Final answer:
Poor vertical eye movement, involuntary saccades can be related to vestibulo-ocular reflex deficits or brain stem damage affecting eye movement nuclei. Testing eye movement involves tracking a stimulus without moving the eyes, and failure of one eye to move properly can result in double vision or diplopia.
Step-by-step explanation:
Poor vertical eye movement, involuntary saccades can be related to deficits in the vestibulo-ocular reflex (VOR) or brain stem damage affecting the eye movement nuclei or their connections. The VOR helps stabilize the visual field by compensating for head rotation with opposite rotation of the eyes. Testing eye movement involves having the patient track a stimulus without moving the eyes, and failure of one eye to move properly can result in double vision or diplopia.