Dictionary

oral Having to do with the mouth. For example, an oral solution is a solution that is given by mouth.

OR Operating room.

OPV Oral polio vaccine. See polio vaccine, oral.

optometrist A practitioner who provides primary eye and vision care, performs eye examinations to detect vision problems, and prescribes corrective lenses to correct those problems. Some optometrists also make and fit eyeglasses, but many leave that job to opticians. An optometrist is a doctor of optometry (OD), not an MD. When an optometrist detects eye…

optician A specialist in fitting eyeglasses and making lenses to correct vision problems. An optometrist performs eye examinations and writes prescriptions for corrective lenses; an optician fills that prescription.

optic neuroma A rare benign tumor of the optic nerve.

optic nerve pathways The course of the chemical and electrical impulse from light stimulating the retina as it passes from the optic nerve to the vision center of the brain. The left and right branches of the optic nerves join behind the eyes, just in front of the pituitary gland, to form a cross-shaped structure…

optic nerve The second cranial nerve, which connects the eye to the brain. The optic nerve carries the impulses that are formed by the retina—the nerve layer that lines the back of the eye, senses light, and creates impulses. These impulses are dispatched through the optic nerve to the brain, which interprets them as images….

optic Having to do with vision.

oppositional defiant disorder A behavior disorder of children and teens characterized by an ongoing pattern (for at least 6 months) of uncooperative, defiant, and hostile behavior toward authority figures that seriously disrupts normal day-to-day functioning. Symptoms include anger, defiance, temper tantrums, revenge-seeking behaviors, and hateful or mean talking. Abbreviated ODD. The cause of ODD is…

opportunistic microorganism A bacterium, virus, or fungus that takes advantage of certain opportunities to cause disease (opportunistic conditions). Opportunistic microorganisms are often ones that can lie dormant in body tissues for many years, such as the human herpesviruses, or that are extremely common but usually cause no symptoms of illness. When the immune system cannot…

opportunistic infection An infection that is not typically seen in healthy people, but occurs because a person’s immune system is weakened. Opportunistic infections are a particular danger for people with immunodeficiency, such as AIDS, or for those receiving immunosuppressive drugs such as chemotherapy for cancer. The HIV virus itself does not cause death, but the…