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What is the DWI Eye Test?

The DWI eye test is called the Horizontal Gaze Nystagmus. This is the first of the three “standard” DWI tests. During this test an officer might have a pen-light or might use a finger illuminated by a flashlight. The officer will move the light or the finger to the left and right. The purpose of the test is to see if there is any involuntary jerking of the eye. There is a second part of the test that looks for “vertical” nystagmus, but that is not considered “standardized” like the HGN.

As part of the test, police instruct you to follow the light/finger with your eyes only. Though moving your head during the test is not technically a clue, police will use the movement against you. The same can be said of swaying during the test. The HGN test does not test for swaying, but police will say that swaying during the test indicates impairment. Though it can and does vary depending on training, many officers consider the HGN to be the test which best indicates impairment. This begs the question:

Is the DWI Eye Test Accurate?

The short answer is “not exactly”. Like the other tests, the DWI Eye Test does not predict impairment. The test is mostly designed to correlate performance with the probability of being above a particular BAC. The main issue, however, is that the DWI Eye Test is actually a very complex test. The DWI Eye Test is primarily based on tests that doctors and other medical personnel use to diagnose neurological function. For example, it is a test that a doctor might use to diagnose a head injury. Most officers do not have the scientific or medical training to properly conduct such a complex test. Further, officers usually conduct the DWI eye test where outside forces might impact the performance and results of the test.

There are at least 86 different types of nystagmus. In other words, Horizontal Gaze Nystagmus is only 1 of a possible 86. Most officers do not receive training in differentiating between all of these varieties. Even narrowed to HGN, officers do not receive instruction on the various causes of HGN. Horizontal Gaze Nystagmus might occur due to factors like the flu, vertigo, epilepsy, and hypertension (among others). HGN might even occur due to having too much caffeine! That means a person who had a bunch of soda but no alcohol might still “fail” the DWI Eye Test!

Overall, the DWI Eye Test is not very accurate. At the same time, it is not wholly inaccurate. Even minor alcohol impairment (e.g., around .04) might cause HGN. However, the problems with the DWI Eye Test lie mostly in the minimal training received by officers and the complexity of the test itself. Like with the other DWI tests, the eye test tends to be very subjective. In short, the DWI eye test is not a good indication of impairment.

More about Mimi Coffey & The Coffey Firm

When people look for a Top DWI Attorney or Best DWI Attorney, they look for experience, certification, and respect in the legal community. Mimi Coffey is a nationally-renowned trial attorney, board-certified in DWI by the NCDD. She has been practicing for over 24 years and is an author of multiple DWI Defense textbooks. She is also a national and state-wide lecturer on the law.

The Coffey Firm handles a wide variety of cases, including Unlawful Carrying Weapon (UCW), Assault (including family violence), and Possession charges. We can also help you try to get a DWI off your record or avoid probation revocation. The Coffey Firm offers fair DWI payment plans and free consultations.

Mimi is also listed on several “top criminal lawyer near me” directory listings such as Wise County DWI Lawyers, Tarrant County DWI LawyerDallas County DWI attorney, Collin County DWI attorneys and Parker County DWI attorneys. Mimi is a caring DWI Lawyer in Dallas – Fort Worth. She is also involved in the Texas Tech School of Law foundation and enjoys using the skills she has developed to give back to the community.