Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eyeball and orbit. An ophthalmologist is a specialist in medical and surgical eye disease. Their credentials include an M.D. or D.O. degree in medicine, followed by an additional four years of residency. Additional training may be sought through a fellowship in a particular specialty of eye pathology. Ophthalmologists are allowed to medically treat eye disease, implement laser therapy, and perform incisional surgery when warranted.