Previously on the Raleigh DWI Attorney Blog I have discussed North Carolina DWI Stops and the administration of Field Sobriety Tests; specifically the Walk and Turn Test and the One-Legged Stand Test. I will now review the third test, known as the Horizontal Gaze Nystagmus Test. As a Durham DWI Attorney and a Raleigh DWI Attorney, I believe having an understanding of each of these tests is important.
This test is familiar to most as the test whereby the Driver is asked to keep their head still while they track a stimulus as it moves in front of their face. A common misconception regarding this tests is that it is designed to see whether you are able to follow the stimulus without moving your head. And while that will likely be recorded if you are not able to do so, that is not the main purpose of the tests. Below I will review how the test is administered as well as what 'clues' the Police Officer is looking for.
To begin, the officer asks the Driver to keep their head still. The Officer should look to make sure the Driver's pupils are equal and that the eyes track evenly, that is, both eyes move together. The Police Officer will then move the stimulus (normally a pen, small light, or their finger) from the center of the Driver's face towards the Driver's shoulders keeping it 10-12 inches from the Driver's face. The Police officer will do this several times. Eventually, the Police Officer will hold the stimulus out towards the outside of the Driver's Peripheral vision.
During the first part of the test, as the stimulus is moved back and forth, the Officer is looking for what is known as 'smooth pursuit.' Smooth pursuit is where the eyes track the stimulus smoothly. Someone who may be intoxicated may have trouble with this and their eyes will 'fall behind' and then 'catch up' to the stimulus.
Next, the officer will look for what is called Nystagmus prior to the eyes reaching 45 degrees from the center of their face. Nystagmus is an involuntary twitching of the eye. This twitching can be caused by many things, but can be present when someone is intoxicated. For this test, the Officer is looking for Nystagmus to appear in the eyes prior to the eye reaching the 45 degrees previously mentioned.
Lastly, the officer will hold the stimulus out to the edge of the Driver's vision. The stimulus should be held there for at least 4 seconds. The Officer is looking for 'distinct' Nystagmus when the eyes are looking to their peripherals. Though this is normally present even in sober people, since the eye grows tired of holding that position, those that are intoxicated can have a more 'distinct' Nystagmus that Officers are trained to spot.
For these three tests, the officers are looking for 6 clues, 3 per eye: 1. lack of smooth pursuit, Nystagmus prior to onset of 45 degrees, and Nystagmus at maximum deviation (looking at your peripherals).
Occasionally, the Officers will also perform a Vertical Nystagmus test where they will hold the stimulus towards the upper part of the Driver's vision. Nystagmus at this point tends to appear in those who are substantially impaired.
