At what degree does the onset of nystagmus typically occur during the HGN test?

The onset of nystagmus during the Horizontal Gaze Nystagmus (HGN) test typically occurs at an eye gaze angle of 45 degrees. This is a critical point in the assessment of potential impairment due to alcohol consumption or other factors affecting a person's ability to coordinate their eye movements. Performing the HGN test involves observing the eyes as they follow a slowly moving target, and specifically, the examiner looks for the involuntary jerking of the eyes, known as nystagmus.

At 45 degrees, the eyes begin to show signs of nystagmus with even slight alterations in the subject's balance or ability to concentrate. If nystagmus appears at this angle, it can suggest a higher blood alcohol concentration (BAC) level, indicating potential impairment.

Understanding this is crucial for law enforcement officers and professionals conducting these tests, as this particular angle is a key marker in determining intoxication levels in subjects being evaluated.