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StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The muscles of the eye space integral to its role and motion. Muscle directly associated with the eye encompass the extraocular muscle which control the external movement of the eye; the intraocular muscles, which are responsible because that pupil accommodation and reaction come light; and also the protractor and retractors that the eyelids. Deficits in the muscles or the nerves innervating these muscles can an outcome in functional handicap of the involved structures.


Structure and also Function

The intraocular muscles include the ciliary muscle, the sphincter pupillae, and also the dilator pupillae.<1> The ciliary muscle is a smooth muscle ring the controls house by altering the shape of the lens, and also controlling the flow of aqueous humor right into Schlemm"s canal. The ciliary muscle is attached come the zonular fibers, which suspend the lens. Upon contraction of the ciliary muscle, the tension on the lens i do not care lessened, which reasons it to take on a much more spherical form to emphasis on near objects. Be safe of the ciliary muscle has actually the the contrary effect, optimizing distant focus. The sphincter pupillae and also dilator pupillae are also composed of smooth muscle. The sphincter pupillae encircles the pupil and also is responsible for the constriction that its diameter, while the dilator muscle is i ordered it radially and also increases the pupillary diameter.

There room three main axes of ocular movements: vertical, transverse, and also anteroposterior. Rotation roughly the vertical axis results in one of two people adduction (medial movement) or kidnapping (lateral movement) that the eye. Rotation around the transverse axis reasons elevation (superior motion) or depression (inferior motion). The anteroposterior axis allows the activity of the remarkable pole the the eye medially (intorsion) or laterally (extorsion). The rotations roughly the anteroposterior axis enable the eye to readjust to the tilting the the head.

The medial rectus muscle is responsible because that medial rotation roughly the upright axis, and also the lateral rectus lateral rotation. The remarkable rectus muscle generally elevates the eye and also contributes come adduction and also intorsion. The inferior rectus depresses and also laterally rotates the eye and also contributes to adduction and also extorsion. The superior oblique abducts, depresses, and also medially rotates the eye, when the inferior oblique abducts, elevates, and also laterally rotates the eye. The four rectus muscle originate indigenous the Annulus that Zinn and are approximately 40mm in length. Lock insert onto the sclera a few millimeters indigenous the limbus. The worse oblique originates native the orbital floor and also inserts top top the sclera in the inferotemporal globe. The premium oblique originates in the posterior orbit and travels medially prior to inserting on the sclera in the superotemporal globe.<1>

The main retractor that the top eyelid is the levator palpebrae superioris, i beg your pardon is a bones muscle. The remarkable tarsal muscle (Müller"s muscle) is made up of smooth muscle and also contributes come the elevation of the top eyelid. In the lower eyelid, the retractors room the capsulopalpebral fascia and the inferior tarsal muscle. The orbicularis oculi muscles space the main protractors (closure) the the eyelids. It is a flat, ringlike band of skeleton muscle neighboring the anterior orbit written of three parts: the orbit portion, the palpebral portion, and also the lacrimal portion.


Embryology

The ciliary muscle and both pupillary muscles are cranial neural comb derivatives and also develop indigenous the mesenchyme of the choroid.

The extraocular muscles, including the levator palpebrae superioris, are derivatives of periocular mesenchyme. Five of the 6 extraocular muscle originate at the annulus that Zinn (a tendinous ring), when the inferior oblique originates ~ above the orbital portion of the bony maxilla. The annulus that Zinn overlies the premium orbital fissure and the optic foramen.<2> Three patriotic somites discovered anterior come the developing ear that the embryo room responsible because that the advancement of the extraocular muscles. These 3 somites correspond with the distribution of cranial nerves III, IV, and VI.

The orbicularis oculi derive from mesenchyme of the second pharyngeal arch, and also forms from mesoderm that the eyelid.


Blood Supply and also Lymphatics

The bulk of the blood it is provided to the orbit is provided by the ophthalmic artery, i m sorry branches off of the inner carotid artery. A branch of the exterior carotid artery, the infraorbital artery, also contributes blood supply to the orbit floor. There are countless branches that the ophthalmic artery, consisting of the central retinal, supraorbital, supratrochlear, lacrimal, dorsal nasal, short posterior ciliary, lengthy posterior ciliary, posterior ethmoidal, anterior ethmoidal, and also anterior ciliary (off that the muscular branches that the ophthalmic artery) arteries. Except for the central retinal artery and also the ciliary arteries, which supply intraocular structures, these branches, and the infra-orbital artery turn off of the outside carotid, all contribute to the vascular supply of the extraocular muscles and also structures. The superior and also inferior ophthalmic veins room responsible for venous drainage the the orbit.

The existence and also location of orbital and eyelid lymphatics room a present area of ongoing research and debate.


Nerves

The extraocular muscles are innervated by nerves that enter the orbit v the exceptional orbital fissure. The oculomotor nerve (CN III) divides into superior and also inferior branches and innervates the superior, medial, and inferior recti, the levator palpebrae superioris, and the worse oblique. It also carries presynaptic parasympathetic yarn to the ciliary ganglion. Sympathetic yarn of CN III contribute to upper eyelid retraction by innervation the the premium tarsal muscle (Müller"s muscle). The trochlear nerve (CN IV) innervates the remarkable oblique, and also the lateral rectus receive innervation indigenous the abducens nerve (CN VI). Innervation to the orbicularis oculi is through the temporal and zygomatic branches of the facial nerve (CN VII).

The ophthalmic nerve (branch the CN V1) branches into the frontal, nasociliary, and lacrimal nerves. The ciliary ganglion is consisted of of postsynaptic parasympathetic nerve cell bodies connected with the ophthalmic nerve. The quick ciliary nerves originate from the ciliary ganglion and carry parasympathetic and also sympathetic yarn to the iris and ciliary body. The long ciliary nerves branch off of the nasociliary nerve and also carry postsynaptic sympathetic yarn to the dilator pupillae and also afferent fibers from the cornea and iris. The sphincter pupillae is parasympathetically-stimulated while the dilator pupillae is sympathetically-stimulated.


Surgical Considerations

Strabismus surgery is carry out on the extraocular muscles and aims to exactly the misalignment the the eyes. The main varieties of strabismus surgical procedure involve loosening or weakening, tightening or strengthening, and also transposition or repositioning. Long-term or flexible sutures are both options. Flexible suture surgery entails the placement of a stitch that have the right to be shortened or lengthened throughout a short period following the surgical procedure to change for appropriate alignment. Loosening procedures incorporate recession or the movement of the insertion of an ocular muscle posteriorly towards its origin, tenotomy, tenectomy, myotomy, and also myectomy. Tightening procedures incorporate resection in which a distal section of the ocular muscle is removed before reattachment of the muscle to the eye, development of the muscle insertion come a much more anterior position, and also tucking.


Clinical Significance

Strabismus occurs when the eyes room misaligned together that things is not concentrated simultaneously ~ above the fovea of each eye. A phoria is identified as the turning of one eye in (esophoria) or the end (exophoria) upon occlusion of opposing eye. Phorias are often asymptomatic however may degenerate right into tropias. Tropia is a spontaneous eye turn in the lack of an ocular occlusion. Tropias space often much more prevalent with tiredness as phorias become an ext pronounced, and the ability to compensate decreases. Specific drugs can result in temporary tropias.<3>

Amblyopia results as soon as the vision in among the eyes becomes reduced because the eye and the mind are no working together correctly. Strabismic amblyopia is the result of eye misalignment and also is treated at first by patching the good eye to pressure the son to usage the amblyopic eye, and may ultimately require strabismus surgery. After age five, the is challenging to turning back amblyopic vision.<4>

Extraocular muscle paralysis can occur due to disease or injury and also may involve one or lot of muscles.<5> Oculomotor nerve palsy affect the majority of the extraocular muscles, and the sphincter pupillae and also the levator palpebrae superioris. CN III palsy presents v a "down and out" placing of the eyeball that the influenced side with a totally dilated and also non-reactive pupil. Abducens nerve palsy affects only the lateral rectus muscle. The presents together an i can not qualify to abduct the eye ~ above the impacted side, with the eye reverting come an adducted position as result of the unopposed traction of the medial rectus.<6><7><8><9><10>


Review Questions


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Figure

Extraocular muscles. Added by OpenStax, License: CC by 3.0


References

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