RCEM Basic Science Curriculum
Overview of the anatomical arrangement of the muscles: the cone of orbital muscle.
The functions and innervation of each of the following named muscles:
- Superior rectus
- Medial rectus
- Inferior rectus
- Lateral rectus
- Superior oblique
- Inferior oblique
Clinical effects of palsies of the III, IV and VI nerves
- Clinical effects of paralysis of a given extraocular muscle (eg superior rectus => diplopia on looking up)
The movements of the eye are:
- Elevation – moving the pupil superiorly
- Depression – moving the pupil inferiorly
- Abduction – moving the pupil laterally
- Adduction – moving the pupil medially
- Medial rotation (intorsion) – rotating the upper part of the pupil medially (towards the nose)
- Lateral rotation (extorsion) – rotating the upper part of the pupil laterally (towards the temple)
There are six extraocular eye muscles which act to turn or rotate the eye about its vertical, horizontal, and anteroposterior axes:
- The superior rectus acts to produce elevation, adduction and medial rotation of the eyeball.
- The inferior rectus acts to produce depression, adduction and lateral rotation of the eyeball.
- The medial rectus acts to produce adduction of the eyeball.
- The lateral rectus acts to produce abduction of the eyeball.
- The superior oblique acts to produce intorsion (primarily), depression and abduction of the eyeball.
- The inferior oblique acts to produce extorsion (primarily), elevation and abduction of the eyeball.
The recti muscles all originate as a group from a common tendinous ring at the apex of the orbit and form a cone of muscles as they pass forward to their attachment on the eyeball.
To test the muscles in isolation, ask the patient to:
- Superior rectus – look laterally and upwards
- Inferior rectus – look laterally and downwards
- Lateral rectus – look laterally in the horizontal plane
- Medial rectus – look medially in the horizontal plane
- Superior oblique – look medially and downwards
- Inferior oblique – look medially and upwards
Cranial Nerve III Palsy
The oculomotor nerve (CN III) supplies all of the ocular muscles except for the superior oblique and the lateral rectus muscle. It also supplies the levator palpebrae superioris (elevator of the upper eyelid) and provides the parasympathetic supply to the sphincter pupillae (pupillary constriction) and ciliary muscle (accommodation). CN III palsy causes a depressed and abducted eye (down and out pupil), ptosis and pupillary dilatation (with loss of accommodation).
Cranial Nerve IV Palsy
The superior oblique is innervated by the trochlear nerve (CN IV). CN IV palsy causes weakness of downward gaze. The patient complains of difficulty reading or walking downstairs and of vertical diplopia. The eye is extorted and may be elevated, the patient may head tilt to the opposite side of the palsy to compensate.
Cranial Nerve VI Palsy
The lateral rectus is innervated by the abducens nerve (CN VI). CN VI palsy results in a convergent squint at rest (eye turned inwards) and the patient complains of horizontal diplopia when looking towards the affected side. With complete paralysis, the eye cannot abduct past the midline.