Base curve in contact lenses prescription
Base curve refers to the general shape of a contact lens. A contact lens fits over a person's cornea and needs to fit snugly and comfortably. Of course all people potentially have a slightly different sized cornea hence the need for a contact lens prescription which is the end result of a contact lens fitting performed by a certified optician. A person's cornea should of course not change size so if you have already been fitted and know your base curve and diameter and feel your vision has not changed in many years you may question the need to get a new examination and new contact lens prescription each and every year in order to purchase contact lenses on-line. For most people the regular checkups give them peace of mind that their prescription has not in fact changed. Additionally the optician will be checking the overall health of the patient's eyes including test for glaucoma and other degenerative eye conditions. You should not buy contact lenses without a doctor prescription unless it's recently expired and you are confident your eyes are healthy and your vision has not decreased. For some this may seem risky but consider that young adults that have yet to need eyeglasses or contact lenses are not required by law to have their eye sight checked by a doctor or a machine in order to retain a drivers license.
This page is in process and will contain links to mulliple reputable sources for more complete definitions of base curve as it relates to prescription contact lenses. Visit this wikipedia link for more information pertaining to contact lenses and base curve.