opportunistic condition A condition that occurs especially or exclusively in persons with weak immune systems due, for example, to AIDS, cancer, or immunosuppressive drugs, such as corticosteroids or chemotherapy. An opportunistic condition may be an infection, such as toxoplasmosis or cytomegalovirus (CMV), or a tumor, such as Kaposi sarcoma in AIDS. See also opportunistic infection;…
opium An addictive narcotic drug that is derived from the unripe seedpods of the opium poppy. Preparations of opium were called laudanum. Derivatives of opium include paregoric (a drug used to treat diarrhea), morphine, and heroin. For centuries, opium was used as a painkiller in the Middle East and Asia. It gained great popularity in…
opisthotonos A great rigid spasm of the body, with the back fully arched and the heels and head bent back. Opisthotonos occurs in meningitis, especially in infants, due to irritation of the membranes surrounding the brain and spinal cord. It also occurs with depressed brain function and injury to the brain. Opisthotonos is an ominous…
opioid 1 A synthetic narcotic that resembles the naturally occurring opiates. 2 Any substance that binds to or otherwise affects the opiate receptors on the surface of the cell. Opiate receptors are the cellsurface proteins to which opiates and opiods bind in order to cause their effects.
opiate A medication or an illegal drug that is derived from the opium poppy or that mimics the effect of an opiate (a synthetic opiate). Opiate drugs are narcotic sedatives that depress activity of the central nervous system, reduce pain, and induce sleep. Side effects may include oversedation, nausea, and constipation. Long-term use of opiates…
ophthalmoscopy Examination of the interior of the eye, including the lens, retina, and optic nerve, using an ophthalmoscope. Ophthalmoscopy can be indirect or direct. Indirect ophthalmoscopy, which is generally performed by an ophthalmologist, employs a headlamp device to shine a very bright light into the eye. Direct ophthalmoscopy is in more common usage by many…
ophthalmoscope A lighted instrument that is used to examine the inside of the eye, including the retina and the optic nerve.
ophthalmoplegic migraine See migraine, ophthalmoplegic.
ophthalmopathy Any eye disease.
ophthalmology The art and science of eye medicine.
ophthalmologist A physician who practices ophthalmology.
ophthalmitis See ophthalmia.