What are possible eye indicators of someone under the influence of CNS depressants?

The presence of horizontal gaze nystagmus (HGN) and vertical gaze nystagmus (VGN) are significant eye indicators for someone under the influence of central nervous system (CNS) depressants. HGN refers to an involuntary jerking of the eyes when they are moved to the side, often observed during field sobriety tests. This eye movement can occur in individuals who have consumed depressants, indicating impairment.

Vertical gaze nystagmus (VGN) is similar but occurs when looking up and down. The presence of both HGN and VGN is a strong indicator that the individual may be under the influence of substances that depress brain function, such as alcohol or sedatives. Recognizing these eye indicators is essential for law enforcement during evaluations of potential impairments. Both forms of nystagmus are not commonly associated with other types of drugs or conditions, making them distinctive signs in assessing a person's state.