It depends. They both contract, but if the second pupil is small, it doesn’t matter. I have a small one, and it just causes uveitis every once in a while. I went half my life without even noticing it.
You can become sensitive to light, and the irritation can slowly cause blindness. That’s pretty much it
One fun thing: if you ever get uveitis, wearing an eye patch won’t work. Your eye will still try to dilate with your other eye. Also your pupil/s will stretch like in the pictures.