Can the Size of Eye Change?

It is not possible to change the size of the eye by rubbing it. If you rubbed it really hard, it is possible that you created swelling. If the area is swollen, it may give the illusion of a smaller eye. If this is the case, your issue should resolve itself within a few days. Without seeing photos or performing an exam, it is difficult to give you precise advice. There are other issues which may cause swelling in your eye, and I would recommend an exam by a board certified opthamologist to rule out the possibility of anything else. Thank you and I hope this helps!

It's difficult to answer your question without seeing you or a picture.  The eye size should not change permanently.  It's possible that some swelling developed around your left eye when you rubbed it and that could cause the eye opening to appear smaller.  It that's the case, it should go back to normal after the swelling subsides.  If you are having any other symptoms with your eye, such as redness, pain, itching, or changes to your vision, I would recommend seeing an eye doctor (ophthalmologist).  

There are only two things that will make the apparent size of the eye change. First is swelling, perhaps like an irritant that caused you to rub your eye. The second is disruption of one of the stabilizing ligaments. This will cause the eye to change shape, and, thus, apparent size. Without an examination (or, at least, a very good picture) it is impossible to say what the problem is or if there even is a problem. See someone experienced in eye problems if your symptoms change or worsen or the problem does not resolve soon.