You've probably seen them: small, diffuse gray spots that appear to float before your eyes. You can notice them when reading or looking at a light wall or a cloudless sky.
If you've tried to focus on any of these reasons, you know you can't. The slightest movement of your eyes will cause them to run, and even if one of them slips into your line of sight, you still can't figure out what it is.
What are these points? Are they on the surface of your eyeball or inside? Blink your eyelids without moving your eyes. If the spots change or disappear in motion, they are on the surface and are beyond the scope of this article.
But when there is little or no change, then they are inside, hanging in the vitreous humor, the fluid that fills the inner chamber of your eyeball. Because they are behind the lens of the eye, they remain out of focus. And because the vitreous is a gelatin that's not much thicker than water, it can float and dance if you try to see one directly. Hence its medical name: muscae voldados, which means "flying flies".
Where are you from?
Where do these points come from? Some are remnants of processes that took place before you were born. At the beginning of the baby's development, the inside of the eye is quite fibrous. At birth, these fibers and other cells changed into vitreous bodies. However, it may leave some cells and pieces of fiber that can float freely. There is also a canal from the optic nerve to the lens which, in the fetus, directs an artery to the lens to nourish it. The artery atrophies and is usually reabsorbed before birth, but small parts may remain.
But there are other sources as well. Even in adults, the vitreous mood is not completely frozen. It is surrounded by the delicate hyaloid membrane. It is pressed against the retina, the light-sensitive screen of fabric that lines most of the inside of the eye and captures what you see. The hyaloid membrane adheres to the retina around its leading edge. Small fibrils radiate from this suture through the vitreous humor.
With age, these fibrils start to shrink. This causes some of them to break. The vitreous also becomes more fluid, allowing broken pieces of fiber to float more freely in it. The vitreous humor itself shrinks slightly and begins to move away from the retina, eventually leaving other cell debris behind. As you get older, you will see more of these "flying flies" wandering and spinning in your field of vision.
Another source for little swimmers can be the blood vessels in the retina. A blow to the head or excessive pressure on the eyeball can cause a small vessel to release a chain of red blood cells. Red blood cells are sticky and therefore have a tendency to cluster or form a chain. Individual cells or clusters can migrate into the vitreous mood and, when they are close to the retina, be visible. Red blood cells can be reabsorbed by the body and eventually they will go away. However, they are not technically voluntary musks as they are the result of slight injury.
Does the presence of flying musk indicate that something is wrong? Not usually. People with normal eyes, even the youngest, see them and gradually learn to ignore them. However, certain conditions can indicate a hazard.
When there is danger
If you suddenly notice a lot more spots than before, it could be a sign that something is wrong. This is especially true if you also see tiny flashes of light in your eyes. These phenomena come from the retina, where light is converted into nerve impulses. Swimmers and flashes of light are usually due to retinal detachment. How did it happen?
The retina has the consistency and thickness of a damp piece of tissue paper and is almost as sensitive. Its light-sensitive layer is anchored in the back layer and in the vitreous body only at the front edge and in the optic nerve, the insertion being weaker in the focus center. The vitreous helps hold the rest of the retina in place. The eye is so hard that even a stroke usually doesn't cause the retina to tear or detach from the bed.
However, a blow can cause damage that weakens the retina in a specific area or creates a small tear or hole. This opening can also be caused by an adhesion between the vitreous humor and the retina: sudden movement or injury causes the vitreous humor to pull the retina and cause a small tear. The liquid in the glass chamber can leak behind the retina and lift you out of bed. This change causes light-sensitive nerve cells to fire, which are perceived as rays.
Bleeding, large or small, is sometimes accompanied by separation because the inner surface of the retina has its own network of blood vessels. Blood cells escape into the vitreous mood and are viewed as a sudden explosion by swimmers. Shortly afterwards, when the retina becomes detached, a veil or blind curtain invades the field of view.
Therefore, if you notice an increase in the number of spots, especially if you are accompanied by lightning, see an ophthalmologist or hospital immediately! It can be a detachment of the retina. Corrective action may not be possible after the retina has become severely detached.
Have you seen spots in front of your eyes for years but without flashes of light? There is probably nothing to worry about. Almost everyone sees these points 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 real visual impairment is testament to the robust design of the eye and the adaptability of the brain.
However, before it can be determined with certainty that there is no cause for concern, individuals with swimmers should be examined by an ophthalmologist or optometrist.
Origin of modern refraction correction
When you wear glasses or contact lenses, you have the musk in some way ready to thank you. It was her curiosity that led Frans Cornelis Donders, a well-known 19th century Dutch doctor, to conduct scientific research on the physiology and pathology of the eye. Not only did he identify some of the causes of flying muscles, he also noted that hyperopia is due to the shortening of the eyeball and that blurred vision from astigmatism is caused by uneven surfaces of the cornea and lens. His studies enabled the development of corrective glasses.