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# Lateral rectus

The lateral rectus is one of the six muscles that move the eyeball, on its outer side; it turns the eye outward and is supplied by the sixth cranial nerve.

Official name: Lateral rectus muscle

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## What it is

One of the six muscles that move the eyeball, inside the eye socket.

## What it does

Turns the eye outward; supplied by nerve VI.

## Key points

- The only muscle of the abducens nerve (VI): a sixth-nerve palsy leaves the eye turned in (esotropia), unable to abduct, with side-by-side double vision worse at distance and looking toward the weak side
- The abducens nerve has a long intracranial course (up the clivus, over the petrous apex, through the [cavernous sinus](https://durgical.com/en/anatomy/cavernous-sinus/) beside the internal carotid), so raised intracranial pressure can stretch it: a false localising sign
- It arises by two heads that bridge the [superior orbital fissure](https://durgical.com/en/anatomy/superior-orbital-fissure/); what passes between them enters the muscle cone
- The ciliary ganglion lies between it and the optic nerve, near the orbital apex

## 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/) laterally, ~6.9 mm behind the limbus

**Action**
Abduction

**Nerve**
Abducens nerve (VI)

**Blood supply**
[Ophthalmic artery](https://durgical.com/en/anatomy/ophthalmic-artery/) (muscular branches)

## Relations

**Lateral**
Lateral orbital wall ([zygomatic bone](https://durgical.com/en/anatomy/zygomatic-bone/) and greater wing of the sphenoid); at the front, the [lacrimal gland](https://durgical.com/en/anatomy/lacrimal-gland/) above it

**Medial**
Ciliary ganglion and [optic nerve](https://durgical.com/en/anatomy/optic-nerve/); the [abducens nerve](https://durgical.com/en/anatomy/abducens-nerve/) enters its inner (ocular) surface

**Above**
Lacrimal artery and lacrimal nerve running along its upper border to the lacrimal gland

**Below**
Orbital floor; the [inferior oblique](https://durgical.com/en/anatomy/inferior-oblique-muscle/) inserts on the globe beneath its back end

## How to find it

Its tendon inserts about 6.9 mm behind the lateral limbus and is reached through a temporal conjunctival incision. In dissection it follows the lateral orbital wall; at the apex its two heads straddle the superior orbital fissure, and in front the lacrimal gland rests on its tendon.

## Examination

- H-pattern: the person looks straight out to the side; an eye that lags or fails to pass the midline points to the lateral rectus or the abducens nerve (VI)
- Head posture: a person with a sixth-nerve palsy often turns the face toward the weak side to keep single vision

## On imaging

Axial CT or MRI shows it along the lateral orbital wall to the globe; coronal images compare its size with the other recti. In thyroid eye disease it is usually the last rectus to enlarge. In a sixth nerve palsy, imaging targets the nerve's long path: MRI of the brain and skull base (clivus, petrous apex, cavernous sinus), with venography if raised intracranial pressure is suspected.

## 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

- Causes of a sixth-nerve palsy: microvascular disease in adults, raised intracranial pressure, cavernous sinus lesions, tumours of the clivus and petrous apex infection (Gradenigo syndrome); in children, also brainstem tumours
- Inside the cavernous sinus the abducens nerve runs free beside the [internal carotid artery](https://durgical.com/en/anatomy/internal-carotid-artery/), so it is often the first nerve affected by a carotid aneurysm or cavernous sinus thrombosis
- Duane syndrome (congenital): the abducens nucleus is missing and a branch of the [oculomotor nerve](https://durgical.com/en/anatomy/oculomotor-nerve/) reaches the lateral rectus; abduction is limited, and on adduction the globe retracts and the lid opening narrows
- Exotropia (an eye turned out) in children is often intermittent, worse when tired or in bright light; surgery may weaken the lateral rectus

## Development

Develops from head mesoderm near the optic stalk but, unlike its neighbours, is supplied by the abducens nerve; when that nerve fails to form, the muscle can be innervated by the oculomotor nerve instead (the basis of Duane syndrome).

## Memory aid

"LR6 SO4, rest 3": lateral rectus → abducens (VI); [superior oblique](https://durgical.com/en/anatomy/superior-oblique-muscle/) → trochlear (IV); all the others → oculomotor (III).

## Related conditions

- [Strabismus and amblyopia](https://durgical.com/en/conditions/strabismus-and-amblyopia/)
- [Myasthenia gravis](https://durgical.com/en/conditions/myasthenia-gravis/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which nerve supplies the lateral rectus, and what does its palsy cause?

The abducens nerve (VI): the eye turns in and cannot abduct, with side-by-side double vision worse at distance and toward the weak side.

## Why is a sixth-nerve palsy called a false localising sign?

The abducens nerve has a long intracranial course, so raised intracranial pressure can stretch it, wherever the lesion is.

## Why is the abducens nerve often the first affected in cavernous sinus thrombosis or a carotid aneurysm?

It runs free in the cavernous sinus beside the internal carotid artery.

## What is Duane syndrome?

Congenital absence of the abducens nucleus, with an oculomotor branch reaching the lateral rectus: limited abduction, and globe retraction with lid narrowing on adduction.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
musculus rectus lateralis bulbi oculi TA2 2045

**Official Spanish (DeCS)**
Músculo recto lateral DeCS D009801

**English (TA2)**
Lateral rectus muscle

**Also called**
external rectus · musculus rectus termporalis bulbi

## Related

- [Abducens nerve (VI)](https://durgical.com/en/anatomy/abducens-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 Lateral Rectus Muscle](https://www.ncbi.nlm.nih.gov/books/NBK539721/); [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.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/lateral-rectus-muscle/