Together, these muscles are capable of moving the eye in almost any direction. The extrinsic eye muscles extend from the bony orbit to the sclera of the eye and are surrounded by a significant amount of periorbital fat. This is why the nose gets stuffy when an individual cries. The nasolacrimal duct carries lacrimal fluid into the nasal cavity. The two lacrimal canals lead to the lacrimal sac and then into the nasolacrimal duct. From there, the tears enter two small openings called lacrimal punta, and then they pass into two ducts knowns as the lacrimal canals. The lacrimal glands, each about the size of an almond, secrete the lacrimal fluid that drains into six to 12 excretory ducts that empty the fluid onto the surface of the conjunctiva of the upper eyelid. The lacrimal apparatus produces and drains lacrimal fluid, or tears, from the eye. It does not cover the cornea, which is a transparent region that forms the outer anterior surface of the eye. The conjunctiva is a thin, protective mucous that covers the sclera of the eye. The tarsal plate is composed of connective tissue that gives support to the eyelids. The whitish material that sometimes accumulates in that region is from these glands. The lacrimal caruncle is the small, pink, globular spot at the inner corner, or the medial canthus, of the eye. The space between the upper and lower eyelid that exposes the eyeball is the palpebral fissure. Twitches of the eyelids are a common and usually harmless symptom that can be caused by stress and fatigue. Beneath this layer is a donut-shaped muscle that encircles the eye called orbicularis oculi, which is innervated by the 7th cranial nerve, and is in charge of closing the eyelids. The upper eyelid exhibits a greater range of movement than the lower eyelid as it contains the levator palpebrae superioris muscle, a muscle innervated by cranial nerve 3 in charge of lifting the eyelid. The eyelids, also known as the palpebrae, cover the eyes during sleep, protect the eyes from excess light and possibly objects, and spread lubricating secretions over the eyeball. įunctions of the Accessory Structures of the Eye The accessory structures of the eye include the eyelids, eyelashes, eyebrows, the lacrimal apparatus, and extrinsic eye muscles.
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