A Massachusetts law enforcement officer who has reason to believe a driver is impaired may make a traffic stop to evaluate the situation further. If he or she feels there is enough evidence at that point, there may be a field sobriety test, which can assist officers in identifying people who are driving under the influence. According to AAA, over 90 percent of roadside sobriety tests are successful when administered by a properly trained officer. This leaves significant room for error.

When officers require drivers to follow a moving object from side to side with their eyes, alcohol impairment will cause the eyeball to jerk. This movement is known as horizontal gaze nystagmus. While a drunk driver would not be able to maintain a steady gaze and would exhibit this telltale sign of a high blood alcohol content, many people have medical conditions that lead to the same response.

Medline Plus explains that this health problem stems from the brain, rather than the eyes, and it also involves the inner ear. So, ear conditions such as Meniere’s disease may cause nystagmus. A person with this disease may also experience dizziness. Labyrinthitis is another inner ear disorder that causes acquired involuntary eye movements.

A brain injury or stroke may cause the onset of the issue, as well as several kinds of medication. In addition to the involuntary eye movements, a person may suffer from disorders of the nervous system and vision problems. However, people who have nystagmus do not always know because they typically are not able to feel the slight tremor, and for many, it causes no other problems.