Diplopia

Basics

Double vision
- Simultaneous perception of 2 images
- Can be oriented horizontally, vertically, or diagonally from one another
- Two types: monocular (ophthalmologic causes) and binocular (neurologic causes)
- Binocular and sixth nerve palsies most common
Diplopia is usually due to abnormal movement of the extraocular muscles (EOMs), which are innervated by 3 cranial nerves (CNs):
- CN 3 – superior, inferior, and medial rectus and inferior oblique muscles
- CN 4 – superior oblique muscle
- CN 6 – lateral rectus muscle
Brainstem lesions can damage CN nuclei or their connections (medial longitudinal fasciculus, MLF), causing an internuclear ophthalmoplegia (INO)
CN dysfunction:
- Compression as they traverse the subarachnoid space and venous sinuses
- Inflammation
- Elevation (or reduction) of CSF pressure can cause CN 6 palsy
Disease affecting the orbits and the bony skull can cause restriction of motion of one or both eyes or EOMs

Traumatic diplopia:
- Orbital fracture
- Contusions
- Hematoma
- Rarely brainstem contusion or hematoma
Monocular diplopia:
- Nearly always due to an intrinsic eye problem
- Corneal surface keratoconus
- Subluxation of the lens
- Structural defect within the eye
- Functional disorders such as conversion disorder, factitious disorder, or somatization
Nontraumatic binocular diplopia:
- Brain and brainstem dysfunction:
  - Stroke
  - Multiple sclerosis
  - Cerebral cortical problems (e.g., migraine) are rare
- CN dysfunction:
  - Aneurysm of posterior communicating artery (CN 3 palsy)
  - Chronic lymphocytic meningitis (multiple CN deficits)
  - Pseudotumor cerebri (CN 6 palsy)
  - Low pressure (spontaneous intracranial hypotension) (CN 6 palsy)
- Bony skull and orbits:
  - Tumor
  - Thyroid disease
  - Inflammation (Tolosa-Hunt)
- Neuromuscular junction (NMJ) of EOMs:
  - Myasthenia gravis (MG)

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