The Horizontal Gaze Nystagmus is a test that involves an officer requesting that a driver focus on a fixed object, which is usually his 
finger or a pen, and asking the driver to follow the objects movement using only his eyes without turning his hand. The officer is looking for a shaking or quivering of the driver’s pupil when administering the test.
The sooner the driver’s pupil begins to quiver while tracking the object, the more intoxicated the driver is said to be. This test is not administered as commonly these days due to the fact that it takes the officer skill and practice to be able to properly detect the intoxication of the driver.
We have a former police officer who currently works in our office, and she has reported that she has only administered the HGN test a couple of times. Further, she stated that she has never used the test without performing other field sobriety tests. She did report, however, that the more intoxicated the driver was, the more the pupil would quiver. However, she further stated that this was not the most accurate of tests, and it took a bit of experience and training to be able to administer the test properly.
