Sign · 4
Oscillopsia & diplopia
When the gaze-stabilising machinery fails, the world bounces. When the eyes drift out of alignment, the world doubles. Both complaints have a vestibular or brainstem cause more often than a primary ophthalmic one.
Oscillopsia — when the world bounces
Oscillopsia is the strange experience that the world is moving when it isn't — usually a bouncing or shimmering of the view during walking or head turns. The cause is a failed VOR: the eyes can't quite cancel the head movement, so the picture slides on the retina.
The most common cause is gentamicin or another aminoglycoside damaging both inner ears (bilateral vestibulopathy). Reading street signs becomes impossible while walking, and balance is much worse in the dark when vision can't compensate.
Bedside diagnosis rests on a positive head impulse test in both directions, a drop of more than two Snellen lines on dynamic visual acuity testing, and a history of ototoxic exposure, autoimmune inner-ear disease, or CANVAS. Patients describe head-movement-dependent blur and disabling unsteadiness in the dark; the cardinal feature is VOR insufficiency.1
Central oscillopsia accompanies pathological nystagmus — downbeat in primary gaze is a classic cause and often responds to 4-aminopyridine.3MS lesions of the cerebellar flocculus, paraflocculus, or nodulus give oscillopsia with associated pursuit and integrator deficits.
Mainstays of management are vestibular rehabilitation (gaze-stabilisation exercises with adaptation, substitution, and habituation strategies); meaningful improvement in DVA is achievable even in established bilateral loss.2 Aminopyridines for downbeat nystagmus, prisms for disabling diplopia, and rarely vestibular implants in selected centres round out the toolbox.
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A drop of more than two Snellen lines from static to dynamic acuity is the bedside criterion for VOR insufficiency. With vestibular rehabilitation, the dynamic deficit improves even when the peripheral loss is permanent.
Diplopia in vertigo
Sustained double vision in a vertiginous patient is a red flag — peripheral inner-ear disease essentially doesn't cause it. A short episode of double vision during a sudden nystagmus burst is one thing; persistent diplopia at rest is another and points centrally.
Vertical or oblique diplopia from skew deviation within the ocular tilt reaction is the commonest brainstem cause; horizontal diplopia from INO worsens on gaze toward the abducting (unaffected) side; cranial-nerve VI palsies (raised intracranial pressure, pontine lesions) and III palsies (with ptosis and mydriasis) appear within identifiable brainstem syndromes.4
Characterise the diplopia (horizontal, vertical, oblique; worse in which direction of gaze), then test for skew with alternate cover and for INO with horizontal saccades. Diplopia plus any other central neuro- ophthalmological sign should drive imaging. Symptomatic management — prism lenses, occlusion, and, for refractory cases, strabismus surgery — supplements treatment of the underlying lesion.