A routine eye examination is a good idea even if you see fine. An eyeglass prescription may be needed to avoid eye strain, tiredness or headaches. You may have small changes to your vision that may not be apparent, but over the course of several years these small changes lead to significant changes in your prescription that may make your new glasses very difficult to adapt to. Many medical problems that are often undiagnosed may be apparent in the course of an eye exam. These conditions may be sight threatening or even life threatening.