Most eye exams consist of a vision component, or refraction, in addition to an ocular health evaluation. During the refraction the doctor will measure how well you are able to see, and then determine if any optical correction would assist you to see better.
The ocular health component consists of examination in and around the eyes to identify any current or emerging pathology. For a thorough evaluation of ocular health, dilation is needed to be able to fully examine the interior of the eye. Dilation is recommended annually for anyone who has a history of ocular pathology which is being monitored, or who is at high risk for development of any ocular health issue. For patients who see well and have no history or ocular symptoms, it is wise preventative medicine to still have an eye exam with dilation about every 2-3 years to monitor for anything inside the eye which might progress to cause problems if left unidentified and untreated.