My little frog's pupils are always narrower than my large frog's no matter the amount of light. The little one also often misses insects or doesn't strike at all.
I'm wondering if this might have something to do with eyes, or is it just an insignificant difference? (Edit: Or maybe the big frog's eyes are more dilated because he's excited whenever he thinks I'm going to feed him. He's more focused on food than the other.)
The picture is a bad example because the light was bright in this one so they both have narrow eyes, but here they are: