Contrary to popular belief, the officer is not checking to make sure you can simply follow the pen or their finger; They are checking to see if your eyes jerk during testing. This jerking is an involuntary movement that may indicate the presence of alcohol and/or drugs in a person’s system. It can also be caused by certain medical conditions and medications.
If you are wearing glasses, the officer should have you remove them prior to testing. You should be faced away from any moving lights and passing traffic. The tests should then be administered as follows:
Lack of Smooth Pursuit
Distinct and Sustained Nystagmus at Maximum Deviation
Onset of Nystagmus Prior to 45 Degrees
Check your tests against the above procedures. If the officer did not substantially comply with the procedures, the accuracy is compromised and may be sufficient grounds to keep the tests out of evidence.
Continue on to Walk and Turn Test