It is not safe for you get dilated eyes while breastfeeding. Usually the dilated eyes may be caused from the sudden shock or surprise. They may even be caused by the great pressure and disorder life. You should go to the hospital to have a check to see whether you are tired these days.
Well, as a matter of fact, our eyes will automatically dilate when we face a few situations, such as panic or being frightened by something, or excited by something. So, generally speaking, our eyes would not dilate, unless we have got some serious diseases. Maybe it is just because you get into a darker place, because that could make your eyes dilate a little. But if you constantly find your eyes dilate, then it becomes necessary for you to see a doctor.
Natural Cause of Pupil Dilation is light which actually not your case, is for you, I have to say that breastfeeding closely related to arousal. So the reason for you may be excitement. Everyone knows that breast is a very sensitive part of human beings especially woman. So it's easily to get excited which make your eyes dilated.