The Horizonal Gaze Nystagmus test is unique among the three approved Field Sobriety Tests. The other two FSTs are divided attention tests which measure both mental clarity and physical dexterity. The HGN test, on the other hand, has nothing to do with either of these things.
Most people have experience with this test, even if they have never been pulled over for DWI. The test administrator, which in this case is a police officer, has the subject track a moving object by simply moving his/her eyes. If the pupil moves involuntarily at certain angles, the subject probably has nystagmus.
What Causes Nystagmus?
Typically, nystagmus is a medical condition as opposed to an environmental condition. In other words, alcohol usually has nothing to do with this condition. The major types are:
· Spasmus Nutans: Between ages six months and three years, many children have difficulty controlling their eyes. These children may also tilt and nod their heads quite frequently. For the most part, this type of nystagmus usually goes away on its own. However, the residual effects may linger for decades.
· Infantile: This type of nystagmus is even more common and develops even earlier, in children as young as two or three months old. Although it usually lasts a lifetime, unless the person is fatigued or under stress, infantile nystagmus is barely noticeable.
· Acquired: Alcohol can cause nystagmus in adults. Then again, so can inner ear infections, extreme nearsightedness, astigmatism, certain medications, and a number of other things. Other times, acquired nystagmus simply happens without any discernable reason.
During cross-examination, attorneys often ask officers if they screened the defendant for spasmus nutans or infantile nystagmus. The answer to that question is almost always "no," and that response often creates reasonable doubt as to the test's accuracy in this context.
Challenging the Test Results
If the HGN test occurs under controlled conditions, it is about 80 percent effective. Since so many things other than alcohol can cause nystagmus, that figure is borderline convincing in criminal cases.
But roadside HGN tests do not take place under controlled conditions. Most DWI stops occur at night. The officer usually uses a very bright "takedown" light to illuminate the scene, and overhead lights flash in the near distance. Moreover, a DWI arrest is an extremely stressful situation. So, any latent nystagmus is likely to come out.
Finally, the officers are usually only borderline qualified to conduct the test. Typically, everything they know about nystagmus comes from police-sponsored education seminars. In fact, many officers may not even know what spasmus nutans and infantile nystagmus are. Arguably, that lack of knowledge affects their ability to interpret the test results.
The HGN test is simply not a reliable indicator of intoxication or sobriety. For a free consultation with an experienced criminal defense attorney in Fort Worth, contact Herreth Law. We have several offices in the Tarrant County/Parker County area.