Causes of pupil dialation?

Hello :)

We have recently be noticing that my pupils are rather dialated much of the time. I have very fair blue eyes (not sure if that makes any difference, but i read somewhere that blue eyes are much more sensitive to light). I have not been taking any medication or anything of the sort.

We first noticed a slight abormalty about 2 years ago when i would go to the chiropractor, my eyes would be extremely dialated, whether outdoors in bright light or indoors. But i stopped going to the chiropractor and didn't really pay much attention afterwards.

Now after having my school pictures taken, we noticed how dialated they were. They were taken in a fairly lit room and it was my second take with the flash. Logic would show that they should be small, but instead they were so large that you couldn't tell what color my iris are....

So, what are some possibilities? and if this is a defect, what are some possible "cures" my doctor will suggest (i am planning a eye doc visit next week)

Other than being sensitive to light, i have never really notice any problem...

Thanks :D