What are "vertical nystagmus" movements?

Vertical nystagmus refers to upward eye movements that are typically associated with severe intoxication or the use of certain drugs, particularly depressants like alcohol or stimulants. This type of eye movement is clinically significant as it can indicate a different level of impairment compared to horizontal gaze nystagmus, which is more commonly tested for in sobriety assessments. Abnormal vertical nystagmus is more likely to suggest the presence of certain drugs rather than alcohol alone, making it a critical observation for law enforcement and medical professionals assessing a person's level of impairment.

Other options describe different types of eye movement phenomena that do not accurately reflect what vertical nystagmus represents or how it is utilized for assessing intoxication levels. Thus, identifying upward eye movements linked with severe intoxication is consistent with recognized indicators of drug impairment.