An eye exam for contact lenses is a comprehensive examination. The eye doctor will check the health of your eye and also do a refraction, a check of your vision and how well you see. The refraction determines your prescription. If you wear contact lenses, the prescription is written as "Power" or "Strength" and can be low (minimal) or high (very strong).
Your prescription for contact lenses is different from your glasses prescription. During your eye exam, the doctor will take special measurements with a keratometer, an ophthalmic instrument that measures the curves of your eye. According to the Ohio State University Medical Center, your contact lens prescription usually includes your contact lens power or strength (also called dioptres) and your lens base curve and diameter.
Contact lenses are available as stock lenses or custom made. Stock lenses are pre-made in certain sizes and strengths. Custom-made lenses can be prescribed for almost every prescription. Laboratories make custom contacts in powers up to 30 dioptres, according to All About Vision.
According to the American Optometric Association, most contact lens wearers are nearsighted. Stock brands average from 8 dioptres (written as +8.00 for farsighted prescriptions) to 12 dioptres (written as -12.00 for nearsighted prescriptions). Different contact lens companies make lenses in various strengths. Your doctor can determine which lens is best for your eyes and whether custom lenses can be prescribed in a higher strength.
In the near future, contact lenses may be made with higher strengths and other capabilities. In the September 2009 issue of "IEEE Spectrum," Babak A. Parviz, a bionanotechnology expert at the University of Washington, states that he and his students are making contact lenses with built-in circuits and LEDs in the university lab. Pariz estimates that contact lens technology potential and capability will increase greatly within the next 5 to 10 years.
By law, you are entitled to a copy of your current contact lens and spectacle prescription. The Federal Trade Commission issued the Contact Lens Rule that gives patients the right to have their prescriptions for contacts after completion of eye exams, no matter how strong the prescription and order lenses from anyone who is licensed to sell contact lenses.