In Emerson v. State, 880 S.W.2d 759, 763 (Tex. Crim. App. 1994) the Courtdeclined to admit as a lay opinion an officer's testimony regarding appellant's intoxication. Because the officer's opinion was based on his observations while administering the horizontal gaze nystagmus (HGN) test, this Court held that the testimony could only be admissible as expert testimony under Rule 702. Id. at 763. Although the officer personally perceived the appellant's eye movements during the HGN test, we held that his observations were not considered mere lay opinion because the test is based on a scientific theory. Id. at 763.