How the eye works

How is the eye structured? How does it work that we see objects clearly? Here you will find a lot of interesting information on the subject of eyes

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Anatomy of the eye

The eye is a highly complex organ and is responsible for one of our five senses: sight. It is composed of:

  • eyeball
  • Eyelids and muscles
  • Lacrimal system
  • and optic nerve

In order to be able to see things, light must first fall into the eye and be refracted in such a way that it hits the retina unhindered. With the help of the optic nerves, the information from the light waves is transmitted to the brain. It is only here that what is seen can be perceived at all. For this process, the individual parts of the eyeball must work well together:

  • Cornea
  • pupil
  • lens
  • Vitreous
  • Retina
  • Optic nerve

The pupil regulates the incidence of light. The cornea, lens and vitreous body determine the refractive power. The lens bundles the rays, reduces the image and projects it - turned upside down - onto the retina. The light sensory cells (visual cells or photoreceptors) are located on the retina and allow us to recognize colors, contrasts and much more. The photoreceptors convert the incident light into electrical impulses that are sent to the brain via the optic nerve. Only our brain turns the transmitted image over and lets us perceive it the right way round.

In our interactive graphic you can get to know the individual components of the eye and their function in more detail.


The pupil regulates the incidence of light into the eye. It works in a similar way to the aperture on a camera. In the dark, the pupils are widened; when looking into the light, they narrow.


The conjunctiva surrounds the cornea and the visible white part of the eye. It reaches to the lids. Conjunctivitis (conjunctivitis) can be very uncomfortable.


The light falls through the clear cornea on the pupil and lens. The cornea makes up most of the refractive power of the eye and is therefore an important part of the optical apparatus.


It is the part of the eye around the pupil that we perceive as brown, blue, gray or green.


The lens is the part of the eye that can change its refractive power and thus ensures that we can see well both near and far. In the case of cataracts, it becomes cloudy.


The vitreous is a transparent, jelly-like mass that fills the space between the lens and retina.


The dermis is the outermost layer of the eyeball. Part of her is visible as the white of her eyes.


In the choroid there are mainly vessels that supply the outer layers of the retina with blood.


The sensory cells (photoreceptors) that enable us to see are located in the retina. They convert incoming light into electrical impulses that are passed on to the brain via nerve fibers.

Optic nerve

It bundles the nerve fibers coming from the retina and represents the connection to the brain.

Blood vessels of the retina

Why can we see clearly?

Not all living things see the world the same way. For example, insects can see ultraviolet light. Dogs can only recognize colors to a limited extent and, depending on the shape of their head, can see quite blurred. Humans, on the other hand, can see clearly in the distance as well as up close. Our eyes adjust the focus in a flash. From things ten centimeters from our face to things 100 meters away. This complicated process is called accommodation. The following video explains exactly how this works.

What is the function of the eyelids?

The eyelids protect the sensitive organ from foreign bodies and too much light. If a light source dazzles, we automatically squint our eyes and thus protect the light-sensitive nerve cells on the retina. If something touches the cornea of ​​the eye, the so-called eyelid closing reflex is triggered: We involuntarily close our eyes to protect them.

Should a grain of sand or a small insect get in your eye, you will find first aid tips here.

In addition, the eyelids distribute the tear fluid on the eyeball. Small foreign bodies that have reached the cornea are quickly flushed towards the tear duct and out of the eyes. The illustration shows which path the tear fluid takes.

© W & B / Ulrike Möhle

If the channels are blocked or too narrow, our eyes "overflow" and water. Something similar can happen if a constant stimulus such as smoke or strong sunlight stimulates the flow of tears.

Common eye diseases

However, numerous eye diseases can affect our vision. The ametropia are among the most common. These can be divided into

  • myopia
  • Farsightedness

Presbyopia is actually not an eye disease, but a normal symptom of old age.

According to the professional association of ophthalmologists in Germany, 63.4% of Germans over the age of 16 are treated for ametropia. That's 40.1 million people.

Previous illnesses and poor eyesight

Some diseases can also lead to poor eyesight. The most common pre-existing conditions include diabetes mellitus and high blood pressure. Both have different effects on the retina. If it is damaged, the nerve cells on it cannot correctly transmit the light stimuli to the brain. The result: blind or blurred spots appear, in the worst case blindness occurs.