Curtis Johnson wrote in a message to Roy J. Tellason:

 WC> and I'm allergic to atropine.
 CJ>  
 CJ>    Another legitimate use is for opthamologists to drop into the
 CJ> eyes to dilate the pupil.   The herb belladonna has a bit of
 CJ> atropine in it, so despite the dangers of dosage it was used 
 CJ> cosmetically to dilate the pupils, hence the name for the herb--
 CJ> "beautiful lady."

 RJT> I didn't know that was what they used to do those checks (my
 RJT> optometrist uses something of the sort,  and yes I know the difference
 RJT> between that and an opthamologist :-).  We had an appointment a while
 RJT> back where my other half got an exam and ended up with a new pair of
 RJT> glasses that she's happy with,  and that dilation was a part of it. 
 RJT> Went out for dinner later that night,  and in listening to her
 RJT> descriptions of some of the visual effects,  I connected that with
 RJT> descriptions I'd heard of some of the effects of hallucinogens. 
 RJT> Extreme pupil dilation being one of the "symptoms" of
the use of those
 RJT> drugs,  I'd never connected the visual stuff with an actual effect
 RJT> caused by the dilation until then... 

 CJ>    The reason, of course, that an opthamalogist uses the drops is 
 CJ> that such artificial dilation lets him/her shine a light in and 
 CJ> take a good look at the retina.  Not necessary for the usual 
 CJ> eyeglass testing, but a good idea to catch some nasty stuff early.

Yeah,  that's my understanding of it.

 CJ> I don't remember anything particularly hallucinogenic in connection
 CJ> with the the drops I had earlier, except it making everything 
 CJ> bright (hence the caution with light exposure), but maybe that was
 CJ> just me and the dose.

It wasn't that I was thinking of as much as the extreme dilation that I
also observed among some users of hallucinogenic drugs,  particularly back
in the late 1960s.  What I was thinking was that perhaps some of the
effects that had been attributed to the drugs were actually an artifact of
the dilation,  perhaps even caused by impurities such as atropine...

 CJ>    Drugs that do heavy numbers on the central nervous system will
 CJ> generally show that by dilation of pupils (if they're a depressant)
 CJ> or by "pinprick" contraction (if a stimulant).

I hadn't noticed that about depressants,  or read about it,  either, 
though I remember something about the stimulant effects.

 CJ> A low-tech method (to keep on topic) favored by emergency medical 
 CJ> techs to see if there's been a concussion or whatever is to prop 
 CJ> open the eyelid and shine a flashlight in and see if the pupil 
 CJ> contracts.

That,  and to see if they're different.

 CJ> Besides light, something else that affects dilation and 
 CJ> contraction of pupils is whether one sees something desirable or 
 CJ> not.  If one sees something desirable the pupil will dilate; this 
 CJ> used to be an old trick of jade dealers, and it's been used in 
 CJ> high-tech methods of various kinds.  Of course, if a woman signals 
 CJ> that she's interested by dilated pupils, a guy will likely also 
 CJ> become more interested, hence why "belladonna" got the name.

I think that there's something in the way our brains are wired to suggest
that someone who is looking at you with dilated pupils is also more
attractive...

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