192	11 Diseases of the Cranial Nerves
		Table 11.5 Localization and etiology of abducens nerve palsy
		Site of lesion	Clinical features	Etiology
		Nuclear, pontine paramedian	gaze palsy, often combined with peripheral or	infarct, hemorrhage, tumor, multiple sclerosis, in-
		reticular formation	nuclear facial nerve palsy	flammation, trauma, congenital aplasia
		Fascicular	abducens palsy with contralateral hemiparesis,	infarct, hemorrhage, multiple sclerosis
			occasional also trigeminal deficit

Subarachnoid space

isolated abducens nerve palsy

Petrous apex, petrous bone deficits of CN V and VI, sometimes also VII and VIII

Cavernous sinus, superior abducens nerve palsy accompanied by orbital fissure dysfunction of CN III, IV, and V/1 in varying

combinations

intracranial hypertension, intracranial hypotension, aneurysm (AICA, PICA, basilar a.), subarachnoid hemorrhage, basilar meningitis, cranial polyradiculitis, trauma, neurosurgical complication, tumor of the abducens n., clivus tumor

extradural infection in otitis media

aneurysm (internal carotid a.), carotid−cavernous fistula, cavernous sinus thrombosis, parasellar tumor or pituitary tumor with parasellar extension, sphenoid sinusitis, Tolosa−Hunt syndrome, herpes zoster

Orbital apex	abducens palsy accompanied by dysfunction of
	CN III, IV, and V/1 in varying combinations
Orbit	isolated lateral rectus palsy, or combined with
	other deficits
No localizing significance	isolated lateral rectus (abducens nerve) palsy

see lists of causes above and below (cavernous sinus, orbit)

trauma, orbital tumor, orbital pseudotumor, endocrine ophthalmopathy, infection, mucocele

diabetes, hypertension, arteritis, migraine

eye movement are often due to brainstem processes; the differential diagnosis includes the entire spectrum of supranuclear oculomotor disturbances. In addition, disorders of neuromuscular transmission, such as myasthenia gravis (p. 275), and diseases of the eye muscles themselves must be considered, including myositis of the eye muscles (rare), mitochondrial myopathy (Kearns−Sayre syndrome), or endocrine ophthalmopathy in hyperthyroidism.

Ptosis

Ptosis is present when the upper lid covers the upper border of the pupil. The cause of ptosis can be myogenic, neurogenic, or mechanical (e. g., dehiscence of the levator aponeurosis).

The eyelid is actively elevated mainly by the action of the striated levator palpebrae m., which is innervated by the oculomotor n. Paralysis of this muscle causes ptosis that is most evident when the patient looks up. The eyelid is also held up, however, by the sympathetically innervated, smooth superior tarsal m. It follows that ptosis can be produced by lesions either of the oculomotor n. or of the sympathetic innervation of the eye. The causes of ptosis are listed in Table 11.6.

Horner syndrome is caused by loss of the sympathetic innervation of the eye and consists of:

ptosis (paralysis of the sympathetically innervated superior tarsal m.), most evident when the patient looks slightly downward;

miosis (paralysis of the sympathetically innervated dilator pupillae m.);

Table 11.6 Causes of ptosis

Pathogenesis	Causes (examples)
Mechanical factors	connective tissue defect (e. g.,
	dehiscence of levator aponeurosis)
	local orbital change
	microphthalmia
Muscle disease	progressive external ophthalmo-
	plegia
	Steinert myotonic dystrophy
Neuromuscular trans-	myasthenia gravis
mission disorder	botulism
Neurogenic: loss of inner-	oculomotor nerve lesion
vation	midbrain infarction
	cortical lesion
	sympathetic lesion (central or
	peripheral)
Neurogenic: excessively	blepharospasm
strong innervation	faulty regeneration after facial nerve
	palsy
	hemifacial spasm

mild enophthalmos (paralysis of Müller muscle, a smooth muscle in the orbit); and

conjunctival hyperemia (loss of the constrictive effect of the sympathetic nervous system on the conjunctival vessels).

When Horner syndrome is not accompanied by a loss of sweating in one-half of the face, the responsible lesion is located in the (ventral) roots of C8 through T2 proximal to their joining with the sympathetic chain. If it is accompanied by a loss of sweating in the face, neck, and

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Disturbances of Ocular and Pupillary Motility

arm on one side, then the lesion is at the stellate ganglion, or at a more cranial level of the sympathetic plexus in the neck. A lesion of the sympathetic chain immediately below the stellate ganglion impairs sweating in the ipsilateral upper quarter of the body without producing Horner syndrome. (It is worth noting that thoracic sympathectomy is sometimes performed at this site for the treatment of hyperhidrosis.)

Pupillary Disturbances

Pupillary motility is regulated by the parasympathetic portion of the oculomotor n. (sphincter pupillae m.) and by the sympathetic nervous system (ciliary m. = dilator pupillae m.). The constrictor and dilator muscles of the pupil are both smooth muscles; the parasympathetic nervous system constricts the pupil and the sympathetic nervous system dilates it. A lesion of the oculomotor n. thus produces a wide pupil, while a lesion of the sympathetic supply (e. g., in Horner syndrome) produces a narrow pupil.

Abnormalities of the Size and Shape of the Pupil

In pupillary ectopia, the pupil occupies an eccentric position in the iris. This may be due to a congenital malformation, an inflammatory disorder of the iris, or incomplete nerve regeneration after prior oculomotor nerve palsy. Abnormally shaped pupils are usually due to a congenital malformation. Mild inequality of pupillary size is a common, normal finding, but marked asymmetry is generally pathological. Inequality of the pupils is called anisocoria; its causes include Horner syndrome and Adie syndrome (see below) and others.

Abnormalities of the Pupillary Reflexes

Impairment of the direct and consensual pupillary light reflexes (p. 20) may be caused by any of the following:

Local affections of the eye, such as glaucoma or posterior synechiae.

The Marcus Gunn phenomenon is an impairment of the direct pupillary response to light on the side of a prior episode of retrobulbar neuritis.

Adie pupil (= pupillotonia) is usually unilateral, at least at first. The pupil is wider on the affected side and constricts very slowly in response to light, but promptly and completely on convergence. The subsequent widening of the pupil is slow (tonic). Women are more commonly affected than men; often, but not always, individual intrinsic muscle reflexes are absent. The pathogenesis of this condition is poorly understood. The underlying lesion is thought to lie either in the midbrain or in the ciliary ganglion.

Acute ciliary ganglionitis (after an infection or trauma) renders the pupil unresponsive to light or convergence.

Reflex pupillary rigidity (= Argyll Robertson pupil) is a typical finding in late neurosyphilis. The pupils are generally narrow, usually oblong, and unresponsive to light, but they constrict on convergence. It should be emphasized, however, that fixed and dilated pupils can also be seen in neurosyphilis.

The presence of a normal pupillary light reflex in a patient who is totally blind indicates bilateral damage to the visual pathway at some point between the lateral geniculate body and the visual cortex of the occipital lobe. The usual cause is bilateral infarction of the visual cortex. The light reflex is preserved because the nerve fibers subserving this reflex branch off the visual pathway proximal to the lateral geniculate body and travel to the pretectal area to innervate their target nuclei.

Hippus, a rhythmic fluctuation of pupillary width, is usually physiological.

The major abnormalities of pupillary size and responsiveness are summarized in Fig. 11.12.

193

Diseases of the Cranial Nerves

11

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194	11 Diseases of the Cranial Nerves
			Initial		Direct		Contralateral		Convergence		Characteristic features
			position		illumination		illumination
			right	left
		normal
		amaurotic									blind in right eye,
											normal reaction to atropine and
		fixed pupil
											physostigmine
		oculomotor nerve									ocular motility disturbed only in
											oculomotor nerve lesion;
		lesion (and ciliary
											contraction in response to
		ganglionitis)
											miotic agent
											normal ocular motility, tonic
		Adie pupil									dilatation after convergence
		(pupillotonia)									reaction, normal response to
											mydriatic agents
											pupils often misshapen, no
		Argyll Robertson									response to weak mydriatic
											agents, enhanced contraction
		pupil
											with physostigmine, mild
											dilatation with atropine
		early optic nerve
		lesion (afferent
		pupillary defect)
											normal ocular motility, no
		local atropine									contraction in response to
		effect									miotic agents, no constriction
											with physostigmine
		systemic atropine									no change with physostigmine
		effect
		diencephalic lesion									narrow, reactive
		midbrain lesion									fixed in midposition
		pontine lesion									fixed, pinpoint pupils
	Fig. 11.12 Abnormalities of the pupillary reflexes (right side abnormal).

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