the retina, possibly leaving other cellular debris in its wake. Thus, with age you will see more of these “flying flies” drifting and swirling about in your field of vision.
Another source of small floaters can be the blood vessels of the retina. A blow to the head or any excessive pressure on the eyeball can cause a small vessel to release a string of red blood cells. Red cells are sticky, so they tend to cluster or to form a chain. Single cells or clusters may migrate into the vitreous humor, and if they remain near the retina, they may be visible. Red cells can be reabsorbed by the body, so eventually they disappear. These are not technically muscae volitantes, however, since they are the result of minor injury.
Does the presence of muscae volitantes indicate that something is wrong? Generally not. People with normal eyes, even young people, see them, and gradually they learn to ignore them. But certain conditions can indicate danger.
When Danger Threatens
If you suddenly notice many more specks than before, this may mean that something abnormal is happening. Especially is this true if you also see little flashes of light from inside your eyes. These phenomena come from the retina, where light is converted to nerve impulses. The shower of floaters and the light flashes are usually due to some detachment of the retina. How does this happen?
The retina has the consistency and thickness of a piece of damp tissue paper and is just about as delicate. Its light-sensitive layer is anchored to the layer behind it and to the vitreous humor only at its front margin and at the optic nerve, with a weaker attachment at the focal center. The vitreous body helps hold the rest of the retina in place. The eye is so resilient that even blows do not usually cause the retina to rip or to separate from its bed.
A blow can, however, cause damage that weakens the retina in a certain area or causes a tiny tear or hole. Such a hole can also come from an adhesion between the vitreous humor and the retina: A sudden movement or injury makes the vitreous humor tug on the retina, resulting in a small tear. Fluid from the vitreous chamber can then leak in behind the retina, lifting it from its bed. This disturbance causes the light-sensitive nerve cells to fire, and these are perceived as flashes.
Hemorrhages, small or great, sometimes accompany the separation, for the inner surface of the retina has its own network of blood vessels. Blood cells escape into the vitreous humor, and these are seen as a sudden flurry of floaters. Shortly after this, as the retina detaches, a veil, or curtain, of blindness cuts into the field of vision.
Hence, if you ever notice an upsurge in the number of flecks, especially when accompanied by flashes, go to an ophthalmologist or to a hospital at once! It could be a retinal detachment. Corrective measures may be impossible after the retina detaches extensively.
Have you seen spots before your eyes for years but without light flashes? There is probably no need to worry. Almost everyone else sees these spots too. If you ignore them, they won’t go away, but the brain learns to suppress the images as you go about your daily activities. The fact that they can exist without any real detriment to vision is testimony to the resilient design of the eye and the adaptability of the brain.
However, before they can say with certainty that there is no need to worry, people with floaters should be examined by an ophthalmologist or optometrist.
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Origin of Modern Refractive Correction
If you wear prescription glasses or contact lenses, in a sense you have muscae volitantes to thank. It was curiosity about these that led Frans Cornelis Donders, an eminent 19th-century Dutch physician, to begin scientific investigation of the physiology and pathology of the eye. In addition to identifying some of the sources of muscae volitantes, he discovered that farsightedness is due to a shortening of the eyeball and that the blurred vision of astigmatism is caused by uneven surfaces of the cornea and lens. His studies made possible the development of prescription eyeglasses.
Courtesy National Library of Medicine
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Tear in retina
Optic nerve leading to brain