It is highly important to always receive a comprehensive eye exam once a year, for those between the ages of 18-39, as recommended by the American Optometric Association. Comprehensive eye exams, in addition to determining your glasses and contact lens prescription, allow a doctor to check for a number of potential eye diseases that may affect your vision and overall eye health: glaucoma, macular degeneration, cataracts, and many others.
A great follow up information site is at the American Optometric Association at: LINK