Incorrect

Incorrect

Incorrect

Correct! In pursuing a moving target, this patient’s eyes move in little jumps, rather than smoothly, as they should in following a target moving at this slow speed. This eye movement abnormality is called “saccadic pursuit,” in which a failure of the pursuit system causes the eyes to fall behind the moving target. Saccades, a more robust subsystem, fill in to allow the eyes to keep up. The replacement saccades generate this jerky movement. In this patient, saccadic pursuit is present as the eyes pursue in both horizontal directions (and it was also present in vertical pursuit, not shown here). This abnormality, called “omnidirectional saccadic pursuit,” is a sensitive sign of brain dysfunction, but is otherwise non-localizing. Common causes are neurotropic medications and toxins, but meningoencephalitis and increased intracranial pressure can also be at work. This patient had a paraneoplastic encephalitis. Trap: if you oblige the patient to follow a target moving above 30 degrees/second, you will elicit saccadic pursuit because even a normal pursuit system cannot handle such speeds. And here is another trap: inattentive patients or those who deliberately “tune out” the task of following a moving target with their eyes will also generate saccadic pursuit!