A Doctor of Optometry (O.D.) degree is required to work as an optometrist. Most schools of optometry require three years (90 credits) of undergraduate work for admission, although some schools require a bachelor's degree. The Optometry Admissions Test (OAT) is required for optometry school and should be taken during the application process about a year in advance of when a student hopes to matriculate. Each of the optometry schools in the United States and Puerto Rico has slightly different requirements. The basic requirements for most schools are contained below in the Preoptometry Concentration. It is essential that applicants obtain catalogs from the specific schools or colleges of optometry where they plan to apply to see what changes are needed. For example, some schools may require an extra semester of anatomy and physiology, organic chemistry, or psychology. The Association of Schools and Colleges of Optometry has a Web site of information on all of the schools of optometry at www.opted.org.