MEDIAL RECTUS

The medial rectus (MR) is a muscle located in the medial aspect of the orbit that is responsible for adduction of the eye. It is one of the extraocular muscles, along with the superior, inferior, and lateral rectus muscles, and the superior and inferior oblique muscles. The MR is innervated by the third cranial nerve (oculomotor nerve) and its actions are mediated by the abducens nerve in the brainstem (Aron & Aron, 2012).

The medial rectus is primarily involved in the adduction of the eye, which is the movement of the eye towards the midline of the body. This action enables the eyes to move across the midline in order to focus on an object. Adduction of the eye is also an important component of ocular convergence, which is the simultaneous movement of both eyes towards the midline in order to maintain binocular vision (Aron & Aron, 2012).

The medial rectus is also involved in intorsion of the eye, which is the movement of the eye inwards towards the nose. This action allows the eyes to rotate inwards in order to view an object from a different angle. Intorsion is important for maintaining binocular vision, as it allows both eyes to rotate inwards in order to maintain stereopsis (Aron & Aron, 2012).

The medial rectus is also involved in the accommodation of the eye, which is the ability of the eye to focus on an object. Accommodation is achieved by the contraction of the ciliary muscle, which is innervated by the oculomotor nerve, and the relaxation of the medial rectus muscle. This action enables the eye to focus on an object by changing the shape of the lens in order to adjust the focal length (Aron & Aron, 2012).

In addition to its role in the eye movements, the medial rectus also plays an important role in ocular motility. Ocular motility is the ability of the eyes to move together in a coordinated fashion, which is necessary for binocular vision. The medial rectus is involved in ocular motility by providing an adducting force that helps to keep the eyes aligned (Aron & Aron, 2012).

Overall, the medial rectus is an important muscle in the orbit that plays an important role in adduction, intorsion, accommodation, and ocular motility.

References

Aron, J. S., & Aron, R. J. (2012). The eye: Basic sciences in practice (4th ed.). Philadelphia, PA: Elsevier.