Test Your Knowledge - Oscillopsia

This 65-year-old man with multiple sclerosis described that objects in front of him appear to spontaneously jump or move horizontally for the last few months. He reported that his symptoms occur independent of head movements and head impulse testing was normal. After viewing the video, what is the most likely cause of his "jumping" vision? A. Gaze-evoked nystagmus B. Pendular nystagmus C. Bilateral vestibular loss D. Internuclear ophthalmoplegia (INO). A. Incorrect. This patient has gaze-evoked nystagmus (GEN) due to a defective gaze holding mechanism, also known as the neural integrator. The neural integrator is responsible for turning eye velocity commands into eye position commands so that gaze can remain stable in eccentric gaze. Common causes are drugs (e.g., antiepileptic medications), and when gaze-evoked nystagmus is present in all directions of gaze, this implies a lesion(s) involving the cerebellum (flocculus/paraflocculus) or its connections. However, gaze-evoked nystagmus would only cause oscillopsia in eccentric gaze. GEN is a form of jerk nystagmus as defined by alternating slow and fast phases. B. Correct. This patient has acquired pendular nystagmus (APN), which is demonstrated by back-to-back slow phase eye movements. APN will commonly cause significant "sitting" (independent of head movement) oscillopsia unless vision is very poor. Multiple sclerosis and oculopalatal tremor are the most common etiologies of APN. The APN seen with MS can be conjugate (both eyes move in the same direction with similar amplitude) or disconjugate (both eyes move in the same direction with different amplitude). When disconjugate, the more intense nystagmus is typically present in the eye with poorer vision. This led to the assumption that conduction delays of visual information due to optic nerve demyelination induce eye movements that are unsuccessful in holding the image on the retina (1). However, this theory cannot be the sole mechanism as APN often remains unchanged in dark. Momentary damping of the nystagmus for a few hundred milliseconds can occur after saccades, blinks or vibration applied on the skull (not shown in the video). This lends further support to the idea that APN probably also results from an abnormality in the gaze holding machinery, and saccades or blinks may serve to transiently "reset" the neural integrator (2). C. Incorrect. Bilateral vestibular loss (BVL) will commonly cause "walking oscillopsia" (dependent on head movement) as the impaired vestibulo-ocular reflex (VOR) cannot keep the retinas stable during head movements. This patient had normal head impulse testing. One exception where BVL can cause "sitting oscillopsia" is in the case of severe BVL and a tremor of the head and neck. A head and neck tremor in a patient with normal vestibulo-ocular reflexes shouldn't cause a visual disturbance or oscillopsia. But if the VOR is impaired enough, the oscillations of the tremor will constantly move the head (and eyes) slightly off the fixation point resulting in instability of the retinal images and oscillopsia. This is referred to as ‘pseudonystagmus' because while oscillopsia is experienced in straight ahead gaze, there is no true nystagmus. D. Incorrect. This patient has bilateral INOs, although there are no clear adduction deficits and adduction lag is only appreciated with horizontal saccades. While an INO may cause diplopia, some patients may only notice a blurring of vision with rapid eye movements. Acutely, a patient with a medial longitudinal fasciculus (MLF) lesion may have spontaneous vertical-torsional nystagmus due to vertical semicircular canal pathway imbalance which causes "sitting oscillopsia", but this was not present in this case. Occasionally a patient with MS may complain of "walking oscillopsia", and this often relates to bilateral MLF lesions. Since the vertical semicircular canal (posterior and anterior) pathways travel through the MLF, while the horizontal VOR is preserved, the vertical VOR may be hypoactive. Dynamic visual acuity and head impulses can both be used to interrogate horizontal and vertical VOR function. Finally, the abducting nystagmus due to an INO may cause mild oscillopsia in far lateral gaze similar to GEN, but not in straight ahead gaze. Discussion: This is an MS patient with conjugate horizontal pendular nystagmus (responsible for his oscillopsia), bilateral INOs (bilateral adduction lag with horizontal saccades and abducting nystagmus), gaze-evoked nystagmus, and hypermetric saccades (best seen in the abducting eyes during saccades since there is an adduction lag OU due to the INOs). Oscillopsia is defined as the illusion of movement of the stationary environment. It is a visual sensation and resolves with eyes closed. Vertigo is a false sensation of movement/motion and is a balance sensation that does not resolve with eyes closed. However, a vestibular condition like acute vestibular neuritis can result in oscillopsia due to spontaneous nystagmus (goes away with eyes closed), and vertigo (does not go away with eyes closed) - in this case, both nystagmus and vertigo are the result of asymmetric semicircular canal afferents. A diagnostic approach to determining the probable etiology of oscillopsia begins with an inquiry of whether oscillopsia is dependent on or time-locked to head movements ("walking" oscillopsia - e.g., BVL) or whether it is independent of head movements ("sitting" oscillopsia - e.g., nystagmus or instrusions). When oscillopsia is time-locked to head movement and patients see clearly when they stop moving their head, BVL is the most likely cause, and may be related to ototoxicity from aminoglycosides (e.g., gentamicin) or a variety of other etiologies (nutritional, neurodegenerative, etc). When oscillopsia is triggered by head movements, an etiology like benign paroxysmal positional vertigo (BPPV) should be considered, and Dix-Hallpike performed. Attacks of oscillopsia and vertigo are usually vestibular in origin, and may be due to vestibular migraine, Meniere's, vestibular paroxysmia, BPPV, superior canal dehiscence syndrome (triggered by loud noises and pressure) among others. Our patient had continuous oscillopsia at rest with no head tremor. This indicates the presence of spontaneous nystagmus in primary gaze, and patient indeed had a pendular nystagmus. He also had gaze-evoked nystagmus and bilateral INO, but these cause nystagmus in non-primary gaze and therefore should not elicit oscillopsia. 1. Averbuch-Heller L, Zivotofsky AZ, Das VE, DiScenna AO, Leigh RJ. Investigations of the pathogenesis of acquired pendular nystagmus. Brain 1995;118 ( Pt 2):369-378. 2. Ehling R, Lutterotti A, Brenneis C, Zee DS, Beh SC, Kheradmand A. Damping of monocular pendular nystagmus with vibration in a patient with multiple sclerosis. Neurology 2014;83:1879.