The Horizontal Gaze Nystagmus test – also known as the eye test or finger test – is considered the most reliable of the Standardized Field Sobriety Tests conducted on the roadside to determine whether a driver is impaired. If you’ve been stopped for a DWI in North Carolina, call (919) 352-9411.
The HGN is not a sight test. It does not measure how well you can see. It merely measures whether there are involuntary movements or twitching (nystagmus) in the eye as it moves from left to right and up and down. These two types of nystagmus – horizontal and vertical – occur for a variety of reasons. One of the reasons they occur is because the person is impaired.
The problem with the HGN test is that first it is many times not administered properly. If the person is tested in front of flashing police lights, or if the person is tested while seated in their car with their head twisted, the results will not be accurate.
In addition, nystagmus can be caused by different medical conditions that are unrelated to whether the person has been drinking. For instance, if the person has suffered from head trauma in the past, or has consumed significant quantities of caffeine, the person may show nystagmus (or twitching) without actually being impaired.
For this reason, while HGN is considered a very reliable SFST, it can be more easily shown to be faulty in court under the right questioning by a Raleigh criminal lawyer.