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Overview of Neuro-ophthalmologic and Cranial Nerve Disorders

by Michael Rubin, MDCM

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.

Cranial nerves.

Cranial Nerves

Nerve

Function

Possible 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

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 (called disk at risk)

Complications after cataract extraction

Connective tissue disease that causes arteritis (eg, temporal arteritis, antiphospholipid antibody syndrome)

Diabetes

Hypotension or hypovolemia if severe

Ipsilateral internal carotid artery obstruction

Phosphodiesterase type 5 (PDE5) inhibitors (eg, sildenafil, tadalafil, vardenafil)

Retinal artery embolism

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)

Drugs (chloramphenicol, ethambutol, isoniazid, streptomycin, sulfonamides, digitalis, chlorpropamide, ergot, disulfiram)

Methanol ingestion

Nutritional deprivation if severe

Organic mercury

Vitamin B 12 deficiency

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 its fascicle in the midbrain

Transtentorial herniation due to intracranial mass (eg, subdural hematoma, tumor, abscess)

Trochlear (4th)

Moves eye in and down via the superior oblique muscle

Palsies

Often idiopathic

Head trauma

Infarction often due to small-vessel disease (eg, in diabetes)

Tentorial meningioma

Pinealoma

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)

  • Ophthalmic division

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

  • Maxillary and mandibular divisions

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

Palsies

Often idiopathic

Head trauma

Increased intracranial pressure

Infarction (may be mononeuritis multiplex)

Infections or tumors affecting the meninges

Multiple sclerosis

Nasopharyngeal carcinoma

Pontine or cerebellar tumors

Pontine infarction

Wernicke encephalopathy

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

Bell palsy

Guillain-Barré syndrome

Infarcts and tumors of the pons

Lyme disease

Melkersson-Rosenthal syndrome

Ramsay Hunt syndrome

Sarcoidosis

Tumors that invade the temporal bone

Uveoparotid fever (Heerfordt syndrome)

Hemifacial spasm

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

Meniere disease

Barotrauma

Benign paroxysmal positional vertigo

Otolithic aggregation in the posterior or horizontal semicircular canal, related to aging and/or trauma

Infection (occasionally)

Vestibular neuronitis

Viral infection

Hearing loss or disturbance

Acoustic neuromas

Aging

Barotrauma

Cerebellopontine angle tumors

Congenital rubella infection

Exposure to loud noises

Hereditary disorders

Meningitis

Viral infection (possibly)

Glossopharyngeal (9th)

Provides sensory input from the pharynx, tonsils, posterior tongue, and carotid arteries

Glossopharyngeal neuralgia

Ectatic artery or tumor (less common) compressing the nerve

Moves muscles of swallowing and salivary glands

Helps regulate BP

Glossopharyngeal neuropathy

Tumor or aneurysm in the posterior fossa or jugular foramen

Vagus (10th)

Moves vocal cords and muscles for swallowing

Transmits impulses to the heart and smooth muscles of visceral organs

Hoarseness, dysphonia, and dysphagia

Vasovagal syncope

Entrapment of recurrent laryngeal nerve by mediastinal tumor

Herpes zoster

Infectious or carcinomatous meningitis

Medullary tumors or ischemia (eg, lateral medullary syndrome)

Accessory (11th)

Turns the head

Shrugs the shoulders

Partial or complete paralysis of the sternocleidomastoid and trapezius

Iatrogenic (eg, due to lymph node biopsy in posterior triangle of the neck)

Idiopathic

Trauma

Tumors at the skull base or near the meninges

Hypoglossal (12th)

Moves the tongue

Atrophy and fasciculation of tongue

Intramedullary lesions (eg, motor neuron disease, 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 cranial nerves. Amyotrophic lateral sclerosis may cause prominent tongue fasciculations.

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

Evaluation includes the following:

Visual system examination includes ophthalmoscopy and testing of visual acuity, visual fields (see Table: Visual field testing), pupils (see Table: Common Pupillary Abnormalities), and eye movements (ocular motility—see Table: Common Disturbances of Ocular Motility). As part of this testing, the 2nd, 3rd, 4th, and 6th cranial nerves are examined (see also Cranial nerves). 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 sec) 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

Organophosphate or cholinergic toxins

Bilateral dilation with preserved light reflexes

Hyperadrenergic states (eg, withdrawal syndromes, drugs such as sympathomimetics or cocaine, thyrotoxicosis)

Bilateral dilation with impaired direct light response

Mydriatic eye drops such as sympathomimetics (eg, phenylephrine) and cycloplegics (eg, cyclopentolate, tropicamide, homatropine, atropine)

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

*Transtentorial herniation and use of mydriatic eye drops can often be distinguished by instilling a drop of pilocarpine ocular solution into the dilated pupil; no constriction in response suggests mydriatic eye drops.

Tonic 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 (see Diplopia). If diplopia disappears when either eye is closed (binocular diplopia), the cause is probably a disorder of ocular motility. The 2 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 (see also Symptoms of Ophthalmologic Disorders:Physical examination).

Common Disturbances of Ocular Motility

Clinical Finding

Syndrome

Common Causes

Pareses

Paresis of horizontal gaze in one direction

Conjugate horizontal gaze palsy

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

Wernicke encephalopathy

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

One-and-a-half syndrome

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

Internuclear ophthalmoplegia

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

Conjugate downward gaze palsy

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

3rd cranial nerve palsy

Aneurysms

Oculomotor nerve or midbrain ischemia

Trauma

Transtentorial herniation

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)

4th cranial nerve palsy

Idiopathic

Head trauma

Ischemia

Congenital

Unilateral paresis of eye abduction

6th cranial nerve palsy

Idiopathic

Infarct

Vasculitis

Increased intracranial pressure

Wernicke encephalopathy

Multiple sclerosis

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:

  • Myasthenia gravis

  • Graves disease

  • Botulism

  • Mitochondrial myopathies (eg, Kearn-Sayre syndrome)

  • Oculopharyngeal dystrophy

  • Myotonic dystrophy

  • Orbital pseudotumor

Involuntary or abnormal movements

Rhythmic involuntary movements, usually bilateral

Nystagmus

see Nystagmus

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:

  • Postanoxic encephalopathy

  • Occult neuroblastoma

  • Paraneoplastic effects

  • Ataxia-telangiectasia

  • Viral encephalitis

  • Toxic effects of drugs

Rapid, conjugate, multidirectional, chaotic movements, often with widespread myoclonus

Opsoclonus

Many causes (same as for ocular flutter, above)

Treatment

Treatment of neuro-ophthalmologic and cranial disorders depends on the cause.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • CIALIS
  • DIABINESE
  • VIAGRA
  • LANIAZID
  • No US brand name
  • ANTABUSE
  • LEVITRA
  • MYAMBUTOL
  • ATROPEN
  • MYDRIACYL, TROPICACYL
  • TUSSIGON
  • ISOPTO CARPINE, PILOPINE HS, SALAGEN
  • AKPENTOLATE, CYCLOGYL

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