The human eye

Synonyms in a broader sense: Medical: Organum visus English: eye


The eye is responsible for transmitting visual impressions from the environment to the brain and is anatomically still counted as an outsourced structure of the brain. The eye consists of the eyeball (lat. Bulbus oculi; this means “the eye” in the colloquial sense) and the associated auxiliary equipment, e.g. eyelids, eyelashes, tear organs.

Anatomy and function

The eyeball has an almost spherical shape and measures about 2.4 cm in diameter. In its anterior section the refractive structures of the eye are found: lens and cornea (see below), while the posterior section is formed by the retina, which is responsible for processing stimuli and converting them into electrical signals. The main component of the eyeball is the gelatinously soft vitreous body (lat.

corpus vitreum). It consists of 98% water and a fine network of connective tissue. It serves to maintain the inner shape of the eye and to protect the lens and retina from changes in position.

In old age, there is often harmless but disturbing clouding of the vitreous body, which is perceived as dark spots (“mouches flies”). Are you interested in this topic further?characteristic is the three-layer structure of the wall covering the eyeball. A distinction is made between an outer, a middle and an inner eye skin.

The outer eye skin represents “the white” in the eye and is also called sclera. In the area of the anterior surface of the eye it merges into the transparent cornea (lat. Cornea).

Clouding of the cornea is pathological – like cataracts, for example. They lead to a decrease in visual acuity, which can even lead to blindness (see diseases below). Due to its strong curvature, it is of outstanding importance for the visual process.

With a refractive power that exceeds that of the lens many times over, the cornea plays a decisive role in the sharp imaging of the surroundings on the retina by bundling incident light rays (focusing). In contrast to the lens, however, its refractive power is not variable. The cornea itself is free of blood vessels and is therefore nourished by diffusion from the front from the covering tear film and from the back from the so-called anterior chamber of the eye.

The latter represents a (“chamber”-) liquid-filled cavity, which is formed by the cornea as anterior wall and the iris (iris) as posterior wall. The transition between the two forms an acute angle, the chamber angle containing the small veins. These blood vessels ultimately form the outflow for the continuously renewed aqueous humor.

This water comes from the posterior chamber of the eye, which is connected to the anterior chamber via the iris. If the aqueous humor cannot drain off properly due to an obstruction or increased formation, the intraocular pressure increases and damage to the optic nerve and retina is imminent. This disease is called glaucoma and can have various causes.

Q The transparency of the cornea is a masterpiece of nature: It is guaranteed by the exact arrangement of 50 layers of connective tissue fibres with a precisely defined regular alignment to each other and a constant water content. Injuries to the superficial cornea heal quickly and without scarring, as there is always a quick supply of stem cells at the transition to the white eye skin. These enable the complete renewal of the surface cells once a week. This is particularly important because the cornea is exposed to environmental influences such as radiation, direct injuries, bacteria, viruses and fungi without protection due to its location.