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 Cranial Nerves ). One or more cranial nerves may be affected.
(See also Horner Syndrome Horner Syndrome Horner syndrome is ptosis, miosis, and anhidrosis due to dysfunction of cervical sympathetic output. (See also Overview of the Autonomic Nervous System.) Horner syndrome results when the cervical... read more , Optic Nerve Disorders The Optic Pathway The optic pathway includes the retina, optic nerve, optic chiasm, optic radiations, and occipital cortex (see figure Higher visual pathways). Damage along the optic pathway causes a variety... read more , and Approach to the Neurologic Patient Approach to the Neurologic Patient Patients with neurologic symptoms are approached in a stepwise manner termed the neurologic method, which consists of the following: Identifying the anatomic location of the lesion or lesions... read more .)
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.
(See also How to Assess the Cranial Nerves How to Assess the Cranial Nerves The cranial nerves originate in the brain stem. Abnormalities in their function suggest pathology in specific parts of the brain stem or along the cranial nerve's path outside the brain stem... read more .)
Evaluation of neuro-ophthalmologic and cranial nerve disorders includes the following:
Detailed questioning about symptoms
Visual system examination includes ophthalmoscopy and testing of visual acuity, visual fields Visual field testing The eye can be examined with routine equipment, including a standard ophthalmoscope; thorough examination requires special equipment and evaluation by an ophthalmologist. History includes location... read more , pupils Common Pupillary Abnormalities , and eye movements (ocular motility Common Disturbances of Ocular Motility ). As part of this testing, the 2nd, 3rd, 4th, and 6th cranial nerves 3rd, 4th, and 6th Cranial nerves The cranial nerves originate in the brain stem. Abnormalities in their function suggest pathology in specific parts of the brain stem or along the cranial nerve's path outside the brain stem... read more 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 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.
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 Diplopia Diplopia is the perception of 2 images of a single object. Diplopia may be monocular or binocular. Monocular diplopia is present when only one eye is open. Binocular diplopia disappears when... read more 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.
Treatment of the cause
Treatment of neuro-ophthalmologic and cranial disorders depends on the cause.