Differential Diagnosis of Diplopia

Initial Classification and Anatomical Localization

The American Academy of Ophthalmology recommends immediate anatomical localization to distinguish between monocular and binocular diplopia, with binocular diplopia representing the majority of neurologically significant cases requiring systematic evaluation of the extraocular muscles, cranial nerves III/IV/VI, neuromuscular junction, and central pathways 1, 2
Sixth nerve palsy is the most common cranial neuropathy, characterized by horizontal diplopia worse at distance and in lateral gaze toward the affected side, with vasculopathic causes accounting for the majority in adults, typically resolving within 6 months 2, 3
The American Academy of Neurology suggests that third nerve palsy presents with combined horizontal and vertical diplopia, ptosis, and accommodative difficulty, with critical distinction between pupil-involving and pupil-sparing types 1, 3, 4

Fourth nerve palsy is characterized by vertical diplopia worse in downgaze and reading, with an annual incidence of 6.3 per 100,000, more common in males, and most commonly caused by trauma 1, 5, 6
Internuclear ophthalmoplegia is a lesion of the medial longitudinal fasciculus in the brainstem, with primary considerations including demyelinating plaque in younger patients and stroke in older patients with acute onset 1, 2

Thyroid eye disease is the most common cause of restrictive strabismus in adults, with inferior and medial rectus muscles most frequently affected, and diplopia occurring in 58-68% of orbital blowout fractures 7, 8
Orbital trauma can cause diplopia, with multiple mechanisms including muscle avulsion, entrapment, hemorrhage, edema, fracture, and cranial neuropathies, and diplopia persisting beyond 6 months is unlikely to resolve spontaneously 7, 8

Myasthenia gravis is characterized by variable, fatigable diplopia and ptosis, with 66-85% responding to corticosteroids, and acetylcholine receptor antibody testing is diagnostic 9, 10

Posterior circulation stroke can cause acute diplopia, and requires urgent vascular imaging, such as CTA, MRA, or DSA 1
Decompenated childhood strabismus can cause fixation switch diplopia, with common triggers including monovision correction, myopia development in the preferred eye, and incorrect refractive correction 9, 10

Pupil-involving third nerve palsy is a critical red flag requiring urgent evaluation, as it may indicate an aneurysm or other compressive etiology 1
Multiple cranial nerve palsies, acute onset with posterior circulation symptoms, papilledema or elevated IOP, and giant cell arteritis symptoms in the elderly are also critical red flags requiring urgent evaluation 1, 2, 3, 4, 5, 6
Neuroimaging, such as MRI brain and orbits with contrast, is indicated for young patients without vasculopathic risk factors, pupil-involving third nerve palsy, multiple cranial neuropathies, progressive symptoms or failure to resolve, and additional CNS signs 1, 3, 4, 5, 6