[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Medial rectus [Sense organs](https://durgical.com/en/anatomy/system/sense-organs/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Medial rectus The medial rectus is one of the six muscles that move the eyeball, on the nose side of the eye; it turns the eye toward the nose. Official name: Medial rectus muscle [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=medial_rectus&side=r) Opens in the Durgical app, no sign-up needed. ## What it is One of the six muscles that move the eyeball, inside the eye socket. ## What it does Turns the eye toward the nose. ## Key points - A pure adductor; the bulkiest rectus, and the one inserting nearest the limbus (the start of the spiral of Tillaux) - Both medial recti contract together in convergence for near vision, with accommodation and pupil constriction (the near triad) - Internuclear ophthalmoplegia: a lesion of the medial longitudinal fasciculus stops the medial rectus in side gaze but not in convergence; in a young adult it suggests multiple sclerosis - The second muscle most often enlarged in thyroid eye disease, after the [inferior rectus](https://durgical.com/en/anatomy/inferior-rectus-muscle/) ## Key facts **Origin** [Common tendinous ring](https://durgical.com/en/anatomy/common-tendinous-ring/) (annulus of Zinn) **Insertion** [Sclera](https://durgical.com/en/anatomy/sclera/) medially, ~5.5 mm behind the limbus **Action** Adduction **Nerve** Oculomotor nerve (III), inferior division **Blood supply** Ophthalmic artery (muscular branches) ## Relations **Medial** Thin medial orbital wall (lamina papyracea of the [ethmoid bone](https://durgical.com/en/anatomy/ethmoid-bone/)), with the [ethmoid cells](https://durgical.com/en/anatomy/anterior-cells-of-ethmoid-bone/) behind it **Above** [Superior oblique](https://durgical.com/en/anatomy/superior-oblique-muscle/); between the two run the [ophthalmic artery](https://durgical.com/en/anatomy/ophthalmic-artery/), the nasociliary nerve and their ethmoidal branches **Lateral** Globe and [optic nerve](https://durgical.com/en/anatomy/optic-nerve/); the inferior division of the [oculomotor nerve](https://durgical.com/en/anatomy/oculomotor-nerve/) enters its lateral (ocular) surface ## How to find it Its tendon inserts closest to the [cornea](https://durgical.com/en/anatomy/cornea/), about 5.5 mm from the medial limbus, so it is the easiest rectus to reach through a nasal conjunctival incision. Further back it runs along the medial wall next to the paper-thin lamina papyracea of the ethmoid, with the superior oblique above it. ## Examination - H-pattern: the person looks straight in toward the nose; weak adduction points to the medial rectus or the oculomotor nerve (III) - Convergence: a target brought toward the nose; adduction that fails in side gaze but works in convergence places the lesion in the medial longitudinal fasciculus - Cover–uncover and alternate cover tests: an eye that moves out to take up fixation was turned in (esotropia); one that moves in was turned out (exotropia) ## On imaging Coronal CT or MRI of the orbits shows enlargement of the belly in thyroid eye disease and crowding of the optic nerve by enlarged medial recti at the apex; CT shows the lamina papyracea in sinus disease and medial wall fractures. ## Common problems - Sixth-nerve palsy: the eye cannot turn out, causing side-by-side double vision. - Strabismus (squint) when the eye muscles are unbalanced. ## How it is diagnosed Eye movement and alignment tests; scans if a nerve palsy is new. ## Treatment - Prisms or patching; botulinum toxin; eye muscle surgery to rebalance the muscles. ## Clinical notes - Strabismus in children: infantile esotropia appears in the first months; accommodative esotropia appears later in long-sighted children and improves with glasses. Surgery often weakens or tightens the horizontal recti - An untreated squint or unequal focus in early childhood causes amblyopia: the brain suppresses one eye and its vision fails to develop; treatment works only while the visual system is still maturing - Endoscopic sinus surgery can breach the lamina papyracea and injure the medial rectus; ethmoid sinusitis spreads to the orbit by the same route - A medial wall fracture can trap the muscle and limit abduction ## Development Forms from head mesoderm around the optic stalk, within the common mass that gives rise to all the muscles of the oculomotor nerve. ## Related conditions - [Graves disease (hyperthyroidism)](https://durgical.com/en/conditions/graves-disease/) - [Strabismus and amblyopia](https://durgical.com/en/conditions/strabismus-and-amblyopia/) - [Thyroid eye disease (Graves orbitopathy)](https://durgical.com/en/conditions/thyroid-eye-disease/) ## Test yourself Think of the answer, then tap the question to see it. ## What is the action and nerve supply of the medial rectus? Pure adduction; supplied by the inferior division of the oculomotor nerve (III). ## What is internuclear ophthalmoplegia, and what does it suggest in a young adult? A medial longitudinal fasciculus lesion: the medial rectus fails in side gaze but works in convergence; in a young adult it suggests multiple sclerosis. ## Why can endoscopic sinus surgery injure the medial rectus? It lies against the thin lamina papyracea of the ethmoid; breaching it reaches the muscle, and ethmoid sinusitis spreads to the orbit the same way. ## What happens to an eye with an untreated squint in early childhood? Amblyopia: the brain suppresses that eye and its vision fails to develop; treatment works only while the visual system is maturing. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/medial-rectus-muscle/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** musculus rectus medialis TA2 2044 **Official Spanish (DeCS)** Músculo recto medial DeCS D009801 **English (TA2)** Medial rectus muscle **Also called** internal rectus · musculus rectus nasalis bulbi ## Related - [Oculomotor nerve (III)](https://durgical.com/en/anatomy/oculomotor-nerve/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=9987&filter=ths_termall&q=Oculomotor%20Muscles); [Anatomy, Head and Neck: Eye Medial Rectus Muscles](https://www.ncbi.nlm.nih.gov/books/NBK519026/); [Anatomy, Head and Neck, Eye Extraocular Muscles](https://www.ncbi.nlm.nih.gov/books/NBK519565/); Anatomy of the Human Body (20th ed.): The Accessory Organs of the Eye (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain; Anatomy of the Human Body (20th ed.): Development of the Muscles (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain. ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/medial-rectus-muscle/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/medial-rectus-muscle/