Skew Deviation

Skew deviation is a vertical misalignment of the eyes caused by dysfunction of the brainstem or cerebellum. Unlike fourth nerve palsy, which is a common cause of vertical diplopia, skew deviation indicates a central neurological problem.

Understanding Skew Deviation

Skew deviation occurs when the pathways that coordinate vertical eye position are disrupted. These pathways run through the brainstem, connecting the vestibular system to the eye muscles.

The result is one eye higher than the other—a hypertropia—but without the pattern expected from a single muscle or nerve problem.

Clinical Features

Eye Position

• One eye higher than the other (hypertropia)
• The misalignment may be:
  • Comitant: Same in all gaze directions
  • Incomitant: Varies with gaze direction
• May be accompanied by head tilt

Ocular Tilt Reaction

Skew deviation is often part of the "ocular tilt reaction" triad:

1. Skew deviation—vertical misalignment
2. Head tilt—toward the lower eye
3. Ocular torsion—rotational misalignment (cyclotorsion)

Associated Findings

• Nystagmus
• Internuclear ophthalmoplegia
• Other brainstem signs
• Vestibular symptoms (vertigo, imbalance)

Causes

Stroke

• Brainstem stroke (most common)
• Cerebellar stroke

Demyelinating Disease

• Multiple sclerosis
• Other demyelinating conditions

Other Causes

• Brainstem tumor
• Trauma
• Infection
• Chiari malformation

Distinguishing from Fourth Nerve Palsy

This is clinically important because the causes and implications are different:

Feature	Skew Deviation	Fourth Nerve Palsy
Torsion direction	Toward higher eye	Toward lower eye
Head tilt	Toward lower eye	Away from affected eye
Three-step test	Often inconsistent	Usually positive
Other neuro signs	Often present	Usually absent
MRI findings	Central lesion	Usually normal

Useful Tests

• Fundus photography: Shows direction of torsion
• Double Maddox rod test: Measures torsion
• Three-step test: May not follow classic pattern

Diagnosis

Clinical Examination

• Cover testing for vertical deviation
• Check torsion
• Neurological examination
• Look for associated findings

Imaging

• MRI brain with attention to brainstem
• Often shows stroke or demyelination
• May need MRI of cervical spine

Treatment

Treat Underlying Cause

• Stroke management
• MS treatment
• Address other causes

Manage Double Vision

• Prism glasses
• Occlusion (patching)
• Strabismus surgery if stable

Prognosis

• May improve as underlying condition resolves
• Stroke-related skew may improve over weeks to months
• Some patients have permanent deviation
• Prisms or surgery can help if persistent

When Skew Deviation Is Found