Components of the eye

The human eye is a complex organ, which is composed of many details. Each component contributes to the proper functioning of vision, thus enabling the visual process. The most important parts of the eye are presented below.

More detailed information on topics is available at the click of a mouse. The lens is located between the posterior body and the vitreous cavity. It is biconvex in shape, with the back of the eye being more curved than the front.

The lens is connected to the ciliary body via elastic fibres, the zonula fibres. Functions of the lens: The task of the lens is to bundle light rays and create a sharp image on the retina. This is achieved by the so-called accommodation, i.e. the near and far adjustment of the lens.

If you look at an object close up, the ciliary body becomes tense. This in turn leads to relaxation of the zonula fibres. This allows the lens to follow its own elasticity and take on a more spherical shape, which increases the refractive power.

Conversely, the ciliary body relaxes when observing distant objects and the zonula fibres are tensioned. This keeps the lens relatively flat, which reduces the refractive power. Diseases of the lens: With increasing age, the inherent elasticity of the lens decreases and it can no longer “ball up” as well during near accommodation.

This is the reason why many people need reading glasses in old age. In addition, condensation of proteins in the lens occurs with age. This can cause the lens to condense and lead to cataracts.

You can find detailed information on this topic at Eye Lens

Lacrimal gland Tränendru
Eye muscle
Eyeball
Iris (iris)
Pupil
Orbital cavity

The vitreous body (Corpus vitreum) is located between the lens and the retina and occupies about two thirds of the eyeball. It consists of 98% water, the remaining 2% is formed by collagen and hyaluronic acid. The nature of the vitreous body is gel-like, which, together with the pressure exerted on the surrounding structures, contributes significantly to the shape of the eyeball.

In healthy people, the vitreous body is translucent and transparent. In older people, however, there can be changes in the composition, often the vitreous body becomes increasingly fluid, which can lead to an irregular structure. A typical clinical picture is the “Mouches volantes” (German: flying mosquitoes).

These are small opacities of the vitreous body which can optically impress as flying mosquitoes. Although this can be disturbing due to the impairment of vision, it is usually harmless. The pupil is the opening in the centre of the iris through which light can pass into the interior of the eye.

Together with the iris, it is responsible for regulating the incidence of light on the retina. When it is bright, the Musculus sphincter pupillae tense up, causing a narrowing of the pupil (miosis). If it is dark, the pupil dilator muscle tightens, causing the pupil to dilate (mydriasis).

The pupil width can give important clues in medicine, therefore the “pupil reflex” is very important in many areas. The interconnection of nerve tracts leads to a narrowing of the pupil (direct reaction) when light shines into the eye. There is also an indirect reaction: the simultaneous constriction of the other eye.

For detailed information on the anatomy of the eye, please refer to PupilThe vascular skin (Uvea) consists of: It lies under the sclera and is mainly responsible for accommodation, adaptation and nutrition of the retina. The pigmentation of the vascular skin, which is different in every person, leads to the different eye colours. iris: The iris separates the anterior from the posterior chamber of the eye.

In its centre there is an opening, the pupil. The iris functions as an aperture and thus, together with the pupil muscles, regulates its width and thus the incidence of light into the rear eye (adaptation). You can find detailed information about the iris at Iris ciliary body: The iris merges into the ciliary body.

The iris merges into the ciliary body, where the ciliary muscle is located. Starting from the ciliary body, the so-called zonala fibres move towards the lens. On the one hand, they are responsible for suspending the lens and fixing it in position.

On the other hand, the near and far adjustment (accommodation) is regulated by tension and relaxation of the ciliary muscle and thus the tension of the zonula fibres (more detailed description under lens). Furthermore, the ciliary body is responsible for the production of aqueous humor. Choroid: The choroid is the largest section of the vascular skin.

It is located between the retina and the sclera at the back of the eyeball. The choroid has numerous vessels and is the tissue of the body with the best blood supply. Its main function is to supply the outer parts of the retina with oxygen and nutrients.

Are you further interested in this topic? – Iris (iris)

Ciliary body and
Choroid. The conjunctiva is a mucous membrane in the front part of the eye.

It is the connection between the eyeball and the eyelids and allows the eyeball to move in all directions of vision due to various folds. Together with the tear film, it is responsible for frictionless sliding of the eyeball. The conjunctiva is not pigmented and is relatively thin.

In addition, it is well supplied with blood, so that blood changes in the conjunctiva can also be seen. You can find more information on this topic at: ConjunctivaThe cornea is located in front of the pupil in the foremost part of the eye, has no vessels and is transparent. It consists of 70% water and is wetted with a tear film.

The cornea is the part of the eye that is responsible for about two thirds of the refraction of light. You can find detailed information on this topic at: CorneaThe retina lines the inside of the back of the eye. Its task is to receive light signals and then convert them into electrical signals, which are then transmitted to the brain.

The retina contains different types of receptors, cones and rods. Approximately 7 million cones (red, green and blue cones) are responsible for colour vision as well as vision at brightness. The 120 million rods take over at dusk and in the dark.

You can find more about this component of the eye under RetinaThe dermis (sclera) surrounds most of the eyeball. It protects it and keeps it in shape. It performs a protective function by forming a firm envelope around the eyeball and almost completely enclosing it.

To ensure this stability, it consists mainly of connective tissue. The sclera is whitish, which is why the eyeball covered by it also appears white. It is opaque.

In order that light can still reach the eye, the sclera leaves the central front part of the eye free. This is covered by the cornea. The sclera is also left out at the back of the eyeball, where the optic nerve enters.

In each eye there is an upper and a lower eyelid. Their main function is to protect the eye. The eyelids cover the eye and are quickly closed when exposed near the eye (“eyelid closure reflex”).

The eye is moistened and cleaned with tear fluid by the regular blinking of the eyelid. The tear fluid is produced by the tear gland and additional smaller tear glands. In addition to salt, glucose and proteins, the tear fluid also contains bacteria-killing substances.

The lacrimal gland is located at the upper outer edge of the eye. The blink of the eyelid spreads it throughout the eye. Then it is transported to the inner corner of the eyelid. From there, the tear fluid flows through a small passage into the nose.