Correct! You can see why the patient is reporting that viewed objects appear to oscillate (an illusion called “oscillopsia”)! She has seesaw nystagmus, a pendular oscillation in the torsional plane; one eye rises and intorts, the other eye falls and extorts. Seesaw nystagmus arises from a disturbance in the diencephalic and rostral midbrain generators of torsional gaze. Sellar tumors—craniopharyngiomas

, pituitary adenomas, and other masses can compress the diencephalon and rostral brainstem to cause this form of nystagmus. It may also be a congenital finding without apparent structural alterations in the brain. Chiari malformation causes downbeat nystagmus. Multiple sclerosis causes an acquired pendular nystagmus, but it does not have this seesaw pattern. Superior oblique myokymia causes fine jerky torsional movements restricted to one eye. Downbeat and acquired pendular nystagmus are other common causes of oscillopsia because they share with seesaw nystagmus a relatively wide-amplitude slow phase. Superior oblique myokymia causes a momentary illusion of visual blur or diplopia and a sensation that the affected eye is twitching.