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 1: Neuro-ophthalmologic and Cranial Nerve Disorders: Cranial Nerves). One or more cranial nerves may be affected.
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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.
Evaluation includes the following:
Detailed questioning about symptoms
Examination of the visual system (see also Symptoms of Ophthalmologic Disorders)
Tests to detect nystagmus (see Sidebar 1: Approach to the Patient With Ear Problems: Nystagmus)
Examination of the cranial nerves (see Approach to the Neurologic Patient: Cranial nerves)
Visual system examination includes ophthalmoscopy and testing of visual acuity, visual fields (see Table: Approach to the Ophthalmologic Patient: Visual field testing), pupils (see Table 2: Neuro-ophthalmologic and Cranial Nerve Disorders: Common Pupillary Abnormalities), and eye movements (ocular motility—see Table 3: Neuro-ophthalmologic and Cranial Nerve Disorders: Common Disturbances of Ocular Motility). As part of this testing, the 2nd, 3rd, 4th, and 6th cranial nerves are examined (see also Approach to the Neurologic Patient: 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
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)
Miotic eye drops for glaucoma (most common; causing unilateral constriction if single eye is dosed)
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 light response
Mydriatic eye drops such as sympathomimetics (eg, phenylephrine
and cycloplegics (eg, cyclopentolate
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 Symptoms of Ophthalmologic Disorders: 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
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
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)
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
Oculomotor nerve or midbrain ischemia
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
Unilateral paresis of eye abduction
6th cranial nerve palsy
Increased intracranial pressure
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
Dysfunction of eye muscles or of neuromuscular junction
Usually caused by the following:
Mitochondrial myopathies (eg, Kearn-Sayre syndrome)
Involuntary or abnormal movements
Rhythmic involuntary movements, usually bilateral
see Sidebar 1: Approach to the Patient With Ear Problems: Nystagmus
Fast downward jerk and slow upward return to midposition
Extensive pontine destruction or dysfunction
Gaze overshoot followed by several oscillations
Cerebellar pathway disorders
Burst of rapid horizontal oscillations about a point of fixation
Toxic effects of drugs
Rapid, conjugate, multidirectional, chaotic movements, often with widespread myoclonus
Many causes (same as for ocular flutter, above)
Treatment of neuro-ophthalmologic and cranial disorders depends on the cause