What is the purpose of the follow the penlight with the eyes test?
This is the horizontal gaze nystagmus (HGN) test. When conducting this test, the officer is watching for an involuntary jerking of the eye, which may, among other causes, by caused by consumption of alcohol. If the officer detects three clues in each eye, lack of smooth pursuit, nystagmus at maximum deviation, and nystagmus prior to 45 degrees, then he is trained to arrest. In Maryland, the legal effect of this test has pretty much been neutralized by two appellate decisions holding that the court can only accept the test to show the defendant had consumed alcohol.
