Sitting & Walking Oscillopsia in a Patient with Bilateral Vestibular Loss & Head Tremor

This is a 55-year-old man with oscillopsia for two reasons: He experienced oscillopsia at rest - so-called ‘sitting' oscillopsia - not from spontaneous nystagmus, but because of a combination of bilateral vestibular loss (BVL) and a mainly horizontal head tremor (this is sometimes referred to as "pseudonystagmus"). When evaluating the vestibulo-ocular reflex (VOR) at low frequencies (i.e., visually-enhanced VOR or vVOR), his intact smooth pursuit system supplemented the VOR, making the response look normal. At high frequencies (i.e., head impulse test, HIT), corrective saccades were seen, which is consistent with BVL. Additionally, vHIT gains were very low, although he had developed good compensatory covert saccades, which are eye movements that occur during the head movements. When the VOR was assessed in the mid frequency range (i.e., between vVOR and HIT), a saccadic appearance could be seen at the bedside due to VOR hypofunction. This VOR instability explains oscillopsia at rest in a patient with both BVL and head tremor. He experienced oscillopsia with head movements - so-called ‘walking' oscillopsia - this was due to VOR instability while walking or when moving the head. This is the most characteristic symptom of BVL. Unfortunately, even after a thorough work-up, the underlying etiology of his head tremor and BVL could not be elucidated. The onset was subacute, and he remained clinically unchanged (subjectively and objectively) over at least 6 months.