Ocular motility testing in the evaluation of visual hallucinations.

Distinguishing organic visual hallucinations from those caused by hysteria or malingering is important but difficult. We found that ocular motility testing is helpful in making the distinction in some patients who allege that their hallucinations move. A 9-year-old girl thought to have organic hallucinations, possibly caused by an occipital lobe neoplasm, was unable to generate smooth pursuit movements when she attempted to follow the movements of the hallucinations. Instead, she executed a series of small downward saccades. Her hallucinations were presumably stress-induced. Conversely, a 62-year-old man with hypertension, arteriosclerotic heart disease, and depression, whose hallucinations were thought to be hysterical, was able to execute smooth pursuit movements when he attempted to follow the hallucinations. Detection of a previously unrecognized visual field defect helped to establish that the hallucinations were organic. Thus, patients with moving organic hallucinations may produce smooth pursuit movements when attempting to follow the hallucinations, but patients with feigned or hysterical hallucinations, who lack a fixation target, are likely to execute a series of saccades.