Eye Rubbing

Mira has been doing this a lot lately. Yesterday for instance, we went out to the park for about 30 minutes or so and she was fine for the first 15 minutes, then proceeded to do this for the last 15 minutes. She has been doing it indoors (sometimes), outdoors (very often), at school, at home, when its sunny, when it's overcast and cloudy - it doesn't seem to make a whole lot of difference how bright it is. She doesn't do it in her room a ton and yesterday it was much brighter inside than it was out in the park. Her teacher had to put sunglasses on her in the class, since she was rubbing her eyes raw this week at school.

I suppose we could chalk it up to allergies and try giving her a Claritin, but she seems to do it much more when she is outside, which leads me to believe it's the contrast with the sun. Sometimes it is an immediate reaction when we step outside the door and she won't stop until we go back in. Any thoughts?