How big are human eyeballs

The structure of the eye

Anterior segment of the eye

The anterior segment of the eye includes:

  • Dermis
  • Conjunctiva
  • Cornea
  • Rainbow skin (iris) with ciliary body
  • lens

Connective skin, corneal skin and dermis

The Conjunctiva covers the front part of the eye including the inner sides of the eyelids. The main task of this mucous membrane is to wet the surface of the eye with tear fluid. This enables undisturbed movement of the eyeball. Leather and calluses together represent the outer shell. The cornea appears transparent and has a very high refractive power. This property is important so that we can see clearly.

Iris, ciliary body and lens

The iris with its opening - the pupil - becomes wider or narrower when the incidence of light changes and has the function of a diaphragm in the eyes.

Already knew?

When we are frightened, our pupils dilate. The release of adrenaline in the body is responsible for this. In contrast, when they sleep, they stand tightly together.

The iris goes into the side Ciliary body above. He is responsible for the suspension of the lens and its accommodation (adaptation to see clearly at different distances). The lenses in our eyes focus what we are looking at, adjusted to the different distances - comparable to the lens in a camera.

Posterior segment of the eye

The rear structure of the eye is characterized by the following components:

  • Vitreous
  • Optic nerve
  • Retina with yellow spot (macula)
  • Choroid

Already knew?

Ophthalmologists who deal with the parts of the back of the eye are also known as Retinologists.

Vitreous and choroidal membrane

Behind the lens inside the eye, the fills Vitreous the eyeball out. Among other things, it stabilizes the shape of the eye. Its interior consists of a gel-like liquid with a water content of more than 90 percent.

The retina is located, so to speak, on the back wall of the eye ("inner eye skin"). On its outside lies the Bruch membrane (Bruch's membrane), a boundary membrane between the subsequent choroid and the choroid retinal pigment epithelium (RPE) the retina. It mediates the transport of nutrients and fluids between the retinal pigment epithelium and the vascular layer of the choroid. In addition, metabolic products (“waste”) are transported away via the Bruch membrane and the subsequent RPE.

Worth knowing!

The area between Bruch's membrane and the retinal pigment epithelium is often where Druze (Deposits) arise - as in the early stages of dry age-dependent macular degeneration (AMD). They arise because the metabolism of the retinal pigment epithelium declines with age, which means that more waste products accumulate.

The layers of the retina (retina)

The retina is actually a upstream part of the brain and contains the sensory cells of the eye (light sensory cells or photoreceptors; specialized nerve cells) that receive, process and transmit the light stimulus Optic nerve forward to the brain. The retina is only about 0.1 to 0.5 millimeters thick and consists of a total of ten layers.

The actual light-sensing cells are only located in the depths of the retina, in the penultimate layer. It is about rod (Perception of light and dark; around 120 million in total) and Cones (Color vision; around 7 million in total).

One area of ​​the retina - the so-called Macula (macula lutea / yellow spot) - contains a particularly high density of cones and is the area in our eyes sharpest vision. This is especially true for the fovea, the center of the macula.

The name "yellow spot " comes from the abundant yellow color granules (lutein and zeaxanthin) stored there.1 Another special point on the retina is that blind spotthat everyone has and that does not contain any sensory cells in the eye. This is where the entry point of the optic nerve and the blood vessels that supply the eye with oxygen and nutrients is located.

Small spot, big impact!

The disease AMD only affects the macula - a patch of about five millimeters on our retina. Even if the area is small, the effects can extend to complete vision loss if no or inadequate treatment is given. This makes an early diagnosis by the ophthalmologist all the more important! You should therefore take advantage of annual check-ups from the age of 50. With timely and regular treatment, disease-related visual problems often improve.

The retinal pigment epithelium

Outwardly limits the so-called retinal pigment epithelium (RPE) the retina. This layer contains numerous dark grains of color (pigments) that absorb the remaining light. In addition, the retinal pigment epithelium supplies the inner retinal layers and the sensory cells in the eye with nutrients and oxygen.

RPE cells are also responsible for breaking down special waste products (for example "old" visual cells). The RPE also transports fluid out of the retina. In some diseases such as wet AMD or diabetic retinopathy with the accompanying symptom of diabetic macular edema (DME), this function is disturbed. This causes fluid to accumulate in the retina (edema).

By the way:

When the waste products are broken down, by-products can arise in old age. If these are deposited in the retinal pigment epithelium (RPE), so-called drusen are formed. They mark the early form of AMD.

Seeing begins in the eye - the finished image is created in the brain

How vision works can best be explained with an example: Let's assume we wanted to take a closer look at a ball. By looking directly at it, the eye first moves in such a way that the ball moves into the center of our field of vision. The light that falls on the ball is partially reflected, gets into our eyes and becomes bundled by the cornea and lens. As a result, the light falls on the point of sharpest vision in the center of the retina, the so-called macula (macula lutea, yellow spot).