If a person is stopped for driving under the influence of alcohol or drugs, one of the tests commonly given by police is called the horizontal gaze nystagmus. The flashing hazard lights on the police car or police car headlights can cause optokinetic nystagmus that the arresting officer will misdiagnose as horizontal gaze nystagmus.
The standard testing manual for police officers trains them in administering the horizontal gaze nystagmus test. They are also taught that the hazard lights can cause optokinetic nystagmus. Therefore, if the eye test is given while the lights are flashing, the results may not be reliable.
The lawyer who is representing the person charged with driving under the influence where the eye test was given should make sure to investigate whether or not hazard lights caused optokinetic nystagmus.