Eye Lids appearance
Eye Lids APPEARANCE
The appearance of the human upper eyelid often varies between different populations. The prevalence of an epicanthic fold covering the inner corner of the eye may reach up to 90% in East Asian and Southeast Asian populations and is found in varying degrees in others. Separately, but also similarly varying between populations, the crease of the remainder of the eyelid may form either a "single eyelid", a "double eyelid", or an intermediate form.
Eyelids can be found in other animals, some of which may have a third eyelid, or nictitating membrane. A vestige of this in humans survives as the plica semilunaris
Layers - The eyelid is made up of several layers; from superficial to deep, these are: skin, subcutaneous tissue, orbicularis oculi, orbital septum and tarsal plates, and palpebral conjunctiva. The meibomian glands lie within the eyelid and secrete the lipid part of the tear film.
Skin - The skin is similar to areas elsewhere, but is relatively thin and has 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.The skin of the eyelid contains the greatest concentration of sebaceous glands found anywhere in the body.
Nerve supply- 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 -The eyelids are supplied with blood by two arches on each upper and lower lid. The arches are formed by anastomoses of the lateral palpebral arteries and medial palpebral arteries, branching off from the lacrimal artery and ophthalmic artery, respectively.
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