This test can be administered with the driver sitting in their vehicle or with the driver laying in a hospital room, however it is commonly performed on the side of the road. In this instance, the officer will tell the subject to stand with their feet flat on the ground with the heels and toes touching. The subject will be instructed to stand with their hands to their sides and to remain in that position until given further instruction.
The officer will place a pointed finger or a stylus (pen or pen light) in front of the subject's face and direct the subject to follow the movement of the stylus without moving their head. The officer will then pass the stylus from left to right; up and down, in front of the subject's face. The officer is looking to see how smoothly the subject's eyes track the moving object and if there is a presence of "nystagmus," which is a bouncing or jerking of the eyes. Nystagmus is involuntary so the test subject's eyes could be jerking profoundly and they would not feel it or be aware anything is happening. Although nystagmus can be caused by a variety of factors, police officers assume it is a reliable symptom of alcohol impairment.