In the context of SFST, which type of nystagmus is most commonly evaluated?

The assessment of Horizontal Gaze Nystagmus (HGN) is a crucial component of the Standardized Field Sobriety Test. This type of nystagmus is specifically evaluated because it is highly indicative of impairment due to alcohol consumption. During the HGN test, an officer observes the subject's eyes as they follow a moving stimulus, typically a pen or flashlight, to determine if an involuntary jerking motion occurs at certain angles.

Research has shown that at heightened levels of blood alcohol concentration, the presence of HGN increases, making it a reliable indicator for assessing a person's level of impairment. HGN provides measurable evidence which can be used in a legal context, enhancing the validity of the sobriety assessment when compared to other types of nystagmus which may not correlate as strongly with intoxication.

While resting nystagmus, post-rotational nystagmus, and caloric nystagmus exist, they are not commonly utilized in the field sobriety testing context. Resting nystagmus may indicate a potential medical condition unrelated to alcohol, while post-rotational and caloric nystagmus are typically studied in clinical or laboratory settings, making them less applicable in roadside sobriety evaluations