When adrenaline is released into a humans body (through the flight or fight issue, or on a roller coaster, or anything), your heart rate rises, your blood pressure increases, your eyes dialate, etc.

So yes, when adrenaline is released into your system your pupils will dialate, the downside of the dialation is that you lose some depth perception.

That's why during the Police Academy we trained extensivly to be able to "relax" during a fight or flight high adrenaline situation, so we can control our breathing, our heartrate, and restrict our pupils to more normal levels.

You're not as good of a shot with dialated pupils and a high heart rate. =]

Nor do you make nearly as good of decisions.