What Is the HGN Test ?
When administering the HGN test, a law enforcement officer is trained to look for three "clues" in each eye.
Nystagmus is an involuntary, rapid, rhythmic movement of the eyeball that is exaggerated through the use of alcohol and certain other drugs; identification of four out of six clues serves as a reliable indicator of intoxication and can be used by the officer in determining whether to make an arrest. Compton v. State, 120 S.W.3d 375, 377 (Tex. App.--Texarkana 2003, pet. ref'd).
In Emerson v. State. 880 S.W.2d 759, 768 (Tex. Crim. App. 1994), the court concluded that the theory underlying the HGN test and the technique employed in administering it were both sufficiently reliable to allow the test to be admissible under evidence rule 702. Id.; see also TEX. R. EVID. 702.
In each individual case, however, the State still must show by expert testimony that the test was properly administered. See Emerson, 880 S.W.2d at 769.
Accordingly, the results from the administration of the HGN test may be admitted at trial under the following circumstances:
(1) the testifying officer qualifies as an expert witness regarding the test's administration and technique;
(2) the officer administers the test properly;
(3) the results are not inadmissible for some other reason. Ellis v. State, 86 S.W.3d 759, 760 (Tex. App.--Waco 2002, pet. ref'd) (citing Emerson, 880 S.W.2d at 763, 769).