Oculomotor nerve palsy or oculomotor neuropathy is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the

oculomotor nerve The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements of ...

supplies the majority of the muscles controlling eye movements (four of the six extraocular muscles, excluding only the

lateral rectus Lateral is a geometric term of location which may refer to: Healthcare * Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics * Lateral ...

and superior oblique). Damage to this nerve will result in an inability to move the eye normally. The nerve also supplies the upper eyelid muscle (

levator palpebrae superioris The levator palpebrae superioris ( la, elevating muscle of upper eyelid) is the muscle in the orbit that elevates the upper eyelid. Structure The levator palpebrae superioris originates from inferior surface of the lesser wing of the sphenoid bo ...

) and is accompanied by parasympathetic fibers innervating the muscles responsible for pupil constriction ( sphincter pupillae). The limitations of eye movement resulting from the condition are generally so severe that patients are often unable to maintain normal eye alignment when gazing straight ahead, leading to

strabismus Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a ...

and, as a consequence, double vision (

diplopia Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often v ...

Presentation

A complete oculomotor nerve palsy will result in a characteristic displacement outward (

exotropia Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia and usually involves more severe axis deviation than exophoria. People with exotropia often experience crossed diplopia. Intermittent exotrop ...

) and downward (hypotropia). The outward displacement occurs because the

muscle (innervated by the sixth cranial nerve) maintains muscle tone in comparison to the paralyzed medial rectus. The downward displacement occurs because the superior oblique muscle (innervated by the fourth cranial or trochlear nerve) is unantagonized by the paralyzed

superior rectus The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is elevation ...

inferior rectus Inferior may refer to: * Inferiority complex * An anatomical term of location * Inferior angle of the scapula, in the human skeleton * ''Inferior'' (book), by Angela Saini * ''The Inferior'', a 2007 novel by Peadar Ó Guilín See also *Junior (di ...

and

inferior oblique 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 one of the extraocular muscles, and is attached to the maxillary bone (origin) and ...

. The affected individual will also have a ptosis, or drooping of the

eyelid An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eye ...

, and

mydriasis 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 certain types of drugs. Normally, a ...

(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

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. From Greek ἴδιος ''idios'' "one's own" and πάθος ''pathos'' "suffering", ''idiopathy'' means approximately "a disease of its own kin ...

. 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 In genetics, dominance is the phenomenon of one variant ( allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant an ...

inheritance. The condition can also result from

aplasia Aplasia (; from Greek ''a'', "not", "no" + ''plasis'', "formation") is a birth defect where an organ or tissue is wholly or largely absent. It is caused by a defect in a developmental process. Aplastic anemia is the failure of the body to produc ...

hypoplasia Hypoplasia (from Ancient Greek ὑπo- ''hypo-'' 'under' + πλάσις ''plasis'' 'formation'; adjective form ''hypoplastic'') is underdevelopment or incomplete development of a tissue or organ.birth trauma Birth trauma may refer to: * Childbirth-related posttraumatic stress disorder, psychological trauma to the mother following childbirth *Birth trauma (physical) Birth trauma refers to damage of the tissues and organs of a newly delivered child, of ...

Acquired oculomotor palsy

Vascular disorders Vascular disease is a class of diseases of the blood vessels – the arteries and veins of the circulatory system of the body. Vascular disease is a subgroup of cardiovascular disease. Disorders in this vast network of blood vessels can cause a r ...

such as

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

heart disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...

atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no s ...

and

aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus ( ...

, particularly of the

posterior communicating artery In human anatomy, the left and right posterior communicating arteries are arteries at the base of the brain that form part of the circle of Willis. Each posterior communicating artery connects the three cerebral arteries of the same side. Anterio ...

# Space occupying lesions or tumours, both malignant and non-malignant #

Inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...

and

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

Trauma Trauma most often refers to: *Major trauma, in physical medicine, severe physical injury caused by an external source *Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic inju ...

Demyelinating Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be l ...

disease (

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This ...

) #

Autoimmune In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an "autoimmune disease". ...

disorders such as

myasthenia gravis Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, ...

# Post-operatively as a complication of

neurosurgery Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty concerned with the surgical treatment of disorders which affect any portion of the nervous system including the brain, spinal cord and pe ...

Cavernous sinus thrombosis The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica. Structure The ...

Mechanism

As the pair of oculomotor nerves arises from different subnuclei in the

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal ( alertness), and temperature regulation. The name comes from the Greek ''mesos'', ...

, courses through different structures in the brain and branches into superior and inferior divisions after exiting the

cavernous sinus The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica. Structure The cave ...

es, any lesions along its path will produce different pathological features of the third nerve palsy. The parasympathetic aspect of the nerve (which constricts pupils and thicken the lens) is located on the nerve surface, supplied by pial blood vessels. The nerve's core contains the main trunk of the oculomotor nerve, supplied by

vasa vasorum Vasa vasorum are small blood vessels that comprise a vascular network supplying the walls of large blood vessels, such as elastic arteries (e.g., the aorta) and large veins (e.g., the venae cavae). The name derives . Occasionally two differen ...

. Thus pathologies affecting the nerve's core without affecting the superficial part of the nerve (thus sparing the pupillary reflex) are known as "medical" oculomotor nerve palsy. The "surgical" type of oculomotor nerve palsy is caused by external structures compressing on the nerve or trauma, which affects the entire nerve, thus affecting pupillary reflex.

Ischemic stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop funct ...

selectively affects somatic fibers over

parasympathetic 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 ...

fibers, while traumatic stroke affects both types more equally. Ischemic stroke affects the 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 cause ptosis and impaired movement of the eye, pupillary abnormalities are more commonly associated with trauma and the "surgical third" rather than with ischemia (the "medical third"). A posterior communicating artery aneurysm will generally cause compression of the entire third nerve and will this prevent any nerve signal conduction, affecting the somatic system as well as the autonomic. The compression of the external autonomic fibres renders the pupil nonreactive and 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. The sparing of the pupil is thought to be associated with the microfasciculation of the fibers that control the pupillomotor function located on the outmost aspect of the occulomotor nerve fibres; these fibres are spared because they are outermost and therefore less prone to ischemic damage than are the innermost fibres.

References

External links

{{Eye pathology Disorders of ocular muscles, binocular movement, accommodation and refraction Oculomotor nerve