Diplopia

Perspective

Diplopia, or double vision, comes in two varieties—monocular and binocular—and constitutes approximately 1.4% of ophthalmologic emergencies. For patients who visit the emergency department (ED) with diplopia, the majority of cases are binocular, with cranial nerve (CN; especially sixth nerve) palsies being among the most common causes.¹ The remainder (approximately 15%) are monocular.

Pathophysiology

Monocular diplopia, or double vision that persists in one affected eye even with the other eye closed, is an ophthalmologic problem related to distortions in the light path.

Binocular diplopia, or double vision that resolves when either eye is closed, is the result of a misalignment in the visual axes and has a wide range of causes, which can be organized in a progression from the eye, distally, to the brainstem, proximally. The culprit process might involve oculomotor muscle dysfunction, CN dysfunction, or intranuclear or supranuclear lesions in the brainstem or above.

Diagnostic Approach

The refinement of the differential diagnosis for the ED patient with diplopia involves parsing out the exact nature of the diplopia, determining the functional location of the defect, and screening for associated symptoms and findings that may suggest the underlying cause. The majority of this diagnostic resolution is done at the bedside, followed by targeted neuro-ophthalmologic imaging as indicated. The causes of diplopia are myriad, with pathologies relatively benign to relatively fulminant, and the tactical approach to diplopia in the ED entails sorting out those that may result in rapid and profound morbidity from those that are less acute. Table 21-1 outlines some key causes of diplopia prioritized by immediate acuity, with mechanism and distinguishing features.

Table 21-1

Important Causes of Diplopia

DIPLOPIA-CAUSING ENTITY	MECHANISM AND MORTALITY	DISTINGUISHING FEATURES
Tier 1—Critical
Basilar artery thrombosis	Acute thrombosis of the basilar artery with brainstem ischemia; untreated, mortality 70-90%	Vertigo, dysarthria, other cranial nerve involvement; risk factors for stroke
Botulism	Toxin inhibits of release of acetylcholine (ACh) at cholinergic synapses and presynaptic myoneural junctions; untreated, mortality 60%	Dysarthria, dysphagia, autonomic dysreflexia, pupillary dysfunction
Basilar meningitis	Infection; untreated, mortality close to 100% if bacterial (25-40% if treated)	Headache, meningismus, fever
Aneurysm	Enlarging aneurysm directly compresses cranial nerve; untreated, rupture risk is 1% per year; mortality 26-50% per rupture	CN III palsy with pupillary involvement
Tier 2—Emergent
Vertebral dissection	Dissection causes vertebrobasilar ischemia; acute untreated, mortality 28% (2-5% if neurologically asymptomatic)	Neck pain, vertigo; risk factors for vertebral dissection
Myasthenia gravis	Autoantibodies develop against ACh nicotinic postsynaptic receptors; untreated, crisis mortality 42% (5% if treated)	Fluctuating muscle weakness, ptosis, and diplopia worsen with activity and improve with rest
Wernicke’s encephalopathy	Thiamine-dependent metabolic failure and tissue injury; untreated, mortality 20%	Nystagmus, ataxia, altered mental status, and ophthalmoplegia; risk factors and nutritional deficiency
Orbital apex syndrome, cavernous sinus process	Inflammation or infection in the orbital apex or cavernous sinus directly affects oculomotor cranial nerves; acute mortality low unless infectious and complicated by meningitis	A combination of palsies of CN III, IV, or VI, with retro-orbital pain, conjunctival injection, and possible periorbital or facial numbness
Tier 3—Urgent
Brainstem tumor	Tumor involvement at the supranuclear level; acute mortality low (long-term mortality variable)	Skew deviation vertical diplopia, internuclear ophthalmoplegia
Miller-Fisher syndrome	Autoantibodies develop to a cranial nerve ganglioside, GQ1b; acute mortality low if fully differentiated from GBS; mortality 2-12% if GBS	Ophthalmoplegia, ataxia, areflexia
Multiple sclerosis	Demyelinating lesions; acute mortality low	Internuclear ophthalmoplegia
Thyroid myopathy (Graves’ disease)	Autoimmune myopathy; acute mortality low with regard to ocular complaints	Proptosis, restriction of elevation and abduction of the eye, signs of Graves’ disease
Ophthalmoplegic migraine	Inflammatory cranial neuropathy; low mortality—self-limited disease	Ipsilateral headache, CN (usually III) palsy
Ischemic neuropathy	Microvascular ischemia; mortality low—self-limited disease	Isolated CN palsy (pupil-sparing if CN III)
Orbital myositis, pseudotumor	Autoimmune or idiopathic myositis; acute mortality low with regard to ocular complaints	Eye pain, restriction of movement, periorbital edema; exophthalmos and chemosis when more severe
Orbital apex mass	A tumor, infiltration, or mass effect in the orbital apex or cavernous sinus directly compresses oculomotor cranial nerves; acute mortality low	A combination of palsies of CN III, IV, or VI, and possible periorbital or facial numbness, with retro-orbital pain, proptosis, signs of venous congestion

CN, cranial nerve; GBS, Guillain-Barre syndrome.

There are four aspects of questioning that guide the formulation of the differential diagnosis: (1) the cadence of onset and symptoms, (2) the directionality and orientation of the diplopia, (3) the presence of pain, and (4) the presence of other associated symptoms.2,3 In terms of the cadence of onset, a truly sudden onset suggests an ischemic cause, either cerebrovascular or microvascular, especially if the intensity or degree of diplopia was maximal at onset. A fluctuation of symptoms over time may suggest transient ischemic attacks or an impending stroke but also generally implies a neuromuscular disease.^2,3 Regarding the directionality of the diplopia, the directions of gaze that elicit or worsen the diplopia, and the general orientation of that diplopia—that is, horizontal, vertical, or torsional—should be carefully determined in order to localize the problem. Finally, symptoms associated with the diplopia (such as pain or neurologic or neuromuscular symptoms) are critical to forming a differential diagnosis, if not to making the diagnosis. The presence of pain suggests an inflammatory or infectious process and narrows the differential significantly.

The Examination

The patient complaining of diplopia should undergo a thorough neurologic examination with attention to the CNs and an evaluation of the six cardinal movements of gaze. Each extraocular muscle (and the nerve that supplies it) has a maximal action in a specific direction, and the evaluation of gaze should therefore specifically follow the configuration of a six-limbed asterisk, or an H² (Fig. 21-1). The patient should also undergo a careful pupillary and facial examination for signs of pupillary asymmetry, ptosis, lid lag, conjunctival injection or chemosis, periorbital swelling, or proptosis² and assessment of overall head positioning.

Figure 21-1 Cardinal movements of the eyes, with the oculomotor muscles that create them, and the nerves that supply those muscles. Small curved arrows denote intorsion or extorsion of the eye by the muscle indicated. CN, cranial nerve.

The Diagnostic Approach

The acuity of onset and presence or absence of pain can be used to prestratify diagnostic possibilities as shown in Figure 21-2, especially with regard to vascular, potentially ischemic events. Through use of the lines of questioning and examination elements outlined previously, the differential diagnosis can then be rapidly winnowed down by means of a phased, systematic approach that incorporates the following queries (reflected in the algorithm in Figure 21-3):