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The human eye contains six muscles that work together to control eye movement and vision. These muscles are known as extraocular muscles and are separate from the eyeball itself. They include four rectus muscles (superior, medial, lateral, and inferior) and two oblique muscles (superior and inferior). While the rectus muscles are derived from the Latin word rectus meaning straight, the oblique muscles take an angular approach to the eyeball. Eye muscle conditions can cause eye movement disorders, leading to serious conditions such as strabismus, or eye misalignment, where the eyes appear crossed.
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What You'll Learn
Eye movement disorders
There are two common types of eye movement disorders: strabismus and nystagmus. Strabismus, also known as crossed eyes or walleye, is a disorder in which the two eyes do not line up in the same direction. It can result in double vision. Nystagmus refers to fast, uncontrollable movements of the eyes, sometimes called "dancing eyes". The eyes can make repetitive movements in one direction or back-and-forth movements. This can affect one or both eyes, and the movements can be constant or intermittent. They can be horizontal, vertical, oblique, torsional (circular), or combinations of these.
Other types of eye movement disorders include accommodative esotropia, Brown syndrome, and conjugate gaze palsies. In some cases, eye movement disorders can be a sign of more serious underlying conditions, such as spinal muscular atrophy or Parkinson's disease.
The eyes are controlled by six external muscles that work in pairs. These muscles are responsible for directing the eyes side-to-side, up and down, or at diagonal angles. They are called the rectus muscles and oblique muscles. Each eye has four rectus muscles: superior rectus, inferior rectus, medial rectus, and lateral rectus. Each eye also has two oblique muscles: superior oblique and inferior oblique. These muscles work together to control the movement of the eyes and enable visual capabilities such as depth perception and three-dimensional (3D) vision.
Treatment options for eye movement disorders vary depending on the specific disorder and the patient's needs. They can include glasses, patches, eye muscle exercises, and surgery. In some cases, computer and optical devices are used to correct specific eye movement disorders through visual-motor-skill and endurance exercises. Genetic testing and counselling may also be recommended if hereditary eye movement disorders are suspected.
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Extraocular muscles
The extraocular muscles, also known as extrinsic ocular muscles, are the seven extrinsic muscles of the eye in humans and other animals. Six of these muscles, the four rectus muscles and the superior and inferior oblique muscles, control eye movement. The seventh muscle, the levator palpebrae superioris, controls eyelid elevation.
The four rectus muscles are the superior rectus, lateral rectus, medial rectus, and inferior rectus. They are named according to their relative positions of attachment, with “superior” meaning “up” or “top”, “inferior” meaning “down” or “bottom”, “medial” meaning “middle” or “closer to the nose”, and “lateral” meaning “to the side”. The recti muscles are almost equal in length at around 40 mm, but the lengths of their associated tendons differ.
The two oblique muscles are the superior and inferior obliques. Unlike the recti group of muscles, the oblique muscles do not originate from the common tendinous ring. Instead, they take an angular approach to the eyeball, attaching to the posterior surface of the sclera. The superior oblique muscle originates at the back of the orbit, getting rounder as it courses forward, while the inferior oblique muscle originates at the lower front of the nasal orbital wall, wraps around the bottom of the eye, and attaches just behind the lateral rectus muscle.
The levator palpebrae superioris (LPS) is the only muscle involved in raising the superior eyelid. It is innervated by the oculomotor nerve (CN III) and the superior tarsal muscle, which is located within the LPS, is innervated by the sympathetic nervous system.
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Rectus and oblique muscles
Each eye has six muscles that control its movement. These muscles are how you can direct your eyes side-to-side, up and down, or at diagonal angles. The muscles that control eye movement all attach to the outside of the eyeball, which is why experts sometimes refer to them as "external" or "extrinsic" muscles.
There are two types of eye movement muscles: rectus and oblique. Each eye has four rectus muscles: superior rectus, inferior rectus, medial rectus, and lateral rectus. "Superior" means "top", "inferior" means "bottom", "medial" means "middle" (as in, closer to your nose), and "lateral" means "to the side", like where your ears are.
Each eye also has two oblique muscles: superior oblique and inferior oblique. The superior oblique works like a pulley, starting at the upper back of the eye and extending forward, then threading through a small bony opening on the upper-inner side of the eye socket. The inferior oblique attaches to the lower-inner side of your eye socket, extends laterally (away from your nose), wraps around the bottom of your eye, and attaches just behind the lateral rectus on the far side.
Unlike the rectus muscles, the oblique muscles do not originate from the common tendinous ring. From their origin, the oblique muscles take an angular approach to the eyeball (in contrast to the straight approach of the rectus muscles). They attach to the posterior surface of the sclera.
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Eye misalignment
Strabismus affects vision as both eyes must aim at the same spot together to see. In adults, this typically results in double vision. However, in children, the brain suppresses one of the images to avoid double vision. While this adaptation is beneficial in some ways, it also means that the ignored eye loses the ability to see perfect "20/20" vision, a condition called amblyopia. Young patients with eye misalignment may also experience poor stereo or 3D vision and depth perception.
The causes of eye misalignment vary and are sometimes unknown. Potential causes include high farsightedness, thyroid eye disease, cataracts, eye injuries, myasthenia gravis, cranial nerve palsies, and brain or birth problems. Six muscles control eye movement and are attached to the outside of each eye. Two muscles in each eye move the eye right or left, while the other four muscles move it up or down and control tilting movements. To focus both eyes on a single target, all six eye muscles on each eye must work together with the corresponding muscles of the opposite eye. The brain coordinates these eye muscle movements.
There are two types of eye muscles: rectus muscles and oblique muscles. Each eye has four rectus muscles: superior rectus, inferior rectus, medial rectus, and lateral rectus. Each eye also has two oblique muscles: superior oblique and inferior oblique. The rectus muscles have a direct path from origin to attachment, while the oblique muscles take an angular approach to the eyeball.
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Eye muscle conditions
Muscle Disorders
Muscle disorders can be inherited or develop spontaneously before birth or at some point during a person's life. Examples of muscle disorders that affect eye movement include myotonic dystrophy, oculopharyngeal muscular dystrophy (OPMD), Kearns-Sayre syndrome, thyroid eye disease or Graves' disease, strabismus (eye misalignment), amblyopia (lazy eye), and congenital fibrosis of the extraocular muscles.
Nervous System-Related Disorders
Nervous system-related disorders that affect eye movement include cranial nerve palsies, myasthenia gravis, multiple sclerosis, stroke and transient ischemic attacks (TIAs), tumours and cancers affecting the brain or cranial nerves, nerve or brain lesions, Lyme disease, Parkinson's disease, and parkinsonism. Sixth (abducens) nerve palsy is the most common form of cranial nerve palsy.
Diagnosis and Treatment
Neurological exams and lab tests, such as blood tests, can be used to diagnose eye muscle disorders. Treatments for eye muscle disorders vary widely and may include glasses, patches, eye muscle exercises, and surgery. In some cases, treating the underlying condition may be sufficient to resolve the eye movement issue.
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Frequently asked questions
The human eye has six muscles that control eye movement. These are the four rectus muscles and the two oblique muscles.
The four rectus muscles are the superior rectus, the inferior rectus, the medial rectus, and the lateral rectus. The superior and inferior rectus muscles help elevate and depress the eye, respectively. The medial rectus rotates the eye around the vertical axis, and the lateral rectus rotates it laterally.
The two oblique muscles are the superior oblique and the inferior oblique. The superior oblique abducts, depresses, and medially rotates the eye. The inferior oblique muscle has a similar function but moves the eye upward when looking towards the nose.
