Optometry and Vision Science is a health care profession concerned with the health of the eyes and related structures, as well as vision, visual systems, and vision information processing in humans. Optometrists (also known as ophthalmic opticians outside the United States and Canada) are trained to prescribe and fit lenses to improve vision, and to diagnose and treat various eye diseases. In the United States and Canada optometrists are considered Doctors of Optometry and are held to the same legal standards as any physician. In all U.S. states optometrists are licensed to diagnose and treat diseases of the eye through topical diagnostic and therapeutic drugs, and oral drugs in 47/50 states. Doctors of Optometry are also able to perform certain types of laser surgery in some states. In other countries patients are referred to other healthcare professionals, such as ophthalmologists, neurologists and general medical practitioners for further treatment or investigation.