Do you have a headache? It's the most telling sign of a wrong prescription. Have you ever worn someone else’s glasses and suddenly felt dizzy with your head throbbing? You likely don’t have the same prescription as your friend.
Stare straight ahead with the other eye. Is your vision hazy or blurred? Repeat with the other eye. The blurred vision in one eye, while the other is closed is a sure sign that your glasses or lenses is incorrect.