From the www.abop.org website:
Since 1916, nearly 27,000 ophthalmologists have challenged themselves to meet the rigorous certification standards established by The American Board of Ophthalmology. The first medical specialty board founded in the United States, The American Board of Ophthalmology awards the only medical specialty certificate in ophthalmology recognized by both the American Board of Medical Specialties (ABMS) and the American Medical Association (AMA).
Board Certification is a voluntary process designed to assure quality eye care for the American people by assessing the knowledge, skills and experience requisite to the delivery of quality patient care. It is an additional step beyond state licensure and an ophthalmologist's extensive medical education experience.
Certification is granted to ophthalmologists who meet a series of accredited medical training requirements in ophthalmology, sign a practice pledge indicating their intent to practice with compassion, integrity and respect for human dignity, and complete an intensive evaluation process which includes two examinations: a written qualifying examination and an oral examination.