[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/) › Inferior rectus [Sense organs](https://durgical.com/en/anatomy/system/sense-organs/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Inferior rectus The inferior rectus is one of the six muscles that move the eyeball, under the eye inside the eye socket; it turns the eye down and slightly in. Official name: Inferior rectus muscle [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=inferior_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 down (and slightly in). ## Key points - A pure depressor when the eye is abducted; in primary gaze it also extorts and adducts - The muscle most often trapped in an orbital floor (blowout) fracture: upgaze is limited and the person sees double looking up - Usually the first and most enlarged muscle in thyroid eye disease; a tight inferior rectus holds the eye down and limits upgaze - Its sheath sends the capsulopalpebral fascia to the lower lid, so the lid drops on downgaze; operating on the muscle can change lower lid height ## 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/) below, ~6.5 mm behind the limbus **Action** Depression (best in abduction); extorsion, adduction **Nerve** [Oculomotor nerve (III)](https://durgical.com/en/anatomy/oculomotor-nerve/), inferior division **Blood supply** [Ophthalmic artery](https://durgical.com/en/anatomy/ophthalmic-artery/) (muscular branches) ## Relations **Below** Orbital floor ([maxilla](https://durgical.com/en/anatomy/maxilla/)), with the infraorbital nerve and vessels in their groove and canal; below the floor, the [maxillary sinus](https://durgical.com/en/anatomy/maxillary-sinus/) **Above** Globe and [optic nerve](https://durgical.com/en/anatomy/optic-nerve/) **Lateral** The nerve to the [inferior oblique](https://durgical.com/en/anatomy/inferior-oblique-muscle/), which runs forward along its lateral border; the [lateral rectus](https://durgical.com/en/anatomy/lateral-rectus-muscle/) further out **In front** Near its insertion the inferior oblique crosses below it; their sheaths fuse into the suspensory (Lockwood) ligament ## How to find it Its tendon inserts about 6.5 mm behind the lower limbus and is reached through the lower [fornix](https://durgical.com/en/anatomy/fornix/). From below it lies on the orbital floor, near the thin bone beside the infraorbital groove; toward the front the inferior oblique passes under it, between the muscle and the floor. ## Examination - H-pattern: the person looks out, then down; weak depression in abduction isolates the inferior rectus - Forced duction test: under topical anaesthesia the eye is grasped and moved; resistance to moving it up means a mechanical restriction (trapped or fibrotic inferior rectus), not a nerve palsy ## On imaging Coronal CT of the orbits is the key view. In a blowout fracture, look for orbital fat or muscle hanging into the maxillary sinus (the "teardrop" sign) and a rounded or trapped inferior rectus. In thyroid eye disease the muscle bellies are enlarged while the tendons are spared. ## 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 - In children a trapdoor floor fracture can grip the muscle with almost no bruising ("white-eyed blowout"); pain on upgaze, nausea, vomiting and a slow heart rate (oculocardiac reflex) make it a surgical emergency - Numbness of the cheek, upper lip and upper teeth after a floor fracture shows injury to the infraorbital nerve - Thyroid eye disease: enlarged muscles push the eye forward (exophthalmos) and can compress the optic nerve at a crowded orbital apex ## Development Arises from the shared head-mesoderm mass of the oculomotor muscles near the optic stalk; congenital fibrosis of the extraocular muscles mainly stiffens this group, often leaving the eyes held down with ptosis. ## Memory aid Muscles enlarged in thyroid eye disease, most to least often: "I'M SLOw" (Inferior, Medial, Superior, Lateral, Obliques). ## Related conditions - [Graves disease (hyperthyroidism)](https://durgical.com/en/conditions/graves-disease/) - [Orbital floor (blowout) fracture](https://durgical.com/en/conditions/orbital-floor-fracture/) - [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. ## Which extraocular muscle is most often trapped in an orbital floor (blowout) fracture, and what is the sign? The inferior rectus: upgaze is limited and the person sees double looking up. ## What is a «white-eyed blowout» in a child, and why is it an emergency? A trapdoor floor fracture gripping the inferior rectus with little bruising; pain on upgaze, nausea and a slow heart rate (oculocardiac reflex) need urgent surgery. ## Which muscle is usually the first and most enlarged in thyroid eye disease? The inferior rectus; when tight it holds the eye down and limits upgaze. ## What does the forced duction test tell in limited upgaze? Resistance to moving the eye up means a mechanical restriction (trapped or fibrotic inferior rectus), not a nerve palsy. ## What does cheek, upper lip and upper teeth numbness after a floor fracture indicate? Injury to the infraorbital nerve, which runs in the orbital floor below the inferior rectus. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/inferior-rectus-muscle/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** musculus rectus inferior TA2 2043 **Official Spanish (DeCS)** Músculo recto inferior DeCS D009801 **English (TA2)** Inferior rectus muscle **Also called** musculus rectus inferior 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 Inferior Rectus Muscle](https://www.ncbi.nlm.nih.gov/books/NBK518978/); [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/inferior-rectus-muscle/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/inferior-rectus-muscle/