What does vertical gaze nystagmus indicate?

Vertical gaze nystagmus is characterized by an involuntary jerking of the eyes when a person looks upward. This phenomenon typically indicates the potential presence of substance intoxication or impairment, particularly from certain depressants such as alcohol or specific drugs like phencyclidine (PCP) and other hallucinogens. The presence of vertical gaze nystagmus can be assessed during a field sobriety test to aid in determining whether a driver may be impaired.

The other options do not accurately describe vertical gaze nystagmus. For instance, slow eye movement refers to a different phenomenon and is not specific to the jerking movement observed in nystagmus. Difficulty focusing on objects pertains more to visual acuity issues rather than the specific eye movement characteristics of nystagmus. Clear vision during rapid movements is not related to nystagmus since, during this condition, the jerking is involuntary, causing disrupted or impaired vision rather than clarity.