Chapter 32 A common cause of horizontal double vision in clinical practice is abducens, or sixth nerve palsy. This chapter explores the common causes of abducens palsy and describes their clinical presentation. In general, patients with new-onset double vision should be evaluated by an ophthalmologist or neurologist within several days of onset. An exception to this dictum would be the patient with painful ophthalmoplegia or with ptosis and a dilated pupil, who should be evaluated emergently. Abducens palsy can occur in patients of any age from a variety of causes, both intrinsic to the nerve or brainstem (particularly ischemia and inflammation) and extrinsic or compressive phenomena (particularly neoplasm and aneurysm), as well as from closed head trauma. Microvascular ischemia is a common cause in older patients, particularly if there is a history of diabetes or hypertension. In a large series studied at the Mayo Clinic, undetermined cause was the largest diagnostic group followed by neoplasm, head trauma, vascular, aneurysm, and other miscellaneous causes. Patients with good vision in each eye complain of binocular, horizontal diplopia, which disappears when either eye is covered. Patients with poor vision in one eye, or separation of images so great that they do not appreciate both images simultaneously, may instead complain of misalignment of their eyes, with one turned inward. Pain may be present, depending on the cause of the sixth nerve palsy. Even vasculopathic sixth nerve palsies may give pain, and any expanding lesion in the cavernous sinus is likely to produce a painful abducens palsy. Depending on the cause of the palsy, other neurologic symptoms may occur, such as facial paralysis with involvement of the facial nerve in the case of a brainstem lesion causing the abducens palsy. A Horner’s syndrome and long tract signs, as well as gaze palsy or internuclear ophthalmoplegia, may also suggest a brainstem lesion. Involvement of other ocular motor nerves may occur in the cavernous sinus or orbit. A patient with an abducens palsy has one eye turning in (esotropia) relative to the eye that is fixing on the target. The maximum esotropia is on gaze to the side of the palsy, and there is minimal or no esotropia on gaze to the opposite side (Fig. 32–1). Either complete or relative inability to abduct the eye of the nerve involved should be seen. If other ocular motor nerves are involved, the patient’s ocular motility should reflect that, for example, a combined complete abducens and oculomotor nerve palsy on one side produces an eye with a ptotic lid, dilated pupil and essentially no observable movement in any direction except down and inward from action of the trochlear nerve. If an abducens palsy is secondary to raised intracranial pressure, in most cases the optic nerve heads are swollen; that is, they show papilledema.
SIXTH NERVE PALSIES
URGENCY OF EVALUATION
DIAGNOSIS
DEMOGRAPHICS AND ETIOLOGY
SYMPTOMS
Pain
Other Neurologic Symptoms
SIGNS
Motility
Optic Discs
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