Oculomotor nerve palsy

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Oculomotor nerve palsy
Other namesThird nerve palsy
Eye nerves diagram.svg
Eye nerves diagram
Specialty Ophthalmology, neurology   OOjs UI icon edit-ltr-progressive.svg

Oculomotor nerve palsy is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements (4 out of the 6 extracocular muscles. All except the Lateral Rectus and Superior Oblique). Thus, damage to this nerve will result in the affected individual being unable to move their eye normally. In addition, the nerve also supplies the upper eyelid muscle (levator palpebrae superioris) and It is accompanied by parasympathetic fibers innervating the muscles responsible for pupil constriction (sphincter pupillae) . The limitations of eye movements resulting from the condition are generally so severe that the affected individual is unable to maintain normal alignment of their eyes when looking straight ahead, leading to strabismus and, as a consequence, double vision (diplopia).

Contents

It is also known as "oculomotor neuropathy". [1]

Presentation

A complete oculomotor nerve palsy will result in a characteristic down and out position in the affected eye. The eye will be displaced outward "exotropia" and displaced downward "hypotropia"; outward because the lateral rectus (innervated by the sixth cranial nerve) maintains muscle tone in comparison to the paralyzed medial rectus. The eye will be displaced downward, because the superior oblique (innervated by the fourth cranial or trochlear nerve), is unantagonized by the paralyzed superior rectus, inferior rectus and inferior oblique. The affected individual will also have a ptosis, or drooping of the eyelid, and mydriasis (pupil dilation).

Causes

Oculomotor palsy can arise as a result of a number of different conditions. Non traumatic pupil-sparing oculomotor nerve palsies are often referred to as a 'medical third' with those affecting the pupil being known as a 'surgical third'.

Congenital oculomotor palsy

The origins of the vast majority of congenital oculomotor palsies are unknown, or idiopathic to use the medical term. There is some evidence of a familial tendency to the condition, particularly to a partial palsy involving the superior division of the nerve with an autosomal recessive inheritance. The condition can also result from aplasia or hypoplasia of one or more of the muscles supplied by the oculomotor nerve. It can also occur as a consequence of severe birth trauma.

Acquired oculomotor palsy

  1. Vascular disorders such as diabetes, heart disease, atherosclerosis and aneurysm, particularly of the posterior communicating artery
  2. Space occupying lesions or tumours, both malignant and non-malignant
  3. Inflammation and infection
  4. Trauma
  5. Demyelinating disease (multiple sclerosis)
  6. Autoimmune disorders such as myasthenia gravis
  7. Post-operatively as a complication of neurosurgery
  8. Cavernous sinus thrombosis

Mechanism

Since the pair of oculomotor nerves arises from different subnuclei in the midbrain, courses through different structures in the brain, and branched into superior and inferior divisions after exiting the cavernous sinuses, any lesions along its path will produce different pathological features of the third nerve palsy. Besides, the parasympathetic aspect of the nerve (which constricts pupils and thicken the lens) is located on the nerve surface, supplied by pial blood vessels. Meanwhile, the nerve's core contains the main trunk of the oculomotor nerve, supplied by vasa vasorum. Thus pathologies affecting the nerve's core without affecting the superficial part of the nerve (thus sparing the pupillary reflex) is known as "medical" oculomotor nerve palsy. On the contrary, "surgical" oculomotor nerve palsy is caused by external structures compressing on the nerve or trauma, that affects the entire nerve, thus affecting pupillary reflex. [2]

Ischemic stroke selectively affects somatic fibers over parasympathetic fibers, while traumatic stroke affects both types more equally. Ischemic stroke affects vasoneurium which starts to supply the nerve from outside to inside. As the somatic fibers are located in the inner part of the nerve, these fibres are affected more in the setting of ischemia. A similar mechanism is also accurate for diabetes. Therefore, while almost all forms ('medical third' and 'surgical third') cause ptosis and impaired movement of the eye, pupillary abnormalities are more commonly associated with trauma and the 'surgical third' rather than with ischemia, ie the 'medical third'. To further clarify, classically a posterior communicating artery aneurysm will cause compression of the entire third nerve and so prevent ANY nerve signal conduction thus affecting the somatic system and also the autonomic. The compression of the external autonomic fibres renders the pupil non reactive and thus leads to the surgical third nerve palsy.

Oculomotor palsy can be of acute onset over hours with symptoms of headache when associated with diabetes mellitus. Diabetic neuropathy of the oculomotor nerve in a majority of cases does not affect the pupil. [3] The sparing of the pupil is thought to be associated with the microfasciculation of the fibers which control the pupillomotor function located on the outmost aspect of the occulomotor nerve fibres; these fibres are spared because they are outermost and so less prone to ischaemic damage than the innermost fibres. [4]


Related Research Articles

Cranial nerves Nerves that emerge directly from the brain and the brainstem

Cranial nerves are the nerves that emerge directly from the brain, of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck, including the special senses of vision, taste, smell, and hearing.

Parasympathetic nervous system Division of the autonomic nervous system

The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

Mydriasis is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of drugs.

Abducens nerve

The abducens nerve is the sixth cranial nerve (CNVI), in humans, that controls the movement of the lateral rectus muscle, responsible for outward gaze. It is a somatic efferent nerve.

Facial nerve Seventh cranial nerve

The facial nerve is the seventh cranial nerve, or simply CN VII. It emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue. The nerves typically travels from the pons through the facial canal in the temporal bone and exits the skull at the stylomastoid foramen. It arises from the brainstem from an area posterior to the cranial nerve VI and anterior to cranial nerve VIII.

Oculomotor nerve Third cranial nerve

The oculomotor nerve is the third cranial nerve. It enters the orbit through the superior orbital fissure and innervates extrinsic eye muscles that enable most movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the intrinsic eye muscles that enable pupillary constriction and accommodation. The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement.

Trochlear nerve

The trochlear nerve, also called the fourth cranial nerve or CN IV, is a motor nerve that innervates just one muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea.

Diabetic neuropathy refers to various types of nerve damage associated with diabetes mellitus. Symptoms depend on the site of nerve damage and can include motor changes such as weakness; sensory symptoms such as numbness, tingling, or pain; or autonomic changes such as urinary symptoms. These changes are thought to result from microvascular injury involving small blood vessels that supply nerves. Relatively common conditions which may be associated with diabetic neuropathy include distal symmetric polyneuropathy; third, fourth, or sixth cranial nerve palsy; mononeuropathy; mononeuropathy multiplex; diabetic amyotrophy; and autonomic neuropathy.

Pupillary light reflex

The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness. A greater intensity of light causes the pupil to constrict, whereas a lower intensity of light causes the pupil to dilate. Thus, the pupillary light reflex regulates the intensity of light entering the eye. Light shone into one eye will cause both pupils to constrict.

Accommodation reflex

The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object, comprising coordinated changes in vergence, lens shape (accommodation) and pupil size. It is dependent on cranial nerve II, superior centers (interneuron) and cranial nerve III. The change in the shape of the lens is controlled by ciliary muscles inside the eye. Changes in contraction of the ciliary muscles alters the focal distance of the eye, causing nearer or farther images to come into focus on the retina; this process is known as accommodation. The reflex, controlled by the parasympathetic nervous system, involves three responses: pupil constriction, lens accommodation, and convergence.

Duane syndrome Rare congenital disease characterized by external gaze palsy

Duane syndrome is a congenital rare type of strabismus most commonly characterized by the inability of the eye to move outward. The syndrome was first described by ophthalmologists Jakob Stilling (1887) and Siegmund Türk (1896), and subsequently named after Alexander Duane, who discussed the disorder in more detail in 1905.

Eye movement Movement of the eyes

Eye movement includes the voluntary or involuntary movement of the eyes, helping in acquiring, fixating and tracking visual stimuli. A special type of eye movement, rapid eye movement, occurs during REM sleep.

Lateral rectus muscle

The lateral rectus muscle is a muscle on the lateral side of the eye in the orbit. It is one of six extraocular muscles that control the movements of the eye. The lateral rectus muscle is responsible for lateral movement of the eyeball, specifically abduction. Abduction describes the movement of the eye away from the midline, allowing the eyeball to move horizontally in the lateral direction, bringing the pupil away from the midline of the body.

Inferior oblique muscle Part of the eye

The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is an extraocular muscle, and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion). The inferior oblique is innervated by the inferior branch of the oculomotor nerve.

Ciliary ganglion Bundle of nerve parasympathetic ganglion

The ciliary ganglion is a bundle of nerve parasympathetic ganglion located just behind the eye in the posterior orbit. It is 1–2 mm in diameter and in humans contains approximately 2,500 neurons. The ganglion contains postganglionic parasympathetic neurons. These neurons supply the pupillary sphincter muscle, which constricts the pupil, and the ciliary muscle which contracts to make the lens more convex. Both of these muscles are involuntary since they are controlled by the parasympathetic division of the autonomic nervous system.

Anisocoria Medical condition

Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting up to 20% of the population, anisocoria is often entirely harmless, but can be a sign of more serious medical problems.

Sixth nerve palsy Medical condition

Sixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI, which is responsible for causing contraction of the lateral rectus muscle to abduct the eye. The inability of an eye to turn outward, results in a convergent strabismus or esotropia of which the primary symptom is diplopia in which the two images appear side-by-side. Thus, the diplopia is horizontal and worse in the distance. Diplopia is also increased on looking to the affected side and is partly caused by overaction of the medial rectus on the unaffected side as it tries to provide the extra innervation to the affected lateral rectus. These two muscles are synergists or "yoke muscles" as both attempt to move the eye over to the left or right. The condition is commonly unilateral but can also occur bilaterally.

Ptosis (eyelid) Drooping of the upper eyelid as a medical symptom

Ptosis, also known as blepharoptosis, is a drooping or falling of the upper eyelid. The drooping may be worse after being awake longer when the individual's muscles are tired. This condition is sometimes called "lazy eye", but that term normally refers to the condition amblyopia. If severe enough and left untreated, the drooping eyelid can cause other conditions, such as amblyopia or astigmatism. This is why it is especially important for this disorder to be treated in children at a young age, before it can interfere with vision development.

Synkinesis is a neurological symptom in which a voluntary muscle movement causes the simultaneous involuntary contraction of other muscles. An example might be smiling inducing an involuntary contraction of the eye muscles, causing a person to squint when smiling. Facial and extraocular muscles are affected most often; in rare cases, a person's hands might perform mirror movements.

Roots of the ciliary ganglion

The ciliary ganglion is a parasympathetic ganglion located just behind the eye in the posterior orbit. Three types of axons enter the ciliary ganglion but only the preganglionic parasympathetic axons synapse there. The entering axons are arranged into three roots of the ciliary ganglion, which join enter the posterior surface of the ganglion.

References

  1. ↑ Mohammad, J; Kefah, AH; Abdel, Aziz H (2008). "Oculomotor neuropathy following tetanus toxoid injection". Neurol India. 56 (2): 214–6. doi:10.4103/0028-3886.42013. PMID   18688160.
  2. ↑ Marais, W.; Barrett, S. (2013-03-30). "An overview of the third, fourth and sixth cranial nerve palsies". Continuing Medical Education. 31 (4): 147–152. ISSN   2078-5143.
  3. ↑ Goldstein, JE (1960). "Diabetic ophthalmopegia with special reference to the pupil". Arch Ophthalmol. 64: 592. doi:10.1001/archopht.1960.01840010594018.
  4. ↑ Dyck; Thomas (1999). Diabetic Neuropathy. pp. 458–459.
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