Well, generally speaking, pupil dilation can be kind of annoying and serious. First, you should know that when dilated pupils occur, the black part of the eye is bigger than normal. And we can say that dilated pupils look like a big black circle. Of course, because of that your eyes may be painful. According to some experts, if the cause is high blood pressure, it will just make your eyes feel stressed. For the causes, some factors, such as high blood pressure, drug use, illness, trauma and anxiety can cause pupils to be dilated. So just be careful about it.