Eyelid

Eye makeup

Eyelid

The eyelid is a delicate, multi-layered fold of skin designed to shield and safeguard the eye. A crucial component of the visual system, the eyelid, apart from the prepuce and the labia minora, boasts some of the thinnest skin in the human body. This article elaborates on its structure, function, and relevance to overall ocular health.

Eyelid affected by stye

Function

The core functions of the eyelid include:

• Regularly distributing tears and other secretions across the eye's surface, ensuring the cornea remains constantly moistened.
• Preventing the eyes from drying while asleep.
• Protecting the eye from dust, external particles, and moisture, primarily through the blink reflex.
• Serving as a defense mechanism against potential foreign bodies.

Notably, the human eyelid is adorned with a line of eyelashes, which bolster its protective capacities, especially against foreign particles and sweat.

Anatomy

File:Slide2www.JPG|Extrinsic eye muscle. Nerves of orbita. Deep dissection]]

Layers

From the outermost to the innermost layer, the eyelid comprises:

• Skin: Comparable to skin elsewhere on the body but is notably thin and has a higher concentration of pigment cells. In certain conditions, these cells may migrate, causing discoloration.
• Subcutaneous tissue
• Orbicularis oculi: A muscle responsible for eyelid movement.
• Orbital septum and tarsal plates: Provide structural support.
• Palpebral conjunctiva: A mucous membrane that lines the inner surface of the eyelid.

Within the eyelid, the meibomian glands secrete the lipid component of the tear film, essential for eye lubrication.

Innervation

Sensory innervation for the eyelids is as follows:

• Upper eyelids: Supplied by the infratrochlear, supratrochlear, supraorbital, and lacrimal nerves from the ophthalmic branch (V1) of the trigeminal nerve (CN V).
• Lower eyelids: Primarily supplied by branches of the infraorbital nerve from the maxillary branch (V2) of the trigeminal nerve, with the infratrochlear nerve serving the medial angle.

Blood Supply

Blood is delivered to the eyelids through two arterial arches in both the upper and lower lids. These arches are formed via anastomoses between the lateral and medial palpebral arteries, derivatives of the lacrimal and ophthalmic arteries respectively.

Etymology

"Palpebral" and "blepharal" are terms pertaining to the eyelids. Their origins and usage help in the anatomical and clinical description of conditions and procedures linked with the eyelid.

See also

• Eye anatomy
• Blink reflex
• Ocular system
• Blepharospasm
• Cellulitis
• Chalazion
• Dermatochalasis
• Ectropion
• Entropion
• Hay-Wells syndrome
• Nictitating membrane
• Ptosis
• Stye (Hordeolum)

Additional images

• 
  Bloodvessels of the eyelids, front view
• 
  Horizontal section through the eye of an eighteen days' embryo rabbit. X 30
• 
  Sagittal section of right orbital cavity
• 
  Sagittal section through the upper eyelid
• 
  The tarsi and their ligaments. Right eye; front view
• 
  The lacrimal apparatus. Right side

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