What is the difference between contact lens exam and annual eye exam?

There are 3. There are three distinct services typically offered. The first is the eye exam. This determines if the eyes are healthy. The second is the refraction. This determines a glasses prescription. The third is a contact lens fitting. This determines a contact lens prescription. Generally there is a fee for each service.
Eye exam. By contact lens exam, i would assume you mean a refractive check up. It will help determine whether you need contacts. However, a complete proper eye exam needs to be conducted by an ophthalmologist (an md) who can dilate your eyes and look at the actual lens and the back of the eye (retina). This should be an annual exam just like your annual physical.