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The intraocular muscles are responsible for the protraction and retraction of the eyelids and reaction to light and pupil accommodation. [2] They're different to the extraocular muscles that are outside of the eye and control the external movement of the eye.
An eyelid is a thin fold of skin that covers and protects the eye. The levator palpebrae superioris muscle helps in the movement of eyelid. The human eyelid features a row of eyelashes along the eyelid margin, which helps in protection of the eye from dust and foreign debris. The main function of eyelid is to keep the cornea moist and clean.
The double eyelid crease forms due to connective tissue anchoring between the eyelid skin and the underlying tarsal plate. The presence or absence of a crease is influenced by genetics, skin elasticity, and muscle function. However, eyelid creases can shift over time due to factors like aging, swelling, or repetitive tension.
The medial palpebral ligament (medial canthal tendon) is a ligament of the face. It attaches to the frontal process of the maxilla , the lacrimal groove , and the tarsus of each eyelid . It has a superficial (anterior) and a deep (posterior) layer, with many surrounding attachments.
The seventh muscle is the levator palpebrae superioris muscle. When the muscles exert different tensions, a torque is exerted on the globe that causes it to turn, in almost pure rotation, with only about one millimeter of translation. [8] Thus, the eye can be considered as undergoing rotations about a single point in the centre of the eye.
The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and duct, the eyelids, medial and lateral palpebral ligaments, cheek ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves.
The extraocular muscles develop along with Tenon's capsule (part of the ligaments) and the fatty tissue of the eye socket (orbit). There are three centers of growth that are important in the development of the eye, and each is associated with a nerve. Hence the subsequent nerve supply (innervation) of the eye muscles is from three cranial ...
Damage to this muscle or its innervation can cause ptosis, which is drooping of the eyelid. [4] [5] Lesions in CN III can cause ptosis, [5] because without stimulation from the oculomotor nerve the levator palpebrae cannot oppose the force of gravity, and the eyelid droops.