What are the causes of vertical diplopia?

Causes of Vertical Diplopia

Vertical diplopia arises from five major categories: superior oblique palsy (fourth nerve), skew deviation from posterior fossa lesions, oculomotor nerve palsy (third nerve), restrictive ophthalmopathies (especially thyroid eye disease), and myasthenia gravis. 1

Primary Etiologies by Anatomic Localization

Superior Oblique Palsy (Fourth Nerve)

• Most common cause of isolated vertical diplopia in adults 1
• Presents with hypertropia greatest in opposite lateral gaze and head tilt to the same side (Parks-Bielschowsky three-step test) 1
• The hypertropic eye demonstrates excyclotorsion (fundus extorsion) 1, 2
• Patients adopt compensatory head tilt away from the hypertropic eye to minimize diplopia 1
• Congenital cases (often decompensated in adulthood) show lax superior oblique tendon on forced ductions 1
• Acquired causes include head trauma, microvascular ischemia, and rarely trochlear schwannoma 1
• Giant cell arteritis can present as acute-onset superior oblique palsy in patients over 50 years 1, 2

Skew Deviation (Posterior Fossa Emergency)

• Critical to distinguish from fourth nerve palsy because skew demands urgent neuroimaging for stroke, demyelination, or mass lesion 1, 2
• Results from disruption of vestibulo-ocular pathways in the brainstem, cerebellum, or vestibular end-organ 1, 2
• Characteristic ocular tilt reaction: head tilt toward the hypotropic eye, with both eyes rotating in the direction of head tilt 1, 2
• The hypertropic eye shows incyclotorsion (opposite pattern from fourth nerve palsy) 1, 2
• May be comitant or incomitant, making the three-step test unreliable for differentiation 1, 2
• Upright-supine test: hypertropia reduces >50% when supine (80% sensitivity, 100% specificity) in chronic cases, but unreliable in acute presentations (<2 months) 1, 2
• Common etiologies: acute vestibular neuronitis, posterior circulation stroke, demyelinating disease 1, 2

Oculomotor Nerve Palsy (Third Nerve)

• Produces vertical diplopia with ptosis and impaired adduction 1
• Pupil-involving third nerve palsy requires urgent MRA/CTA to exclude posterior communicating artery aneurysm 1, 3
• Pupil-sparing third nerve palsy in patients with vascular risk factors suggests microvascular ischemia, but neuroimaging still recommended if not improving by 3 months 1
• Complete third nerve palsy causes hypotropia and exotropia with inability to elevate, depress, or adduct the eye 1

Restrictive Ophthalmopathies

• Thyroid eye disease is the most common restrictive cause, presenting as new-onset vertical diplopia with positive three-step test that mimics superior oblique palsy 1
• Look for proptosis, lid retraction, resistance to retropulsion, and enlarged extraocular muscles on imaging 1
• Inferior rectus restriction is most common, causing limitation of elevation 1
• Orbital trauma, tumors, and orbital inflammatory disease also cause restrictive vertical diplopia 1

Myasthenia Gravis

• Presents with fatigable vertical diplopia, often worse at end of day 4, 5
• May have variable pattern of misalignment that doesn't fit cranial nerve distribution 4, 5
• Associated findings: fatigable ptosis, orbicularis weakness (inability to bury lashes), and positive ice pack test 4
• Acetylcholine receptor antibodies positive in 50% of pure ocular myasthenia; consider MuSK antibodies if seronegative 4

Age-Related Causes

Older Adults (>50 years)

• Divergence insufficiency and sagging eye syndrome cause esotropia with small vertical component, more common in seventh decade 1
• Sagging eye syndrome associated with blepharoptosis (29%) and deep superior sulcus defect (64%) 1
• Microvascular ischemia affecting third, fourth, or sixth nerves in patients with diabetes, hypertension 1, 6

High Myopes

• Strabismus fixus (heavy eye syndrome) in axial length >27mm causes progressive esotropia with hypotropia and mechanical restriction 1

Critical Red Flags Requiring Urgent Neuroimaging

Obtain emergent brain/brainstem MRI with and without contrast for: 1, 2

• Any additional neurological signs or symptoms beyond isolated diplopia
• Small vertical fusional amplitudes without trauma history (suggests acquired cause like trochlear schwannoma)
• Pupil-involving third nerve palsy (aneurysm until proven otherwise)
• Suspected skew deviation (any posterior fossa signs)
• Patients over 50 with acute onset (exclude giant cell arteritis, stroke)

Diagnostic Algorithm

1. Determine pattern of misalignment using cover test in nine gaze positions 1, 7

2. Apply Parks-Bielschowsky three-step test for isolated vertical deviation 1

   • Step 1: Which eye is hypertropic in primary gaze?
   • Step 2: Is hypertropia worse in right or left gaze?
   • Step 3: Is hypertropia worse with head tilt right or left?

3. Assess fundus torsion to distinguish fourth nerve palsy (excyclotorsion of hypertropic eye) from skew (incyclotorsion of hypertropic eye) 1, 2

4. Perform upright-supine test if skew suspected: >50% reduction in hypertropia when supine suggests chronic skew 1, 2

5. Check for restrictive disease with forced ductions, proptosis measurement, and resistance to retropulsion 1

6. Test for myasthenia with fatigable upgaze, ice pack test, and orbicularis strength 4

Common Pitfalls

• Do not assume benign etiology even with isolated vertical diplopia—11% of skew deviation cases have no other neurologic signs 2
• Do not rely solely on three-step test to exclude skew deviation, as it can perfectly mimic fourth nerve palsy 1, 2
• Do not delay imaging in patients with poor fusional amplitudes or atypical features 1, 2
• Do not miss thyroid eye disease presenting as "superior oblique palsy"—check for proptosis and lid signs 1
• Do not overlook giant cell arteritis in elderly patients with new vertical diplopia—check ESR/CRP urgently 1, 2