Is the Horizontal Gaze Nystagmus or eye twitching test the most scientific test? Yes, if done by a medical doctor in a dark room by not by a Police Officer on a busy freeway.  Nystagmus simply means a jerking of the eye due to disequilibrium.  Nystagmus may be caused by over 43 other factors. In State v. Witte, 251 Kan. 313, 326, 836 P.2d 1110, 1119 (1992), the Court wrote:

Nystagmus can be caused by problems in an individual's inner ear labyrinth. In fact, irrigating the ears with warm water or cold water...is a source of error. Physiological problems such as certain kinds of diseases may also result in gaze nystagmus. Influenza, streptococcus infections, vertigo, measles, syphilis, arteriosclerosis, muscular dystrophy, multiple sclerosis, Korsakoff's Syndrome, brain hemorrhage, epilepsy, and other psychogenic disorders all have been shown to cause nystagmus. Furthermore, conditions such as hypertension, motion sickness, sunstroke, eyestrain, eye muscle fatigue, glaucoma, and changes in atmospheric pressure may result in gaze nystagmus. The consumption of common substances such as caffeine, nicotine, or aspirin also lead to nystagmus almost identical to that caused by alcohol consumption. (Quoting Pangman, Horizontal Gaze Nystagmus: Voodoo Science, 2 DWI J. 1, 3-4 [1987])

Further, Head Injuries, diseases, strobe lights, and sudden changes  in temperature just to name a few.   There are 3 clues which involve a number of passes each.   Each pass requires certain timing elements.  For Example, the nystagmus at maximum deviation the stimulus must be held a maximum deviation for a minimum of 4 seconds and nystagmus be both present and sustained well after 4 seconds because even sober people exhibit nystagmus prior to four seconds at maximum deviation.  The final pass must be done so slowly that it takes 4 seconds to reach 45 degrees which is usually the shoulder or as far over as the stimulus is from the persons face (13 inches out then 13 inches over etc).  45 degrees is supposed to equal 0.08 grams of alcohol in a persons blood so no nystagmus prior to 45 degrees equals under the limit.  However if the Officer holds the pen 6 inches out from the eye then 45 degrees is only 6 inches over or just past the ear.  Can you see how this test is easy to mess up? 

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