The extraocular muscles are located within the orbit, and provide crucial functions in relation to the movement of the eyeball and superior eyelid. Separate from the eyeball itself, these extrinsic muscles are divided into seven components - the levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique and superior oblique. Functionally, these muscles can be further separated into two groups - those responsible for eye movement (recti and oblique muscles), and those responsible for superior eyelid movement (levator palpebrae superioris). In this article, we will discuss the anatomy of these extraocular muscles, including their attachments, innervation, and actions.
The levator palpebrae superioris (LPS) is the only muscle involved in raising the superior eyelid. A small portion of this muscle contains a collection of smooth muscle fibres, known as the superior tarsal muscle, and is unique in that is is innervated by the sympathetic nervous system. This muscle originates from the lesser wing of the sphenoid bone, immediately above the optic foramen. Its action is to elevate the upper eyelid, and is innervated by the oculomotor nerve (CN III).
There are six muscles involved in the control of the eyeball itself - the four recti muscles, and the two oblique muscles. These muscles originate from the common tendinous ring, a ring of fibrous tissue which surrounds the optic canal at the back of the orbit. All four of the recti muscles have a direct path from origin to attachment, and the name recti is derived from the Latin for 'straight', representing this straight approach.
The four recti muscles are the superior rectus, inferior rectus, medial rectus and lateral rectus. They all originate from the common tendinous ring, and attach to the sclera of the eyeball.
The two oblique muscles are the superior and inferior obliques. Unlike the recti group of muscles, they do not originate from the common tendinous ring. Instead, they take an angular approach to the eyeball, with an attachment to the posterior surface of the sclera.
The extraocular muscles provide essential functions in relation to the movement of the eyeball and superior eyelid. Through their attachments, innervation, and actions, these muscles act together to create the range of eye movement and eyelid elevation necessary for us to carry out daily activities. Understanding the anatomy of these muscles is instrumental in diagnosing and treating any issues related to them.
The levator palpebrae superioris (LPS) is a singular muscle and its role is to raise the superior eyelid. Within the muscle, there is a collection of smooth muscle fibres, known as the superior tarsal muscle, which is innervated by the sympathetic nervous system. The origination of the LPS is from the lesser wing of the sphenoid bone, located immediately above the optic foramen. From here, the muscle connects to the superior tarsal plate of the upper eyelid, a portion of the thick plate of connective tissue. The LPS has one purpose: to elevate the upper eyelid. This is innervated via the oculomotor nerve (CN III).
There are six muscles involved in the control of eyeball movement, which can be divided into two groups. These are the four recti muscles, and the two oblique muscles. The recti muscles all originate from the common tendinous ring, with a direct path from origin to attachment, whereas the oblique muscles have an angular approach to the eyeball.
The two oblique muscles are the superior and inferior obliques and, unlike the recti group of muscles, they 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 recti muscles). They attach to the posterior surface of the sclera.
The extraocular muscles are categorised into four groups - recti muscles, which attach to the lateral and medial aspects of the globe, and the superior and inferior obliques which attach to the globes at the posterior and lateral aspect of the globe. The levator palpebrae superioris attaches to the superior aspect of the tarsal plate of the upper eyelid and is responsible for elevation of the eyelid. Clinical relevance of the extraocular muscles includes conditions such as cranial nerve palsies, which can cause disruption of innervation resulting in weaknesses of eye movements. Horner’s syndrome is one example of an oculomotor cranial nerve palsy caused by disruption of sympathetic innervation to the eye and is characterised by ptosis (drooping eyelid), miosis (pupil constriction) and anhidrosis (absence of sweat glands in the affected area).
Extraocular muscle disorders can be difficult to diagnose and treatment options may vary greatly. In order to gain an accurate diagnosis, a detailed medical history and physical examination will be conducted by a healthcare professional. Imaging studies may also be required to assist with diagnosis and to determine the extent of the condition. Once a diagnosis is made, a combination of medication, lifestyle changes and physical therapy may be recommended in order to control symptoms and improve the functioning of the muscles.
The importance of the extraocular muscles should not be underestimated. These muscles are responsible for the coordination of movement and visual input and they are integral to providing clear and accurate visual information. Eye muscles may be affected by a variety of medical conditions, from injury to neurological disorders, so it is important to pay attention to any changes in the function or sensation of the eyes and seek medical advice where necessary.
