Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
I would suggest that you be seen by an ophthalmologist (an eye specialist). From the neurological perspective, abnormal pupil sizes can be caused by lesions to the third nerve – as may be the case by an aneurysm compressing the nerve. This would cause an enlarged pupil. Another cause of abnormal pupil size can be related to injury to the neck causing injury to the nerve fibers near the carotid artery. This injury may occur with a motor vehicle accident. This causes a smaller pupil.
The intermittent nature of your pupillary changes would make the above considerations less likely. There is a condition called episodic anisocoria that may be related to the intermittent spasm of the pupillary dilator muscle. Another benign condition is called hippus which is the constriction-relaxation of the pupillary muscles particularly with light.
Do you have headaches with your pupillary changes? There are headaches called cluster headaches that can cause changes in pupil size.
Again, I would suggest that you follow up with an ophthalmologist. He/she would be best at determining the cause of your pupil size changes.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
Thank you so much for that information. I did end up going to the hospital Sunday to have it checked, and saw an ophthalmologist who did a thorough exam and said that my eyes both look very healthy and couldn't see any cause for the strange pupillary changes, and also ruled out Horner's syndrome. Unfortunately it wasn't happening when I was there...
With your idea of 'episodic anisocoria' I was able to google that and found some very useful information and read about 'tadpole pupil'. I found this case study report which sounds exactly like what I have been experiencing. It sounds like my idea of a tiny muscle spasm was pretty much on track, and it was really nice to hear that I am not alone!...
The article is at http://www.nature.com/eye/journal/v18/n1/full/6700513a.html
Thank you again for your input!