What can cause Vertical Gaze Nystagmus (VGN) during testing?

Vertical Gaze Nystagmus (VGN) is a specific type of eye movement that can be observed during the Standardized Field Sobriety Tests to help determine impairment, particularly related to alcohol or certain drugs. When a person is under the influence of a high dose of alcohol or specific narcotics, their ability to control eye movement can be disrupted, resulting in nystagmus. This disruption manifests as an involuntary jerking of the eyes when they are moved vertically.

Understanding the physiological effects of substances like alcohol on the central nervous system is crucial for identifying signs of intoxication during a field sobriety test. Alcohol depresses the nervous system, affecting muscle coordination and control, which includes the muscles that govern eye movement. In contrast, options like low blood sugar, fatigue, or bright lights may also influence eye function but do not specifically relate to the known indicators of drug or alcohol impairment as directly as a high dose of substances does.