You may have the dilated eyes when you read, especially when you read something interesting that you have a favor on. However, if you have the eyes problems, you may also have the dilated symptom. Thus, you'd better go to have a check on your eyes to see whether there is the problem for your eyes.
You'd better not to read when you got dilated pupils, because the dilated pupils make your eyes difficult in focusing or reading. The vision up close is affected. If you insist reading with your dilated pupil, you might find it challenging. I suggest you to take a rest for at least 3-4 hours until your eyes get back to normal function. If you need to go outside into a bright environment, it would be better for you to wear sunglasses. Because your pupils are dilated, which work as camera aperture, the dilated pupils will let too much light into your eyes, and damage your eyes. You should note what medication you are taking can make your pupils dilated.
Well, of course, it can just affect your reading. Generally speaking, when you have dilated pupils, it will be difficult for your eyes to have reading. According to some experts, when dilated pupils occur, the black part of the eye will be bigger than normal one. And that can be harmful and annoying. Of course, for some people, it will just lead to blurred vision. And there are many reasons which can lead to dilated pupils. For example, when you have high blood pressure and are anxious, it is possible to lead to dilated pupils.