Eyelids and eyelashes
EYELIDS AND EYELASHES ANATOMYThe eyelids are also known as the palpebrae, and are formed by the reinforced folds of skin that are attached to the slight skeletal muscles which permit movement. The orbicularis oculi muscle assists in the control of the eyelids, and it receives additional assistance from the levator palpebrae superioris muscle, which is designated to the upper eyelid and explains why the upper lid has more movement options than the lower lid.
EYELIDS AND EYELASHES STRUCTUREWhen the eyelids draw down over the eye, or the eyes “close,” it is the result of the orbicularis oculi muscle contracting. When the levator palpebrae superioris muscle contracts, the result is the “opening” of the eye, or the eylid drawing back up over the eye to reveal the eyeball.
The eyeball is protected by the eyelid, both from desiccation and from impalement. When the eyelid blinks, which occurs every 7 seconds or so, fluid flushes the eyeball and keeps it moisturized. The eyelid also reflexively blinks when the eye senses a particle that threatens to enter it. The eyelid will usually blink reflexively when the eye is adjusting to a new line of vision to help prevent the initial blurry vision that can occur from refocusing too quickly.
The small but detectable space between the upper and the lower eyelid is known as the palpebral fissure. When the eyes are closed, this fissure appears to be nothing more than a line of connection. When the eyes are open, the fissure takes on an elliptical shape. The small medial and lateral angles where the eyelids conjoin is known as the commissure of the eye. The medial commissure is the larger of the two, and is noted by a small elevation of red flesh which is known as the lacrimal caruncle. The lacrimal caruncle is responsible for creating the white secretions that get caught at the corner of the eye, usually during sleep, thank to the sebaceous and sudoriferous glands.
The eyelids each house their own tarsal plate as an added shield of protection. They also have conjunctiva and tarsal glands. The tarsal plate is comprised of connective tissue, which is vital in maintaining the general shape of the eyelids. The tarsal plate house the tarsal glands, which are specialized sebaceous glands which can be detected along the inner surface of the eyelid, visible to the naked eye.
The ducts of the tarsal glands open up along the edges of the eyelids and secrete and oily substance which protect the eyelids from becoming stuck to each other. Additional sebaceous glands can be found along the base of the hair follicles which create the
EYELIDS AND EYELASHES FUNCTIONSEach eyelid is the perfect anchoring ground for eyelashes, one row per eyelid. Each single eyelash is embedded into the eyelid by the root, which anchors into a root hair plexus. This give the eyelash hairs additional sensitivity to snap the eye closed in the event of an airborne particle reaching the eye.
The eyelashes belonging to the upper lids and the lower lids vary from each other. The upper lid eyelashes are longer, tend to curve in an upward direction, and are more noticeable than the lower lid eyelashes, which are shorter and tend to be stumpy without much curve.