How do i know that i need new glasses?

Blurred vision: If the distance vision has become blurred with your current glasses so that it is difficult to see road signs, drive at night, read tv print, etc. Then a new prescription may be needed. If for reading, new glasses may be needed if you feel eyestrain symptoms, if you have to hold material further away to read, or if the near vision is blurred or fluctuates in clarity.