Skew Deviation

    • Vertical ocular misalignment as part of an inappropriate ocular tilt reaction
    • Produced by a lesion in the pathway that connects the inner ear (utricle/saccule) to the midbrain generators of torsional eye movements
    • Common causes: brainstem or cerebellar stroke, hemorrhage, tumor, demyelination
    • Uncommon causes: acute peripheral vestibulopathy (labyrinthitis/neuronitis), head trauma, neurodegenerative/infectious/ toxic/metabolic disorders
    • Core clinical features
      • Vertical diplopia (or blurred vision if the vertical misalignment is small)
      • Vertical misalignment that may be of small degree in all gaze positions (“comitant”) or of different degrees (“incomitant”)
      • Vertical misalignment that may show a right hypertropia in right gaze and a left hypertropia in left gaze (“alternating skew deviation”)
      • Vertical misalignment that may rarely be intermittent (“paroxysmal skew deviation”)
      • Trap: the vertical misalignment may be so small that it escapes detection with the Cover Test, but you can often detect it with the Single Maddox Rod test
      • Tip: the vertical misalignment pattern differs from that of fourth nerve palsy in not obeying the “three-step test” and lacking excyclodeviation in the higher eye (See Isolated Fourth Nerve Palsy )
    • Possible accompanying neurologic features
      • Saccadic pursuit
      • Gaze paresis
      • Nystagmus
      • Internuclear ophthalmoplegia
      • Ataxia
    • Imaging features
      • MRI may or may not show the responsible lesion, which can be very small
        or very large
    • Third nerve palsy
    • Fourth nerve palsy
    • Myasthenia gravis
    • Orbital inflammation, trauma, tumor
    • Look for saccadic pursuit, nystagmus, saccadic intrusions, and ataxia as defining accompaniments
    • Tip: if you do not find these accompaniments, question the diagnosis of skew deviation
    • Tip: skew deviation is unusual in peripheral vestibulopathy, so finding it--especially in combination with direction-changing horizontal nystagmus and a negative head impulse test--is strong evidence for a brainstem/cerebellar event (HINTS algorithm: “head impulse test negative, nystagmus, test of skew”)
    • Tip: Use the Single Maddox Rod Test to detect small vertical misalignments, especially when nystagmus or saccadic intrusions obscure fixational eye movements
    • Exclude a misalignment pattern that obeys the “three-step test,” which favors a diagnosis of fourth nerve palsy
    • Exclude torsional misalignment with the Double Maddox Rod Test, which favors a diagnosis of fourth nerve palsy
    • Tip: torsional misalignment is uncommon in skew deviation; when rarely present, the higher eye is incyclodeviated rather than excyclodeviated as it is in fourth nerve palsy
    • Order brain MRI if you suspect skew deviation
    • Ocular misalignment in skew deviation may persist, but often resolves faster than other clinical manifestations
    • Diplopia may be relieved with
      • Ground-in or press-on spectacle prisms
      • Eye patch
      • Spectacle occluder
      • Opaque contact lens
      • Extraocular muscle surgery

    Brainstem Ocular Motor Disorders

    Internuclear Ophthalmoplegia Skew Deviation Dorsal Midbrain Syndrome Thalamic or Tegmental Midbrain Syndrome Unilateral Pontine Syndrome Bilateral Pontine Syndrome Dorsolateral Medullary (Wallenberg) Syndrome Ototoxic Vestibulo-ocular Dysfunction Syndrome Acute Upgaze Deviation Acute Downgaze Deviation Acute Comitant Esotropia Omnidirectional Slow Saccades Omnidirectional Saccadic Pursuit