AskDefine | Define eyelids

User Contributed Dictionary

English

Noun

eyelids
  1. Plural of eyelid

Extensive Definition

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes which serve to heighten the protection of the eye from dust and foreign debris. "Palpebral" (and "blepharo") means relating to the eyelids.

Anatomy

Layers

In the human eyelid, there are various layers; from superficial to deep, they are: skin, subcutaneous tissue, orbicularis oculi, orbital septum & tarsal plates, and palpebral conjunctiva. The meibomian glands lie within the eyelid and secrete the lipid part of the tearfilm.

Skin

The skin is similar to areas elsewhere, but have more pigment cells. In diseased persons these may wander and cause a discoloration of the lids. It contains sweat glands and hairs, the latter becoming eyelashes as the border of the eyelid is met.

Innervation

In humans, the sensory nerve supply to the upper eyelids is from the infratrochlear, supratrochlear, supraorbital and the lacrimal nerves from the ophthalmic branch (V1) of the trigeminal nerve (CN V). The skin of the lower eyelid is supplied by branches of the infratrochlear at the medial angle, the rest is supplied by branches of the infraorbital nerve of the maxillary branch (V2) of the trigeminal nerve.

Blood supply

In humans, the eyelids are supplied by two arches on each upper and lower lid. The arches are formed by anastamoses of the lateral palpebral arteries and medial palpebral arteries, branching off from the lacrimal artery and ophthalmic artery, respectively.

Muscles besides the Orbicularis oculi

Involuntary muscle fibers controlled by the sympathetic autonomic nervous system and open the eyelids away from each other, widening the eye aperture. The corrugator supercilii helps shield the eye from sun glare by pulling the eyebrow toward the bridge of the nose making a "roof" over the medial side of the eye and typical furrows in the forehead. The procerus muscle, on the bridge of the nose, fold the skin into transverse furrows. The Frontalis lifts the eyebrows (thus opposing the orbital portion of the orbicularis), especially when looking up. It also acts when a view is too distant or dim.

Additional images

Image:Eye makeup.jpg|Eye makeup ’ embryo rabbit. X 30.

References

eyelids in Bengali: পলক (চোখ)
eyelids in Bulgarian: Клепач
eyelids in German: Augenlid
eyelids in Spanish: Párpado
eyelids in Esperanto: Palpebro
eyelids in Basque: Betazal
eyelids in French: Paupière
eyelids in Indonesian: Kelopak mata
eyelids in Italian: Palpebra
eyelids in Hebrew: עפעף
eyelids in Latin: Palpebra
eyelids in Lithuanian: Vokas
eyelids in Dutch: Ooglid
eyelids in Japanese: まぶた
eyelids in Polish: Powieka
eyelids in Portuguese: Pálpebra
eyelids in Russian: Веко
eyelids in Finnish: Silmäluomi
eyelids in Swedish: Ögonlock
eyelids in Yiddish: אויגן לאד
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