Interviewer: What’s the purpose behind the Horizontal Gaze Nystagmus test? Is there really a scientific basis behind that one.
Fred Dry: There is a scientific basis to all of these tests but only if each one is administered correctly. They have around an 80% – 90% reliability factor. That is to say, up to 1/5th of the time they are just dead wrong, even when they are done perfectly. Nystagmus tests are not based upon physical performance that you generate volitionally. It tests the movements of your eyes and it’s a technical test. There are 3 factors: 1) whether or not your eyes will track smoothly, 2) do the eyes begin to jerk (onset of nystagmus) before or after reaching a 45 degree angle and, 3) is the nystagmus distinct at maximum deviation. The police officer has either some type of pen or pencil or a flashlight that they move across or up and down in front of your face. They’ll be watching your eyes to see if they track together; do they follow smoothly, and that there’s no jerkiness.
The Nystagmus is a Technical Term Used for Jerkiness of the Eyes During Horizontal Movement
The Nystagmus is officially another word for jerkiness and they are also looking to see where it will begin as your eyes travel from one side to the other and how distinct it is when your eyes get to the maximum sideward deviation. There are factors; one of which is that the officer has to make a determination whether or not the nystagmus will begin before or after a deviation of 45 degrees. He has to make an accurate determination of when your eyes reach 45 degrees. We’re talking about the side of the road, we’re not talking about a laboratory setting. In my estimation it is difficult to do this particular test reliably and correctly in that circumstance.
Even when the Nystagmus test is Performed Correctly there is a Substantial Error Rate
Some of the authorities believe that, when done properly, this is a reliable test. But even with that reliability there’s a substantial error rate. If it is video recorded, the court can see how it was administered and that there were instructions from the officer on how to take it. How quickly to move the stimulus? How near or far it should be from the face? There are rules about how it’s supposed to be done. As with all of these things, they’re often times done in a defective way.
Other Factors that May Cause Nystagmus in a Subject Performing the FSTs
Interviewer: Are there any other factors that would cause the eye to do that as well.
Fred Dry: There are medical conditions, there are eye conditions that cause people’s eyes to do that. Head injuries, neurologic disorders, prosthetic eyes, brain tumors or inner ear diseases are conditions other than intoxication which can cause nystagmus to occur.
An Overview of the One Foot Balance Test in the State of Illinois
Interviewer: What does the one-foot balance one consist of? What is the purpose of that and what are police office officer looking for?
Fred Dry: It’s a similar test to the walk and turn in terms of what they are looking for. It’s also known as the one leg stand. It’s testing your ability to balance, you’re required to stand on one foot. It could be either foot of the person’s choosing and you raise the other foot off the ground about a foot and you’re expected to look down towards your feet while you do this. You’re instructed to count. Some police officers have you count like a football player one one thousand, two one thousand up to thirty. Sometimes they time it with a stopwatch, sometimes they will count. But often times they will have you count because they want another divided attention test where you are required to do something mentally while you doing something physically. You’re supposed to keep the elevated leg in the air for the full count.
This Particular Test Cannot be Performed if the Subject has Physical Defects or Obesity
You’re not supposed to hop or skip or put your foot down. Also you’re supposed to keep your hands at your sides while you do this and not raise them. This is another situation where they say keep your hands at your sides but they don’t always say don’t raise them and then mark you down if you do. It’s not an easy test, if you have problems with your legs or your hips or your back or you’re 50 pounds overweight or you’re 65 or more years of age they are not considered valid. These tests are not as reliable for people with these issues as they are for other people. Police still use them. So they are also factors that your lawyer should bring up as well as the manner in which you’re instructed and where you’re taking the test. If it’s well-lit, whether the pavement is flat and level, if it’s wet or if it’s raining or if you’re doing it in a place where you perceive danger or you’re facing into the headlights of oncoming traffic. These are all factors which can be brought up and do have an effect on the reliance that is placed on the test.