Structure of the eye

Synonyms in a broader sense

Medical: Organum visus eye structure, eye anatomy, eye English: eye

Introduction

The human eye or the eye skin can be roughly divided into 3 layers: Specialized pigment cells (melanocytes) stored in the iris (rainbow skin) are responsible for the colour of the eye visible from the outside. The amount of pigment alone determines the colour of the eyes: brown eyes contain a lot of pigment, blue and grey eyes contain little. Belonging to the middle eye skin (the so-called tunica vasculosa bulbi, the vascular skin), the iris borders on the posterior eye skin, the retina.

In addition, the radiation body (lat. corpus ciliare, ciliary body), which is important for the closeness of the optical apparatus, and the choroid, which supplies the outer retina with blood (choroidea), belong to the middle eye skin. A further important function of the radiating body is the formation of the aqueous humor.

Furthermore, this structure serves to fix the lens, which is suspended on ligaments behind the iris. The entirety of the structures belonging to the middle eye skin is also called uvea. – Outer eye skin (sclera and cornea)

  • Middle eye skin (deer skin, ciliary body, choroid)
  • Inner eye skin (retina)

The lens

The lens is the second refractive, transparent organ in the eye besides the cornea. In contrast to the latter, however, its refractive power is variable, so that a sharp image of near and far objects can be projected onto the retina. This is due to the muscularly controlled length of the suspension ligaments of the lens: If they slacken, the lens curves passively due to its own elasticity and the refractive power increases: Near objects can be seen sharply with the eye.

If the suspension bands are tightened, the lens becomes flatter again as the refractive power decreases. If the ratio of the lens refractive power does not match the length of the eyeball (i.e. the distance between the retina), a sharp image cannot be produced on the retina. These eye diseases (ametropia) are corrected by increasing or decreasing the refractive power of the lens: In the case of long-sightedness (hyperopia), the light is focused behind the retina, corresponding to an insufficient refractive power of the eye or an eyeball that is too short.

Therefore, this design, a converging lens (with positive refractive power, measured in diopters) can help. In myopia, the refractive power of the eye is too great or the eyeball is too long and the sharp image is projected in front of the retina. The treatment is therefore carried out with diffusion lenses (with negative refractive power).

The structure of the back wall of the eyeball is lined on the inside by the retina. It consists mainly of nerve cells, which are responsible for converting light stimuli into electrical signals and transmitting them to the brain. This section of the eye, also known as the fundus, is accessible to medical examination by looking through the medically dilated pupil (funduscopy).

The most important structures are the: The blind spot is the part of the retina where the bundled fibres of all nerve cells unite to form the optic nerve (hence the Latin name discus nervi optici). No nerve cells necessary for the visual process are located there. Nevertheless, the blind spot is not noticeable as a loss of visual field: The missing optical information is replaced by the other eye, controlled by the brain.

On the other hand, the density of nerve cells is particularly high at the yellow spot: this is why it is also called the “spot of sharpest vision. This is why age-related changes, for example, have a particularly strong effect on vision (see diseases: age-related macular degeneration). Important for the visual process is the so-called visual pigment (visual dye).

It is located in the extensions of the nerve cells known as photoreceptors and changes its chemical structure when the eye is illuminated, thereby generating electrical signals. Vitamin A is necessary for this process known as transduction (conversion), as it is a component of the visual pigment. Vitamin A deficiency therefore leads to night blindness (hemeralopia).

You can read more about this disease under night blindness. The eyelid, one of the auxiliary structures of the eye, is controlled (innervated) by the facial nerve (lat. Nervus facialis).

Metabolic processes or injuries that lead to damage of the facial nerve are therefore noticeable by reduced or missing eyelid closure. 30 glands contained in the eyelid produce a fatty film which protects against evaporation of the tear film and thus prevents the eye from drying out. The tear fluid itself is produced by the lacrimal gland located in the lateral, bony orbit of the eye (per day about 1⁄2 ml.)

Besides water, the most important components are proteins that kill bacteria. – blind spot and the