Sixth Cranial Nerve Palsy (Abducens Nerve Palsy)

Sixth cranial nerve palsy affects the abducens nerve, which controls the lateral rectus muscle—the muscle that moves the eye outward. When this nerve is damaged, the affected eye can't look toward the side, causing horizontal double vision that's worse when looking in that direction.

What the Sixth Nerve Controls

The sixth cranial nerve (abducens nerve) controls only one muscle: the lateral rectus. This muscle:

• Moves the eye outward (away from the nose)
• Works with the medial rectus of the other eye for coordinated gaze

Symptoms

Visual Symptoms

• Horizontal double vision—images side by side
• Worse looking toward affected side
• Better looking toward the opposite side
• Better at near (convergence helps)
• May turn head toward affected side to compensate

Eye Position

• Eye may appear turned inward (esotropia) in primary gaze
• Can't fully move eye outward
• Movement inward is normal

Causes

Microvascular (Most Common in Adults)

• Associated with diabetes, hypertension, hyperlipidemia
• Typical patient: older adult with vascular risk factors
• Usually isolated (no other neurological signs)
• Spontaneous recovery in 2-3 months

Elevated Intracranial Pressure

The sixth nerve has a long course through the skull and is sensitive to pressure changes:

• Idiopathic intracranial hypertension (IIH)—especially young overweight women
• Tumors—any mass causing increased pressure
• Hydrocephalus
• May have papilledema and headaches

This is a "false localizing sign"—the sixth nerve palsy doesn't mean the problem is near the sixth nerve.

In Children

Requires careful evaluation:

• Tumors (especially brainstem)
• Increased intracranial pressure
• Post-infectious inflammation
• Never assume microvascular in children

Other Causes

• Trauma
• Inflammation (sarcoidosis, multiple sclerosis)
• Tumors along nerve pathway
• Infection
• Cavernous sinus disease (often with other cranial nerve palsies)
• Giant cell arteritis in elderly

Evaluation

Key Questions

• Age of patient
• Vascular risk factors (diabetes, hypertension)
• Associated symptoms (headache, other neurological signs)
• Trauma history
• Speed of onset

Examination

• Eye movement assessment
• Look for papilledema
• Other cranial nerves
• Complete neurological exam

When Imaging Is Needed

Definitely needs imaging:

• Children
• Young adults without vascular risk factors
• Associated signs/symptoms (papilledema, headache, other nerve palsies)
• Bilateral sixth nerve palsy
• No improvement by 3 months
• Progressive worsening

May be observed:

• Classic microvascular presentation (older adult with diabetes/hypertension, isolated palsy)
• Still needs close follow-up

Tests

• MRI brain (with attention to brainstem and skull base)
• Blood tests (glucose, HbA1c, ESR/CRP in elderly)
• Lumbar puncture if elevated pressure suspected

Treatment

For Microvascular Sixth Nerve Palsy

• Observation—usually recovers in 2-3 months
• Control risk factors—optimize diabetes, blood pressure
• Symptomatic treatment for double vision:
  • Patching one eye
  • Fresnel prism (temporary stick-on prism)

For Underlying Cause

• Treat tumor, hydrocephalus, IIH, or other identified cause
• May need neurosurgery, medication, or shunting

If Persistent (6+ Months)

• Prism glasses for small deviations
• Strabismus surgery:
  • Medial rectus recession
  • Lateral rectus resection
  • May need adjustable sutures
  • Botulinum toxin injection to medial rectus sometimes used

Prognosis

Microvascular

• 80-90% recover spontaneously
• Most improvement within 3 months
• May have mild residual deviation
• Recurrence possible

Other Causes

• Depends on underlying condition
• Traumatic may be permanent
• Post-tumor treatment variable

Frequently Asked Questions

Why is my double vision worse when I look to one side?

The sixth nerve moves the eye outward. When you look toward the affected side, you're asking that weak muscle to work hardest. The eye can't keep up with the other eye, causing maximum separation and worse double vision.

Can I just close one eye?

Yes, patching or closing one eye eliminates double vision temporarily. Alternate which eye you patch to avoid constantly relying on one eye. Fresnel prisms are another temporary option.

Do I need an MRI?

It depends on your age, risk factors, and clinical presentation. Classic microvascular presentations in older adults with diabetes may be observed. Children, young adults, or anyone with atypical features needs imaging.

How long until I recover?

Microvascular sixth nerve palsies typically begin improving within weeks and are mostly recovered by 3 months. If not improving by then, your doctor will want to do additional testing.

Will this happen again?

There's about a 25% chance of having another cranial nerve palsy if you have ongoing vascular risk factors like diabetes. Controlling these conditions reduces recurrence risk.

Can I drive?

Double vision makes driving unsafe and often illegal. Once the double vision resolves (naturally or with prism), you can discuss returning to driving with your doctor.

References