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Attacking HGN Tests | Chicago DUI Lawyer

All of the Field Sobriety Tests provide numerous opportunities for officer error in administering the test and in interpreting its results and for your Illinois DUI Defense Lawyer to attack the supposed validity of your "failing" HGN Test results. The Horizontal Gaze Nystagmus (HGN) Test is no exception. It requires the test subject (you) to follow a stimulus with your eye as the officer moves it from side to side. The stimulus on a roadside Field Sobriety Test is usually something like the officer's pocket flashlight.
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Attacking HGN Tests

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Illinois DUI Defense Lawyer Attacking Your HGN Test Results

All of the Field Sobriety Tests provide numerous opportunities for officer error in administering the test and in interpreting its results and for your Illinois DUI Defense Lawyer to attack the supposed validity of your "failing" HGN Test results. The Horizontal Gaze Nystagmus (HGN) Test is no exception. It requires the test subject (you) to follow a stimulus with your eye as the officer moves it from side to side. The stimulus on a roadside Field Sobriety Test is usually something like the officer's pocket flashlight.

Illinois DUI Defense Lawyers understand that the concept behind the HGN Test postulates that the presence of a central nervous system depressant like alcohol will affect your eye pupil size, your ability to smoothly track objects like the stimulus with your eye, and your ability to control the muscles that control your eye's movements. Through this HGN Field Sobriety Test, the officer tries to evaluate your pupil size, tracking, smooth pursuit, and “distinct” nystagmus at "maximum deviation” to determine whether your driving is impaired by alcohol. This is no simple or straightforward task.

The test procedures follow this pattern:

  • The stimulus should be held 12 to 15 inches away from the eye.
  • The officer should move the stimulus from left to right and then right to left for each eye. Twice.
  • The officer must use at least 2 seconds to move the beam from the center position to the side (the point of maximum deviation).
  • He should hold the beam at the point of maximum deviation for at least 4 seconds.
  • Then he should return the stimulus to the center point of the eye, taking at least 2 seconds again.
  • He should repeat the whole process twice for each eye.
  • He should move the stimulus in a straight line across, not allowing it to loop, curve, or distract.

The crucial issue in a Field Sobriety Test is whether that test was administered and interpreted while precisely following the NHTSA (National Highway Traffic Safety Administration) guidelines for the test. One research study concluded that officers administer Field Sobriety Tests incorrectly more than 90% of the time.

The NHTSA training manual warns that the standardized Field Sobriety Tests like the HGN Test are not flexible. At all. In order to have any value at all as evidence, Illinois DUI Defense Lawyers insist that Field Sobriety Tests be administered each time exactly as prescribed by the NHTSA. Officers must not deviate from the NHTSA instructions in any way. The NHTSA manual cautions that the HGN Field Sobriety Test results could only to be considered valid indicators of your blood alcohol concentration (BAC) level when:

  • The test is administered in the prescribed, standardized manner in exact compliance with NHTSA guidelines;
  • The standardized NHTSA designated "clues" regarding alcohol impairment are used to assess the subject’s performance; and
  • The standardized NHTSA criteria are employed to interpret your performance on the HGN Test.

If even one of the standardized test elements is changed or improperly administered or interpreted, the validity of the test as a reliable indicator of your BAC level is ruined.

The validity of any results obtained in this phase is totally dependent on the officer’s ability to administer the test perfectly and without even the smallest deviation from NHTSA guidelines. The NHTSA requires that the stimulus be moved at a speed that takes at least 2 seconds from the center position to the point of maximum deviation. Under uncontrolled roadside field conditions, the officer must make a best guess regarding speed and timing.He must simultaneously attempt to evaluate the suspect’s performance.

Attacking the HGN Test and Creating Reasonable Doubt about Your Guilt on the DUI Charge

The prosecution must prove your guilt beyond a reasonable doubt in order for you to be convicted on a DUI Charge. Even where your arresting officer claims that you "failed" the HGN Test, your Chicago DUI Attorney could raise several issues that could create reasonable doubt about your intoxication:

  • The HGN Test was not administered correctly;
  • There are many other conditions that can interfere with accurate HGN Test results;
  • The arresting officer was not properly qualified to conduct the HGN ophthalmologic test;
  • The arresting officer did not distinguish intoxication-based nystagmus from natural nystagmus;
  • The arresting officer did not properly distinguish "maximum deviation" in the HGN Test; or
  • The officer failed to give other recommended Field Sobriety Tests in addition to the HGN Test.

Attacking Improper Administration of the HGN Test by Your Arresting Officer

As mentioned previously, the HGN Test must be given correctly in order to have any value as evidence. Under the NHTSA guidelines,at least 25 different steps must be performed to properly conduct the HGN Test.These procedures must be followed with precision and failure to do so renders the results inaccurate and unreliable.

There are several common mistakes that officers tend to make in the field in administration of the roadside HGN Field Sobriety Test that your Chicago DUI Attorney could attack on cross-examination at your trial:

  • The officer might have moved the stimulus too quickly or too slowly on individual passes across your eye;
  • The officer might have held the stimulus too close to your eye or further away  than the NHTSA requires;
  • The officer might not hold the stimulus for at least 4 seconds at the point of “maximum deviation” when looking for the presence of “distinct nystagmus” or he might hold it there too long (which increases nystagmus); and/or
  • The officer might not be able to hold the stimulus in a steady line as he moves it across your eye.

There are Many other Causes of Nystagmus besides Intoxication. These can Affect Your HGN Test Results.

There are eye disorders, neural disorders, and other conditions that can cause nystagmus and affect your HGN Test results. They can cause you to "fail" an HGN Test even when you haven't had a single drink. Among the conditions that can affect your HGN Test results are:

  • Wernicke's encephalopathy
  • Heatstroke
  • Influenza
  • Arteriosclerosis
  • Some other illnesses
  • Hypertension
  • Vertigo
  • Fatigue
  • Eyestrain or eye muscle fatigue
  • Aspirin
  • Caffeine
  • Nicotine
  • Prescription drugs such as blood pressure medication

Your Chicago DUI Attorney could demonstrate through careful questioning on cross-examination at your trial that the arresting officer was no expert in the science behind the HGN Test. Your Chicago DUI Attorney could ask whether the officer had special training to detect neural or eye disorders,whether he asked you if you have any neural or eye disorders, and whether he consulted your medical records to determine if you had any neural or eye disorders.

Your Chicago DUI Attorney Could Attack the Arresting Officer's Qualifications to Conduct the HGN Test, which is an Ophthalmologic Examination

The HGN Test is basically an ophthalmologic examination that tests a person's eye movements. Nearsighted and farsighted folks who get regular ophthalmologic exams have no doubt taken the test several times and might be familiar with the essential procedure.


You cover (or in a Field Sobriety Test context close) one eye. You focus your other eye on a little beam of light from the examiner's special testing instrument. This is the "stimulus" and in the case of your arresting officer might have been a pocket flashlight.


As your eye follows the light beam stimulus during the test,your eye will begin to exhibit some nystagmus (involuntary oscillations) as the beam reaches a deviation of 40 degrees or more from the center point. In an intoxicated person or a person affected b y prescription drugs or some other neural and eye conditions, that nystagmus reaction will occur before the 40-degree mark.


But the HGN Test is an ophthalmologic examination that requires some experience and training in order for the tester to be able to determine the cause of the nystagmus and whether it is natural to the test subject or the product of additional influences like alcohol. Your arresting officer is trained to look for signs of intoxication thorough the HGN Test, so that is the factor to which he will attribute your signs of nystagmus. An actual trained ophthalmologist has learned to look for the other potential eye or neural disorders first. The HGN Test is biased when administered by an unqualified individual that is not an ophthalmologist.

Thorough questioning of the arresting officer on cross-examination could make him admit that:

  • The HGN Test is actually an ophthalmologic examination, not just a simple Field Sobriety Test;
  • The officer is not, in fact, an ophthalmologist;
  • The officer has taken no courses in ophthalmology or had any special training in ophthalmology; and
  • The officer has no degree in ophthalmology.

Your Chicago DUI Attorney could create reasonable doubt about the value of your HGN Test results in relation to the DUI Charge by carefully demonstrating that the officer was not really qualified either to administer the HGN ophthalmologic exam or to interpret its results.

The All Important Tasks of Distinguishing Distinct Nystagmus and Maximum Deviation

During your HGN Test, the officer will attempt to make the highly technical determination of whether you demonstrate "distinct"nystagmus at some point of your eye's maximum deviation from the center resting point of the eye. Nystagmus is the involuntary oscillation of the eye in response to a loss of muscle control. Many other things than alcohol's depressant effect on the central nervous system can cause it. Heat stroke victims often display nystagmus to a high degree.

People with the condition called "lazy eye" often display a highly visible form of nystagmus. But nystagmus to some degree is present naturally in all individuals, especially at the point of the eye's maximum deviation. Maximum deviation is a difficult position for the eye's muscles to hold. And nearsighted and farsighted persons with variable eye muscle tension might be more prone to nystagmus at maximum deviation.

Maximum deviation is the point at which the eye has moved fully to one side and cannot move any farther. The officer must attempt the complex and technical tasks of distinguishing whether your eye's oscillations are “distinct” nystagmus or natural nystagmus and then accurately identifying your eye's point of maximum deviation.

Different individuals naturally have greater or less maximum deviation and peripheral vision. And determining whether your nystagmus is a natural condition or caused by alcohol's depressant effect on the central nervous system presents a real technical challenge.

As your Chicago DUI Attorney realizes, the HGN Test is held by officers to be a scientific and objective test of your level of intoxication. But the HGN Test is deeply flawed for two reasons:

The administration of the test cannot be effectively controlled or standardized when performed under field conditions like a busy roadside at night; and

The results that the HGN Test produces in the field under the administration of an officer not specifically qualified to give ophthalmologic tests are fully subjective products of the varying perceptions and interpretations of various law enforcement officers and their expectations.They expect to see nystagmus caused by alcohol consumption; therefore they willsee it.

The HGN Test, if Administered Perfectly, is Still only Accurate on About 3 out of 4 Tests

Even with an accuracy rate of only around three out of our tests, the HGN Test is regarded as the most accurate Field Sobriety Test.But even when administered accurately by officers, the HGN Test gives only a 77% accuracy rate. That means that out of every 100 HGN Tests given, 23 of them remain inaccurate.

A U.S. DOT (Department of Transportation) report called Improved Sobriety Testing acknowledges the poor accuracy rate by stating that where an HGN Test indicates a driver might be impaired by alcohol, the officer should also administer the other two standardized tests to provide more firm data on which to base a DUI arrest. The other two tests standardized by the NHTSA are the One Leg Stand Test and the Walk and Turn Test.

If an officer arrested you because you "failed"the HGN Test, your Chicago DUI Attorney should question whether the other two standardized tests were also given to you. If not, your Chicago DUI Attorney could point out that the officer failed to abide by the accepted procedure detailed by the U.S. DOT. Without the other two test results, your officer could not, under U.S. DOT guidance, have firm data to support your DUI arrest.Your Chicago DUI Attorney could also reiterate that the HGN test is accurate only about 77% of the time.

Contact Experienced Illinois DUI Defense Lawyer Michael P. Schmiege to Successfully Defend You from a DUI Charge based on a"Failing" HGN Test Result

Your DUI trial is your one chance to attack the prosecution's case against you and escape conviction on the DUI Charge. To do that, you need the skill, knowledge, and experience of an effective Illinois DUI Defense Lawyer like Michael Schmiege on your side.

Hire aggressive and effective Illinois DUI Defense Lawyer Michael P. Schmiege to take your case to trial and to cross-examine the officer that arrested you. Michael Schmiege's skilled cross-examination of your arresting officer could reveal that he improperly administered and evaluated your HGN Test and that the test results are therefore inaccurate. This tactic could create the reasonable doubt that you need to avoid conviction on the DUI Charge.

Contact Illinois DUI Defense Lawyer Michael Schmiege today for a free case evaluation consultation. Let him help you understand your legal options. Michael P. Schmiege's aggressive advocacy could safeguard your right sand provide your key to freedom after a DUI charge based on an improperly administered HGN Field Sobriety Test. (312) 906-7800

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