DWI Information
If the officer moved the penlight in front of your face and asked you to follow it with your eyes, this is the "horizontal gaze nystagmus" test, a relatively recent development in DUI investigation. The officer attempts to estimate the angle at which the eye begins to jerk ("nystagmus" is medical jargon for eye jerking); if this occurs sooner than 45 degrees, it theoretically indicates an excessive blood-alcohol concentration. The smoothness of the eye's tracking the penlight (or finger or pencil) is also a factor, as is the jerking when the eye is as far to the side as it can go.

DWI Answers
The traditional offense is "driving under the influence of alcohol" (DUI) or, in some states, "driving while intoxicated" (DWI). In recent years, however, 43 states have also enacted a second, so-called "per se" offense: driving with an excessive blood-alcohol concentration (either .08% or .10%). In those states, BOTH offenses are charged. The defendant can even be convicted of both, but can be punished for only one.

If the case involves a refusal to submit to chemical testing, of course, only the traditional offense will be charged.