Random One Eye Dialation

Over the past month my left pupil has enlarged at least twice the size of the right one.   This only occurs every once and a while and only lasts maybe an hour.  This has only happened three times in about a month.  There is no pain associated with this.  What might be some reasons?  It is only the dialation nothing else out of the ordinary.  

[John C Hagan III, MD, FACS, FAAO]

Next time it happens take a picture of it without flash, without redeye feature and looking off in a distance (someone will need to do this for you).

If possible see a neuro-ophthalmologist.

If you wear contacts that can cause it as can use of allergy drops, Visine, Murine and some other substances.

JCH III MD