Yes. Under Washington's DUI law - RCW 46.61.502
- the State can obtain a conviction if they can show that the person was "under the influence of" or drove while “affected by” alcohol. They do not need to prove a specific blood alcohol content level.
The Horizontal Gaze Nystagmus (HGN) test is one of the recognized field sobriety tests which is sufficient to demonstrate being affected by alcohol. The test must be administered properly. But it by itself is sufficient evidence to obtain a conviction.
However, this does not mean that the HGN test can not be contradicted by other evidence. The jerking of the eyeball (nystagmus) can be caused by many things other than intoxication
. Nystagmus can also be caused by head injuries, rotation of the body, temperature differences from one ear to the other, a foreign fluid in the blood, objects moving into and out of sight, traffic driving by, strobe lights, tired eyes, brain tumors, brain damage, and inner ear disorders, to name a few. So in any DUI prosecution the defendant can introduce evidence that the nystagmus was caused by one of these other factors and not because of intoxication. It would then be up to the court
or jury to determine which evidence is more credible.
I hope this answers your question.