HGN Testing
Many of us in the Allen and McKinney areas have heard of the Horizontal Gaze Nystagmus test but most refer to it as the "eye test". If you have had this test performed, you have recently been suspected of driving under the influence or driving while intoxicated. Many people are unaware of the many causes of Horizontal Gaze Nystagmus beside being intoxicated. You're in luck, the following explains more about the testing process and the errors that can easily be incurred during the process.
HGN Testing
Horizontal gaze nystagmus is an involuntary jerking of the eyeball which occurs naturally as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. An alcohol-impaired person will also often have difficulty smoothly tracking a moving object. In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object, often a pen or small flashlight, horizontally with his or her eyes. The examiner looks for three indicators of impairment in each eye: if the eye cannot follow a moving object smoothly, if jerking is distinct when the eye is at maximum deviation, and if the angle of onset of jerking is within 45 degrees of center.
Testing Accuracy:
HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.The NHTSA manual says that if the FST tests are not performed properly, or if conducted without adhering to the training protocols, such actions “compromise” the validity of these evaluations.The HGN evaluation, when performed correctly on proper subjects, had a 77% “claimed” reliability rating. The Walk-and-Turn exercise, when conducted properly on a qualified subject on a dry, level surface, was found to be 68% reliable. The One-Leg-Stand exercise, when conducted properly, on a qualified subject on a level, dry surface and under proper instructions and where correctly demonstrated and scored, reportedly yields about 65% reliability. Cumulatively, if all are done correctly, up to 83% correlation to a BAC of 0.10% or more may be expected according to NHTSA. Knowledgeable DWI criminal defense lawyers know that 95% or more of the officers administering these evaluations do them wrong, or conduct them in a manner (or on a test subject) not approved by the SFST manual, or grade the evaluations improperly, as per the manual, or ALL OF THE ABOVE. When done incorrectly, these evaluations have ZERO predicted reliability.
Please consult an experienced DWI or DUI attorney to see what other defenses can be used to eliminate of minimize your charge. To learn more about Field Sobriety Tests and DWI defense contact Mr. Kyle Shaw, an experienced Plano McKinney and Allen DWI attorney at (214)726-0088.