Lid
 lid |
The lid is a thin, from muscles and skin existing fold, which covers an eye. The eyelid distributes tear liquid with each eyelid impact. It cleans thereby the cornea/callosity and moistens it, so that this remains clean. Additionally the closed eyelid protects the eye against mechanical influences (eyelid conclusion reflex).
If the lid is missing, one speaks of a Ablepharie.
Table of contents |
basic structure
it gives an upper (Palpebra superior) and a lower lid (Palpebra inferior). Between both is the eyelid column (Rima palpebrarum). Both lids collide at the sides in the eyelid angle (Angulus oculi or Canthus). The lids are covered on the inside by the binding skin (Konjunktiva).
An additional binding skin fold in the nose-lateral eye angle becomes also as pitch skin (Plica semilunaris conjunctivae, Membrana nicitans) or 3. Lid (Palpebra tertia) marks. With humans it is only rudimentary. With the remaining mammals it is so large that it can put with certain illnesses before the entire eye. With many other vertebrate animals, e.g. Sharks, reptiles and birds, it is transparency and can like an eye protector before the eye be folded.
internal structure
the eyelids consist outside of body skin, with approx. 5 mm at the eyelid is very thin. At the edge of eyelid the lashes ( cilia) sit. Around the lashes there are several glands:
- Glandulae of ciliares (Moll glands)
- Glandulae sebaceae (Zeiss glands)
- Glandulae of tarsales (Meibom glands, Tarsaldrüsen)
the glands form the so-called “eye butter”, a secretion, which prevents an overflowing of the tear liquid over the eyelid edge. Against the morning usually dried up yellowish secretion remainder inside eyelid angles one rubs as “sleep” from the eyes. Infections of the glands can to a barley grain (Hordeulum externum - Zeiss and. Moll glands, Hordeulum internum - Meibom glands) lead. Granulating inflammations of the Meibom glands are called hail (Chalazion).
The central layer consists of close connective tissue. It forms the eyelid plate (Tarsus). Into the central layer smooth musculature is embedded (Musculus tarsalis). The pitch skin is supported from a cartilage.
The rear side of the lids is covered of the binding skin.
the various movements
and closing the eyelids make several transversetouched muscles for muscles possible of the lids:
- Musculus levator palpebrae superioris
- Musculus orbicularis oculi
- Musculus retractor anguli oculi lateralis
- Musculus levator anguli oculi medialis
- Musculus malaris
- Musculus frontalis
innervation
the sensitive innervation is made by several branches of the Nervus trigeminus.
The Musculus tarsalis becomes sympathetic internal fourth. A damage leads to a Herunterhängen of the eyelid (ptosis) and is one of the symptoms with the horn he syndrome.
The outside transversetouched musculature becomes of the Nervus facialis, the Musculus levator palpebrae superioris by the Nervus oculomotorius internal fourth.
