The prescription you receive at the end of your exam is typically a prescription for eyeglasses only. An accurate prescription for contact lenses can only be issued after several steps are taken that are not included in a routine eye exam. The contact lens fitting involves special measurements of the curvature of the front surface of your cornea and includes an evaluation of the tear film on the front of your eyes. If your eyes are dry, contact lenses may not be for you. Some contact lenses may work better than others. Your doctor will also carefully evaluate the health of the cornea with an instrument to make sure there are no other problems that could make contact lens wear difficult for you. Next, trial lenses will be applied to your eyes and evaluated by the doctor or lens technician to assess the fit of the lenses. This step is also done at each follow-up visit in the fitting process. Sometimes, lenses that appear to fit fine when first applied can tighten up after several hours of wear. Checking the fit of your lenses several times is essential to ensure your lenses continue to fit properly and cause no adverse effects to the cornea. Finally, an explanation of how long to wear your lenses and how to care for them is an important part of the contact lens fitting. After your doctor is sure your lenses fit properly, provide satisfactory vision and comfort, and are causing no harm to your eyes, your final contact lens prescription can be written. It includes contact lens power (often slightly different than spectacle lens power), contact lens base curve, and diameter.