Dave,

pupil reaction time is considered and studied, but I think it has not been found to be a reliable indicator for this reason:

Unlike the alcohol in blood level (how much is normal without voluntary alcohol intake is known and is very similar between person), there is a large interpersonal variance of the normal level of pupil reaction time. It varies with age, time of the day etc.

What they consistently find is that the pupil reaction time increases with a lot of substances (and states like sleepiness) know to impair driving ability. So far so good. But how are they to know which your personal pupil reaction time under normal conditions would be? My normal pupil reaction time could be larger than someone else's impaired.

So I think at this time the consensus is that pupilometry is a good indicator and a promising idea but a blood test should be made even after a failure of the pupil test.

But I'm not an expert here and I also would appreciate any input from someone knowing this field.

Wolfgang