[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/) › Common tendinous ring [Sense organs](https://durgical.com/en/anatomy/system/sense-organs/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Common tendinous ring The common tendinous ring is a ring of tendon at the back of the eye socket where the four rectus eye muscles start; the optic nerve passes through it. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=common_tendinous_ring&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A ring of tendon at the back of the eye socket. ## What it does The four rectus muscles start here; the optic nerve passes through it. ## Key points - Outside the ring, above it in the superior orbital fissure: the lacrimal, frontal and trochlear nerves and the superior ophthalmic vein; they lie outside the muscle cone - The four recti fan forward from it to form the muscle cone; a retrobulbar (intraconal) block stills the eye, but the [superior oblique](https://durgical.com/en/anatomy/superior-oblique-muscle/) may still move because the [trochlear nerve](https://durgical.com/en/anatomy/trochlear-nerve/) stays outside - The superior and medial recti attach to the optic nerve sheath at the ring, which is why optic neuritis hurts on eye movement - Orbital apex syndrome: optic nerve plus III, IV, V1 and VI: loss of vision with a frozen eye and forehead numbness ## Key facts **Attaches** Around the optic canal and the middle of the superior orbital fissure **Function** Origin of the four recti; II, ophthalmic artery, III, VI and the nasociliary nerve pass through it ## Relations **Contents** [Optic nerve](https://durgical.com/en/anatomy/optic-nerve/) and [ophthalmic artery](https://durgical.com/en/anatomy/ophthalmic-artery/) (from the [optic canal](https://durgical.com/en/anatomy/optic-canal/)); superior and inferior divisions of the [oculomotor nerve (III)](https://durgical.com/en/anatomy/oculomotor-nerve/); nasociliary nerve (V1); [abducens nerve (VI)](https://durgical.com/en/anatomy/abducens-nerve/); usually the sympathetic root of the ciliary ganglion **Above** Above and outside it: the lacrimal, frontal and trochlear nerves and the [superior ophthalmic vein](https://durgical.com/en/anatomy/superior-ophthalmic-vein/); the [levator palpebrae superioris](https://durgical.com/en/anatomy/levator-palpebrae-superioris/) arises just above it **In front** The four recti fanning out around the optic nerve to form the muscle cone, with intraconal fat between them **Behind** Optic canal and [superior orbital fissure](https://durgical.com/en/anatomy/superior-orbital-fissure/), opening into the middle cranial fossa, with the [cavernous sinus](https://durgical.com/en/anatomy/cavernous-sinus/) just behind **Below** The inferior ophthalmic vein, which often passes below the ring ## How to find it In dissection, the orbital roof and the levator are lifted and the four recti traced back to the apex, where they converge on a fibrous ring around the optic canal and the middle part of the superior orbital fissure. ## On imaging Thin-slice MRI with fat suppression and contrast shows the orbital apex and the nearby cavernous sinus: abnormal enhancing tissue suggests inflammation (such as Tolosa–Hunt syndrome), tumour or fungal infection; CT shows fractures and bone erosion of the apex. ## Clinical notes - Causes of orbital apex syndrome: fractures, tumours, inflammation and invasive fungal sinusitis (mucormycosis) in people with poorly controlled diabetes or immunosuppression - Superior orbital fissure syndrome affects III, IV, V1 and VI but spares vision; once the optic nerve is involved it becomes an orbital apex syndrome - Cavernous sinus lesions add the [maxillary nerve](https://durgical.com/en/anatomy/maxillary-nerve/) (V2) and can spread to both sides; comparing these three syndromes localises the lesion - A retrobulbar (intraconal) block places anaesthetic inside the muscle cone that starts at the ring; rare complications are retrobulbar haemorrhage, optic nerve injury and spread along the optic nerve sheath to the brainstem - Swollen recti in thyroid eye disease crowd the apex at the ring and can compress the optic nerve (dysthyroid optic neuropathy), shown by falling colour vision and a relative afferent pupillary defect ## Memory aid Superior orbital fissure from top down: "Live Frankly To See Absolutely No Insult" (Lacrimal, Frontal, Trochlear outside the ring; Superior division of III, Abducens, Nasociliary, Inferior division of III inside it). ## Test yourself Think of the answer, then tap the question to see it. ## Which structures pass through the common tendinous ring? The optic nerve and ophthalmic artery, both divisions of the oculomotor nerve (III), the nasociliary nerve (V1) and the abducens nerve (VI). ## Why may the superior oblique still move after a retrobulbar (intraconal) block? The trochlear nerve passes outside the common tendinous ring, outside the muscle cone. ## Why does optic neuritis hurt on eye movement? The superior and medial recti attach to the optic nerve sheath at the common tendinous ring. ## How does orbital apex syndrome differ from superior orbital fissure syndrome? Both affect III, IV, V1 and VI; orbital apex syndrome also involves the optic nerve, so vision is lost. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/common-tendinous-ring/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** anulus tendineus communis TA2 2047 **Official Spanish (DeCS)** Anillo tendinoso común **English (TA2)** Common tendinous ring **Also called** common anular tendon · anulus of Zinn Sources: Terminologia Anatomica (TA2); [Anatomy, Head and Neck, Eye Extraocular Muscles](https://www.ncbi.nlm.nih.gov/books/NBK519565/); [Anatomy, Head and Neck, Orbit](https://www.ncbi.nlm.nih.gov/books/NBK539843/). ## **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/common-tendinous-ring/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/common-tendinous-ring/