Many people don’t know this (I didn’t before I learned it), but a lot can be determined about your health through your eyes. That’s why it’s so important to get a proper eye exam every year.

Eye doctors can spot chronic illness and diseases through your eyes—all you have to do is schedule the exam and show up. This goes for everyone, whether or not you wear glasses or contact lenses.

Here are a couple reasons why annual eye exams are necessary for all of us, and what to expect when you go in for one.