What Is the Medial Rectus?

The rectus medialis, also known as the inner horizontal muscle ^[1] , and the intraocular rectus muscle (adducens oculi muscle), are the strongest and most powerful muscles in the extraocular muscles. This muscle starts from the superior and inferior aponeurosis and optic nerve sheaths inside and below the optic foramen. From the origin of the Zinn's common tendon ring, it traveled along the inner wall of the orbit and attached to the scleral tissue at a distance of 5.5 mm from the inner edge of the cornea. The medial rectus muscle is about 40 mm long and the tendon is about 3.7 to 4.0 mm long. The attachment point is about 1.3 mm wide and the muscle width is 10.3 mm. Above the medial rectus muscle there is the superior oblique muscle, the lower part is the orbital floor, the inner side is orbital fat and ethmoid cardboard, the outer side is orbital fat and the eyeball, innervated by the oculomotor nerve, and its branch 26 mm away from the muscle stop is the innervation point. In the first eye position, this muscle contracts when the muscle contracts. When the line of sight is higher than the horizontal line, it can help the eyeballs turn up, and when the line of sight is lower than the horizontal line, it can help the eyeballs turn down.

The rectus medialis, also known as the inner horizontal muscle ^[1] , and the intraocular rectus muscle (adducens oculi muscle), are the strongest and most powerful muscles in the extraocular muscles. This muscle starts from the superior and inferior aponeurosis and optic nerve sheaths inside and below the optic foramen. From the origin of the Zinn's common tendon ring, it traveled along the inner wall of the orbit and attached to the scleral tissue at a distance of 5.5 mm from the inner edge of the cornea. The medial rectus muscle is about 40 mm long and the tendon is about 3.7 to 4.0 mm long. The attachment point is about 1.3 mm wide and the muscle width is 10.3 mm. Above the medial rectus muscle there is the superior oblique muscle, the lower part is the orbital floor, the inner side is orbital fat and ethmoid cardboard, the outer side is orbital fat and the eyeball, innervated by the oculomotor nerve, and its branch 26 mm away from the muscle stop is the innervation point. In the first eye position, this muscle contracts when the muscle contracts. When the line of sight is higher than the horizontal line, it can help the eyeballs turn up, and when the line of sight is lower than the horizontal line, it can help the eyeballs turn down.

Chinese name

Medial rectus

Foreign name

rectus medialis

location

Located inside the eyeball

Explain

Innervated by oculomotor nerve

Medial rectus clinical disease

1. Medial rectus paralysis:

(1) Cause

Occurrence of oculomotor nerve palsy occurs in about 35% of patients with midbrain infarction, often accompanied by symptoms such as ataxia and sensory disturbances. Among them, the involvement of the medial rectus muscle is most common in ophthalmoplegia, which may be related to the poor tolerance of the medial rectus subnucleus to ischemia and hypoxia. A few patients with midbrain infarction can still see "Plus-minus lid syndrome", i.e., ipsilateral upper eyelid droop, contralateral eyelid contraction, myasthenia gravis, orbital myositis, or oculomotor nerve injury Later patients are more common. The median subnucleus of the oculomotor nucleus has an inhibitory effect on the levator levator muscle, and damage to this nucleus can cause hyperfunction of the levator levator muscle.

(2) Clinical symptoms

After the medial rectus is paralyzed, the lateral rectus muscle has no antagonistic power, so exotropia occurs. The patient's introversion is significantly limited and generally cannot cross the midline. The second oblique angle is larger than the first oblique angle. Newly diagnosed medial rectus paralysis complains of apparent diplopia

And diplopia symptoms such as dizziness and vomiting, the head is biased to the healthy side, and both eyes are looking towards the affected side. In the passive rotation test (Forced ductionetst), there may be some resistance to pulling on the nasal side, and there is no resistance on pulling on the wing.

(3) Differential diagnosis

Internuclear ophthalmoplegia: Caused by medial longitudinal tract lesions between the central pontine and the nucleus of the oculomotor nerve. Unilateral or bilateral involvement. Adduction paralysis on the side of the lesion and abduction nystagmus on the opposite side of the lesion. The asymmetry of nystagmus is that the amplitude of abduction nystagmus is large and the amplitude of adductive nystagmus is small. Spoke function can maintain normal. It is usually caused by embolism or multiple sclerosis of the basilar artery.

Total oculomotor nerve palsy: In addition to the involvement of the medial rectus muscle, the function of the upper and lower rectus muscles, inferior obliques, levator muscles, and pupil sphincter is affected. Droopy upper eyelids and dilated pupils.

Fixed exotropia: Fixed exotropia is also manifested as exotropia and restricted introversion. However, the passive rotation test has a large resistance to inward rotation and often cannot be pulled to the normal position.

Myasthenia gravis: Eye-type myasthenia gravis can affect the medial rectus muscle caused by the introversion. However, myasthenia gravis often causes paralysis of multiple extraocular muscles in both eyes, and is light in the morning and late in the night, and the fatigue test is positive. The neostigmine test can restore eye movement function.

Recessive eye syndrome: Type 1 of recurrent eyeball syndrome manifests as an inability to turn the eyeballs and must be distinguished from the medial rectus paralysis alone. Withdrawal syndrome type I has a characteristic manifestation: the affected eye is accompanied by a small eyelid fissure when it is turned in, the eyeball is receded, and the eyelid fissure is enlarged when it is turned out, which can be upright or with exotropia.