What is horizontal gaze nystagmus (HGN)?

Nystagmus is a condition in which the eyes involuntarily move and jerk in a repeated motion. When this movement occurs in a side-to-side manner, it’s called horizontal gaze nystagmus (HGN). If you’ve had too much to drink, you may experience impairment accompanied by HGN.

Testing for HGN is commonly performed as a way for law enforcement to detect drunk driving, although alcohol is not the only thing that can trigger the condition.