Parents used to teach, if you read in the dark (on paper, not on a screen, I must add), you’re ruining your eyes. But if you think about it: wtf does low light do to your eyes? By that logic, you’re constantly ruining your eyes while sleeping.

The theory is that frequently straining your eyes is an issue, so reading in conditions that are difficult to see in will weaken them, not that dark itself hurts your eyes.