Can circle lens contacts harm your eyes when you don't wear contacts?

You should always get your eyes fitted for contact lenses by your eye doctor, even if you don't need prescriptive lenses. This, combined with safe shopping, will help keep your eyes safe. Circle contact lenses, like any contact lens, is a medical device and needs to be fitted to your eye for a safe fit and worn under the advice of your eye doctor.
There are circle lenses available in non-prescriptive powers. This is a page that shows a before and after as well as an example of FDA approved circle lenses available. I like this site because they ask for prescriptions.