Dysfunction of certain cranial nerves may affect the eye, pupil, optic nerve, or extraocular muscles and their nerves; thus, they can be considered cranial nerve disorders, neuro-ophthalmologic disorders, or both.
Neuro-ophthalmologic disorders may also involve dysfunction of the central pathways that control and integrate ocular movement and vision.
Cranial nerve disorders can also involve dysfunction of smell, vision, chewing, facial sensation or expression, taste, hearing, balance, swallowing, phonation, head turning and shoulder elevation, or tongue movements (see table Cranial Nerves). One or more cranial nerves may be affected.
(See also Horner Syndrome, Optic Nerve Disorders, and Approach to the Neurologic Patient.)
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Cranial Nerves
Nerve | Function | Possible Abnormal Findings | Possible Causes*,† |
|---|---|---|---|
Olfactory (1st) | Provides sensory input for smell | Anosmia | Head trauma Nasal disorders (eg, allergic rhinitis) Neurodegenerative disorders (eg, Alzheimer disease, Parkinson disease) Paranasal sinusitis Tumors of the cranial fossa, nasal cavity, and paranasal sinuses Viral infections (eg, COVID-19 due to severe acute respiratory syndrome coronavirus 2 [SARS-CoV2]) |
Optic (2nd) | Provides sensory input for vision | Amaurosis fugax (transient monocular blindness), unilateral loss of superior or inferior visual field | Embolism of the ophthalmic artery Ipsilateral internal carotid disease Embolism of retinal arteries |
Anterior ischemic optic neuropathy | Crowded optic disk morphology (with a small-cup-to-disk ratio, called disk at risk) Complications after cataract extraction Connective tissue disease that causes arteritis (eg, giant cell [temporal] arteritis, antiphospholipid antibody syndrome) Hypotension or hypovolemia if severe Ipsilateral internal carotid artery obstruction | ||
Optic neuritis (papillitis and retrobulbar) | Acute demyelinating disease (eg, multiple sclerosis, neuromyelitis optica) Bacterial infections (eg, TB, syphilis, Lyme disease) Postinfectious or disseminated encephalomyelitis Uveitis Viral infections (eg, HIV, herpes simplex, hepatitis B, cytomegalovirus) | ||
Toxic-nutritional optic neuropathy (toxic amblyopia) | Methanol ingestion Nutritional deprivation if severe Organic mercury Vitamin B12 deficiency | ||
Hereditary optic neuropathies | |||
Bitemporal hemianopia | Craniopharyngioma Meningioma of tuberculum sellae Saccular aneurysm in the cavernous sinus Suprasellar extension of pituitary adenoma | ||
Oculomotor (3rd) | Raises eyelids Moves eyes up, down, and medially Adjusts amount of light entering eyes Focuses lenses | Palsies | Aneurysm of posterior communicating artery Ischemia of the 3rd cranial nerve (often due to small-vessel disease as occurs in diabetes or hypertension) or its fascicle in the midbrain Transtentorial herniation due to intracranial mass (eg, subdural hematoma, tumor, abscess) Trauma |
Trochlear (4th) | Moves eye in and down via the superior oblique muscle | Palsies | Often idiopathic Infarction often due to small-vessel disease (eg, in diabetes) Tentorial meningioma Pinealoma |
Para | Myokymia of the superior oblique muscle (typically with brief episodic ocular movements that cause subjective visual shimmering, ocular trembling, and/or tilted vision) | Entrapment of the trochlear nerve by a vascular loop (similar to the pathophysiology of trigeminal neuralgia) | |
Trigeminal (5th) | |||
| Provides sensory input from the eye surface, tear glands, scalp, forehead, and upper eyelids | Neuralgia | Vascular loop compressing the nerve root Multiple sclerosis (occasionally) Lesions of cavernous sinus or superior orbital fissure |
| Provides sensory input from the teeth, gums, lip, lining of palate, and skin of the face | Neuralgia | Lesions of cavernous sinus or superior orbital fissure Multiple sclerosis (occasionally) Vascular loop compressing the nerve root |
Moves masticatory muscles (chewing, grinding the teeth) | Neuropathy | Carcinomatous or lymphomatous meningitis Connective tissue disorders Meningiomas, schwannomas, or metastatic tumors at the skull base | |
Abducens (6th) | Moves the eye outward (abduction) via the lateral rectus muscle | Often idiopathic Increased intracranial pressure Infarction (may be mononeuritis multiplex) Infections or tumors affecting the meninges Nasopharyngeal carcinoma Pontine or cerebellar tumors Pontine infarction | |
Facial (7th) | Moves muscles of facial expression Proximal branches: Innervate tear glands and salivary glands and provide sensory input for taste on the anterior two thirds of the tongue | Palsies | Vestibular schwannoma Basilar skull fracture Infarcts and tumors of the pons Melkersson-Rosenthal syndrome Mobius syndrome Ramsay Hunt syndrome (herpes zoster oticus) Tumors that invade the temporal bone Uveoparotid fever (Heerfordt syndrome) |
Artery loop compressing the nerve root | |||
Vestibulocochlear (8th) | Provides sensory input for equilibrium and hearing | Tinnitus, vertigo, sense of fullness in the ear, and hearing loss | |
Otolithic aggregation in the posterior or horizontal semicircular canal, related to aging and/or trauma Infection (occasionally) | |||
Viral infection | |||
Hearing loss or disturbance | Aging Barotrauma Cerebellopontine angle tumors Exposure to loud noises Hereditary disorders Meningitis Viral infection (possibly) Ototoxic drugs (eg, aminoglycosides) | ||
Glossopharyngeal (9th) | Provides sensory input from the pharynx, tonsils, posterior tongue, and carotid arteries | Ectatic artery or tumor (less common) compressing the nerve | |
Moves muscles of swallowing and controls parotid gland secretion Helps regulate BP | Glossopharyngeal neuropathy | Tumor or aneurysm in the posterior fossa or jugular foramen (jugular foramen syndrome) | |
Vagus (10th) | Moves vocal cords and muscles for swallowing Transmits impulses to the heart (slows the heart rate) and smooth muscles of visceral organs (regulates peristalsis) | Hoarseness, dysphonia, and dysphagia Vasovagal syncope | Entrapment of recurrent laryngeal nerve by mediastinal tumor Infectious or carcinomatous meningitis Medullary tumors or ischemia (eg, lateral medullary syndrome) Tumor or aneurysm in the posterior fossa or jugular foramen (jugular foramen syndrome) |
Accessory (11th) | Turns the head Shrugs the shoulders | Partial or complete paralysis of the sternocleidomastoid and upper trapezius muscles | Iatrogenic (eg, due to lymph node biopsy in posterior triangle of the neck) Idiopathic Trauma Tumor or aneurysm in the posterior fossa or jugular foramen (jugular foramen syndrome) |
Hypoglossal (12th) | Moves the tongue | Atrophy and fasciculation of tongue | Intramedullary lesions (eg, tumors) Lesions of the basal meninges or occipital bones (eg, platybasia, Paget disease of skull base) Surgical trauma (eg, due to endarterectomy) Motor neuron disease (eg, amyotrophic lateral sclerosis) |
* Disorders that cause diffuse motor paralysis (eg, myasthenia gravis, botulism, variant Guillain-Barré syndrome, poliomyelitis with bulbar involvement) often affect the motor part of the cranial nerves. | |||
† Hypertension (microvascular disease), diabetes, and infections can cause individual cranial nerve palsies. | |||
Causes and symptoms of neuro-ophthalmologic and cranial nerve disorders overlap. Both types of disorders can result from tumors, inflammation, trauma, systemic disorders, and degenerative or other processes, causing such symptoms as vision loss, diplopia, ptosis, pupillary abnormalities, periocular pain, facial pain, or headache.
Diagnosis of Neuro-ophthalmologic and Cranial Nerve Disorders
Clinical evaluation
Neuroimaging
(See also How to Assess the Cranial Nerves.)
Evaluation of neuro-ophthalmologic and cranial nerve disorders includes the following:
Detailed questioning about symptoms
Tests to detect nystagmus
Visual system examination includes ophthalmoscopy and testing of visual acuity, visual fields, pupils, and eye movements (ocular motility). As part of this testing, the 2nd, 3rd, 4th, and 6th cranial nerves are examined. Neuroimaging with CT or MRI is also usually required.
The following parts of the visual examination are of particular interest in diagnosing neuro-ophthalmologic and cranial nerve disorders.
Pupils are inspected for size, equality, and regularity. Normally, the pupils constrict promptly (within 1 second) and equally during accommodation and during exposure to direct light and to light directed at the other pupil (consensual light reflex). Testing pupillary response to consensual light via a swinging flashlight test can determine whether a defect is present. Normally, the degree of pupillary constriction does not change as the flashlight is swung from eye to eye.
If a relative afferent defect (deafferented pupil, afferent pupillary defect, or Marcus Gunn pupil) is present, the pupil paradoxically dilates when the flashlight swings to the side of the defect. A deafferented pupil constricts in response to consensual but not to direct light.
If an efferent defect is present, the pupil responds sluggishly or does not respond to both direct and consensual light.
Common Pupillary Abnormalities
Finding | Explanation |
|---|---|
Asymmetry of 1–2 mm between pupils, preserved light responses, and no symptoms | Normal variant (physiologic anisocoria) |
Asymmetry, impaired light responses, and preserved response to accommodation (light-near dissociation or Argyll Robertson pupil) | Neurosyphilis (possibly) |
Bilateral constriction | Opioids Miotic eye drops for glaucoma (most common; causing unilateral constriction if single eye is dosed) Pontine hemorrhage (damaging the central sympathetic pathways that dilate pupils) Organophosphate or cholinergic toxins |
Bilateral dilation with preserved light reflexes | |
Bilateral dilation with impaired direct light response | Brain herniation Hypoxic or ischemic encephalopathy |
Unilateral dilation with afferent pupillary defect | Lesions of the eye, retina, or 2nd cranial (optic) nerve |
Unilateral dilation with efferent pupillary defect | Third cranial (oculomotor) nerve palsies, often due to compression (eg, due to aneurysm of the posterior communicating artery or to transtentorial herniation) Iris trauma (also irregular pupil) Mydriatic eye drops* |
Unilateral dilation with minimal or slow direct and consensual light reflexes and pupil constriction in response to accommodation | Tonic (Adie) pupil† |
† Tonic (Adie) pupil is permanent but nonprogressive abnormal dilation of the pupil due to damage of the ciliary ganglion. It typically occurs in women aged 20 to 40. Onset is usually sudden. The only findings are slight blurring of vision, impaired dark adaptation, and sometimes absent deep tendon reflexes. | |
Eye movements are checked by having the patient hold the head steady while tracking the examiner’s finger as it moves to the far right, left, upward, downward, diagonally to either side, and inward toward the patient’s nose (to assess accommodation). However, such examination may miss mild paresis of ocular movement sufficient to cause diplopia.
Diplopia may indicate a defect in bilateral coordination of eye movements (eg, in neural pathways) or in the 3rd (oculomotor), 4th (trochlear), or 6th (abducens) cranial nerve. If diplopia persists when one eye is closed (monocular diplopia), the cause is probably a nonneurologic eye disorder. If diplopia disappears when either eye is closed (binocular diplopia), the cause is probably a disorder of ocular motility. The two images are furthest apart when the patient looks in the direction served by the paretic eye muscle (eg, to the left when the left lateral rectus muscle is paretic). The eye that, when closed, eliminates the more peripheral image is paretic. Placing a red glass over one eye can help identify the paretic eye. When the red glass covers the paretic eye, the more peripheral image is red.
Common Disturbances of Ocular Motility
Clinical Finding | Syndrome | Common Causes |
|---|---|---|
Pareses | ||
Paresis of horizontal gaze in one direction | Lesion in the ipsilateral pontine horizontal gaze center or in the contralateral frontal cortex | |
Paresis of horizontal gaze in both directions | Complete (bilateral) horizontal gaze palsy | Large bilateral pontine lesion affecting both horizontal gaze centers |
Bilateral paresis of all horizontal eye movements except for abduction of the eye contralateral to the lesion; convergence unaffected | Lesion in the medial longitudinal fasciculus and ipsilateral pontine horizontal gaze center | |
Unilateral or bilateral paresis of eye adduction in horizontal lateral gaze but not in convergence | Lesion in the medial longitudinal fasciculus | |
Bilateral paresis of upward eye movement with dilated pupils, loss of the pupillary light response despite preservation of pupillary accommodation and constriction with convergence, downward gaze preference, and downbeating nystagmus | Parinaud syndrome (a type of conjugate vertical gaze palsy) | Pineal tumor Dorsal midbrain infarct |
Bilateral paresis of downward eye movements | Progressive supranuclear palsy | |
Unilateral eye deviation (resting position is down and out); unilateral paresis of eye adduction, elevation, and depression; ptosis; and often a dilated pupil | Aneurysms Oculomotor nerve or midbrain microvascular disease (diabetes and hypertension) Trauma | |
Unilateral paresis of downward and inward (nasal) eye movement, which may be subtle, causing symptoms (difficulty looking down and inward) Head tilt sign (patient tilts the head to the side opposite the affected eye) | Idiopathic Head trauma Ischemia Congenital | |
Unilateral paresis of eye abduction | Idiopathic Increased intracranial pressure Microvascular disease secondary to diabetes or hypertension Trauma | |
Skew deviation (vertical misalignment of the eyes) | Partial and unequal involvement of 3rd cranial nerve nuclei, vertical gaze center, or median longitudinal fasciculus | Brain stem lesion anywhere from midbrain to medulla |
Weakness or restriction of all extraocular muscles | External ophthalmoplegia | Dysfunction of eye muscles or of neuromuscular junction Usually caused by the following:
|
Involuntary or abnormal movements | ||
Rhythmic involuntary movements, usually bilateral | Many causes:
| |
Fast downward jerk and slow upward return to midposition | Ocular bobbing | Extensive pontine destruction or dysfunction |
Gaze overshoot followed by several oscillations | Ocular dysmetria | Cerebellar pathway disorders |
Burst of rapid horizontal oscillations about a point of fixation | Ocular flutter | Many causes:
|
Rapid, conjugate, multidirectional, chaotic movements, often with widespread myoclonus | Opsoclonus | Many causes (same as for ocular flutter, above) |
Treatment of Neuro-ophthalmologic and Cranial Nerve Disorders
Treatment of the cause
Treatment of neuro-ophthalmologic and cranial disorders depends on the cause.
