There are six extrinsic eye muscles that control the movement of each eyeball. These six muscles work together to move your eyes up, down, left, right, and in rotational directions. A seventh muscle, the levator palpebrae superioris, is sometimes grouped with them because it sits in the same region, but it opens your eyelid rather than moving the eyeball itself.
The Six Muscles and What They Do
The six extrinsic (also called extraocular) muscles divide into two groups: four rectus muscles and two oblique muscles. The four rectus muscles are the superior rectus (moves the eye upward), the inferior rectus (moves the eye downward), the medial rectus (turns the eye inward toward the nose), and the lateral rectus (turns the eye outward). The two oblique muscles are the superior oblique, which rotates the eye and helps you look downward and outward, and the inferior oblique, which rotates the eye in the opposite direction and assists with looking upward and outward.
Most of these muscles share a common starting point: a funnel-shaped ring of connective tissue at the back of the eye socket called the annulus of Zinn. All four rectus muscles originate from this ring. The superior oblique starts just above and to the middle of it. The inferior oblique is the exception. It originates from a small depression in the bone near the front of the eye socket, close to the tear duct.
Three Cranial Nerves Control All Six
Your brain controls these muscles through three cranial nerves, each handling a different set. The oculomotor nerve (cranial nerve III) does most of the heavy lifting, controlling the superior rectus, inferior rectus, medial rectus, and inferior oblique. That’s four of the six. The trochlear nerve (cranial nerve IV) controls only the superior oblique. The abducens nerve (cranial nerve VI) controls only the lateral rectus.
A helpful mnemonic some students use is “SO4 LR6”: the Superior Oblique is innervated by cranial nerve 4, the Lateral Rectus by cranial nerve 6, and everything else by cranial nerve 3.
How the Muscles Work Together
No single muscle works in isolation during normal eye movement. Looking to the right, for example, requires your right lateral rectus and your left medial rectus to contract simultaneously while opposing muscles relax. All six muscles in each eye are constantly adjusting tension to keep both eyes pointed at the same target. This coordination is largely managed by your brain rather than the muscles themselves.
Each muscle also has more than one action. The superior rectus primarily elevates the eye, but it also rotates it slightly inward and toward the nose. The oblique muscles are especially complex, combining vertical movement with rotation. This layered control is what lets your eyes track a moving object smoothly or shift focus across a room in a fraction of a second.
How Doctors Test These Muscles
An eye doctor can evaluate all six muscles using a simple test called the H-test. You follow a finger, light, or small object as it traces an H-shaped pattern in front of your face while keeping your head still. Each of the six positions at the corners and ends of the H isolates one specific muscle. For instance, looking up and to the right primarily tests the superior rectus of the right eye, while looking down and to the left isolates the superior oblique of the left eye. If one muscle is weak or restricted, the affected eye will lag behind or fail to reach the expected position.
What Happens When These Muscles Don’t Work Properly
When the six extrinsic muscles can’t keep both eyes aligned, the result is strabismus, commonly known as crossed eyes or wall eyes. In esotropia, one eye turns inward. In exotropia, it drifts outward. Most cases stem from a problem with the brain’s neuromuscular control of eye movement rather than a defect in the muscles themselves.
One common form, accommodative esotropia, occurs alongside uncorrected farsightedness. The extra focusing effort needed to see clearly causes the eyes to turn inward. Intermittent exotropia is another type where one eye drifts outward only some of the time, often when a person is tired or looking at distant objects.
Treatment depends on the cause and severity. Corrective lenses can resolve alignment problems tied to focusing errors. In some cases, injections can weaken an overactive muscle to restore balance. Strabismus surgery adjusts the length or position of one or more of the six muscles to bring the eyes back into alignment.
Why the Levator Palpebrae Superioris Causes Confusion
Some anatomy textbooks list seven extraocular muscles because they include the levator palpebrae superioris, which lifts the upper eyelid. It sits in the same orbital space and shares the same nerve supply (cranial nerve III) as several of the eye-moving muscles. However, because it acts on the eyelid and not the eyeball, most sources distinguish it from the six muscles responsible for eye movement. If an exam or textbook asks how many extrinsic muscles move the eye, the answer is six.