Horizontal Gaze Nystagmus (HGN) Test Rock Hill DUI Attorney

If you have been arrested for a DUI then you have probably been subjected to the DUI Eye Test, more commonly known as the Horizontal Gaze Nystagmus (HGN). This test is actually one of three (3) standardized tests recognized by the National Highway Transportation Safety Administration (NHTSA). If properly admistered, many police departments swear by the results and often take the position no other testing is necessary. Nystagmus is an “involuntary jerking” of the eyes which officers claim cannot be “faked” by those individuals who have been drinking or using certain types of drugs. Of course, even NHTSA research has concluded this test is only accurate to a limited degree in the best of conditions. In this article, we show other possible, non-impaired, reasons why some people will have HGN without any relation to alcohol consumption.

In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object such as 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. If, between the two eyes, four or more clues appear, the suspect likely has a BAC of 0.08 or greater. As you’re probably thinking right now, this test is far from being scientifically accurate. As you also guessed, there are many reasons other than alcohol that are medically known to cause this jerk. Many of these medical conditions are listed below. Do any of these apply to you?

  1. inner ear infection or condition
  2. irrigating ears with warm or cold water
  3. influenza
  4. streptococcus infection
  5. natural or induced vertigo
  6. measles
  7. syphilis
  8. arteriosclerosis
  9. muscular dystrophy
  10. multiple sclerosis
  11. Korchaff’s syndrome
  12. brain hemorrhage
  13. epilepsy
  14. hypertension
  15. motion sickness
  16. sunstroke
  17. eye strain
  18. eye muscle fatigue
  19. glaucoma
  20. atmospheric pressure changes
  21. excessive caffeine
  22. excessive nicotine
  23. aspirin usage
  24. circadian rhythm changes
  25. acute head trauma
  26. chronic head trauma
  27. certain prescription drugs, tranquilizers, pain medications
  28. barbiturates
  29. neural disorders of the vestibular apparatus and brain stem
  30. cerebellum dysfunction
  31. heredity
  32. diet
  33. toxins
  34. exposure to solvents, PCBs, dry cleaning fumes, carbon monoxide
  35. extreme chilling
  36. eye muscle imbalance
  37. certain lesions
  38. continuous movement of the visual field past the eyes
  39. antihistamine use

As you can now see, there are many reasons for HGN in persons without having consumed any alcohol. There are also improper testing reasons for a false HGN finding that we will show in a subsequent posting. For now, just know that a DUI suspect who “fails” HGN testing may have a number of valid and persuassive defenses at their disposal. And, HGN testing is just one of many factors which can be challenged in a DUI arrest.

Be Safe. Get Home.