Buying glasses or contacts requires the services of an ophthalmologist, optometrist, or optician. If you’re like most of us, you can’t remember which of these “three Os” does what, even if you’ve been told a dozen times. So here it is again:

Ophthalmologists are M.D.s who diagnose and treat disorders of the eye. They are college graduates who have completed four years of medical school followed by an internship and additional clinical training. They check eyes for vision problems, eye diseases and abnormalities, and symptoms of general body disorders, such as diabetes and hypertension. They treat eyes with drugs, surgery, and other means, and prescribe corrective eyeglasses and contact lenses. Almost all ophthalmologists expect you to take the prescription they write for eyeglasses to one of the other types of specialists, but some dispense contact lenses.

Optometrists are not medical doctors, they are properly referred to as doctors. They are college graduates who have completed four years of postgraduate training in optometry. Like ophthalmologists, optometrists perform eye exams that diagnose a wide range of eye problems as well as symptoms of general health problems. Some use visual training techniques to counter certain kinds of vision problems. They also prescribe, and usually dispense, both eyeglasses and contact lenses.

Opticians, unlike the other two types of specialists, are not required to have extensive training. In Virginia, they must complete two years of training beyond high school and pass a state examination. The District and Maryland have no training or examination requirements. Opticians are not allowed to prescribe, but they fit, supply, and adjust eyeglasses and sometimes contact lenses prescribed by an ophthalmologist or optometrist. Some opticians grind eyeglass lenses to the correct prescription, but most purchase lenses from a wholesaler and then fit them into the frame.

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