Written by attorney Edgar J. Reynoso


Horizontal Gaze Nystagmus The suspect must be instructed to look straight ahead, keeping the head still while following and focusing on the stimulus with the eyes until told to stop. The stimulus must be twelve to fifteen inches in front of the suspect's eyes for ease of focus. The officer is trained to receive an acknowledgement from the suspect that the stimulus is at a comfortable distance from the suspect's eyes and to document this confirmation. Even though this test is not a vision test, per se, eyeglasses are to be removed in order for the officer to make a more accurate determination of the final total points. If the suspect can not see the stimulus after removing the eyeglasses, they must be allowed to perform it with them on. According to the manual, hard contact lenses are to be removed so as to avoid dislodging when the eyes are out at maximum deviation or to prevent damage to the eyes. A person with a glass eye or only vision in one eye can not be given this test for evaluation of just one eye and then a subsequent doubling of the score, assuming that the other eye will render the same results, is both erroneous and improper. If the suspect has what is known as the lazy eye condition, the officer is trained to test one eye while the other eye is covered by the suspects’ hand, then to switch same. A person who is color blind is not validated for this test as they will probably have a pathological Nystagmus which is normal and natural for that condition. This can be caused by some type of neurological disorder, brain damage, epilepsy or pathological disorder which the suspect is born with or of unknown etiology. A large disparity between the right and left eye can clue the officer into this problem. At an accident scene, if the suspect sustains a concussion, this may bring on a pathological Nystagmus thereby invalidating this test. Although very few test conditions affect gaze Nystagmus, there are certain administrative procedures that must be followed. As previously mentioned, the stimulus must be placed twelve to fifteen inches in front of the suspect's eyes. The stimulus should be held above eye level, so that the eyes are wide open and looking directly at it. Due to narrowness of certain individuals’ eyes it becomes more difficult to make a fair evaluation of the Nystagmus unless the eyes are wide open. If the officer believes that the Nystagmus might be there, it can not be scored, as the benefit of the doubt must be given to the person that is being tested. The officer is also trained to administer this test with the suspect looking into a quiet background, facing away from police cruisers and oncoming traffic. This is to avoid the probability of evaluating an induced condition known as optokinetic Nystagmus, which develops when a person focuses on several objects at one time or on objects that are moving away. This optokinetic Nystagmus is a defense mechanism of the body in order to keep the eyes from tiring. There are numerous visual or other distractions that may also impede this test. Certain environmental factors such as wind and dust may interfere with the performance of the Nystagmus test. When administered alone, Horizontal Gaze Nystagmus is considered to be 77% accurate by the law enforcement community. First Clue: Lack of Smooth Pursuit As explained earlier, Nystagmus is the involuntary jerking of the eyes. With alcohol intoxication, three clues will be sought after, the first of which is smooth pursuit. The officer is trained to look for the suspect's inability to pursue a stimulus smoothly moving horizontally while focusing on that. If the suspect moves his head to the side at any time, the score may be invalid regardless of which clue the officer is looking for. An example of smooth pursuit is a marble rolling across a smooth pane of glass: this would be a very smooth pursuit. If the suspect is under the influence, the eyes will bounce or jerk in similar fashion, as if that same marble was rolled across a piece of sandpaper. The officer is instructed to check the left eye first by moving the object to the officer's right. The object must be moved smoothly in order to comfortably bring the suspect's eye as far to the side as it can go. Any choppy or shaky hand movements or movement that is too fast by the officer may induce a Nystagmus in the suspect's eyes and invalidate the test. The officer is instructed to make two or more passes in front of the eye to be absolutely certain that there is a Nystagmus. If this clue is scored as Nystagmus the suspect is assessed one point. However, if the suspect has this clue emanating in one eye, it is not guaranteed that it will be exhibited in the other eye. Second Clue: Distinct Jerkiness at Maximum Deviation After the officer has checked the first eye for the smooth pursuit clue, the same eye must be checked for distinct jerkiness at maximum deviation. This is accomplished by simply moving the object to the side until the eye has gone as far to the side as possible. At maximum deviation, no sclera or “white" will be showing in the corner of the eyeball. The officer must hold the eyeball at that position for two or three seconds and attempt to discern distinct eyeball jerkiness. If the officer can not make this distinction from a slight Nystagmus, the benefit of the doubt must be given the suspect. The officer may make the mistake of not bringing the eyes out to side as far as they can go or too rapidly returning the stimulus and incorrectly score this part of the test. During the test, a certain degree of uncomfortableness is experienced, causing a slight twitching of the eyes at maximum deviation and if the officer returns the stimulus too quickly, the natural Nystagmus may be mistaken for that caused by intoxication. Final Clue: Angle of Onset Although the most difficult to evaluate, the angle of onset is perhaps the greatest indicator of the presence of the other clues. This correlation, however, does not work conversely. The presence of either of the first two clues does not guarantee that the third clue will be present. The person is told to follow the stimulus until they are looking down a 45-degree diagonal. In order to estimate the 45-degree angle, the officer is told to place the stimulus halfway between the suspect's ear and nose on the side being tested or just outside the shoulder area. The estimation of this angle is critical, since studies have shown that as the alcohol increases, the angle will decrease. Although this may be the case, this angle should not be used to estimate a specific amount of alcohol in the bloodstream. To score this part of the test, the officer must move the object to a 45-degree angle so the eye matches this angle, looking for jerkiness in the movement. If Nystagmus is observed, the stimulus is stopped and the officer must make note a continued jerkiness. If it does continue, the officer must observe whether there is still white showing in the corner of the eye and then the angle is noted as prior than 45-degrees. If there is no jerkiness, the stimulus must continue to be moved until the jerking occurs or the 45-degree angle is reached. If no white of the eye is showing, the eye has either been taken too far to the right, which would indicate maximum deviation, or the person has unusual eyes that will not deviate very far to the side. The criterion of onset before 45-degrees only can be used if some white can still be seen at the outside of the eye, however, too often the officer incorrectly estimates the angle or scores this with no white showing in the corner of the eye or both. This test is deemed the most reliable test in determining probable cause to believe someone is under the influence of an alcoholic beverage; however this obviously depends on whether the officer adheres to the proper administration and proper scoring of the test. This test should not be administered if the suspect is lying down but can be administered to them if they are sitting or standing.

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