O

OCULAR:
Pertaining to the eye.

OFFICE OF AIDS RESEARCH (OAR):
An office within the National Institutes of Health (NIH) that coordinates AIDS research in all of the participating NIH institutes. Internet address: http://www.nih.gov/od/oar/index.htm.

OFF-LABEL USE:
A drug prescribed for conditions other than those approved by the FDA.

ONCOLOGY:
Study of cancers or other tumors.

OPEN-LABEL TRIAL:
A clinical trial in which doctors and participants know which drug or vaccine is being administered.

OPPORTUNISTIC INFECTIONS:
Illnesses caused by various organisms, some of which usually do not cause disease in persons with normal immune systems. Persons living with advanced HIV infection suffer opportunistic infections of the lungs, brain, eyes, and other organs. Opportunistic infections common in persons diagnosed with AIDS include Pneumocystis carinii pneumonia; Kaposi's Sarcoma; cryptosporidiosis; histoplasmosis; other parasitic, viral, and fungal infections; and some types of cancers.

ORAL HAIRY LEUKOPLAKIA (OHL):
A whitish lesion that appears on the side of the tongue and inside cheeks. The lesion appears raised, with a ribbed or "hairy" surface. OHL occurs mainly in persons with declining immunity and may be caused by Epstein-Barr virus infection. OHL was not observed before the HIV epidemic.

ORGANELLE:
Any one of various particles of living substance bound within most cells, such as the mitochondria, the Golgi complex, the endoplastic reticulum, the lysosomes, and the centrioles.

OROPHARYNGEAL:
Relating to that division of the pharynx between the soft palate and the epiglottis. Pharynx is a tube that connects the mouth and nasal passages with the esophagus, the connection to the stomach. Epiglottis is a thin, valvelike structure that covers the glottis, the opening of the upper part of the larynx (the part of the throat containing the vocal cords), during swallowing.

ORPHAN DRUGS:
An FDA category that refers to medications used to treat diseases and conditions that occur rarely. Therefore, there is little financial incentive for the pharmaceutical industry to develop such medications. Orphan drug status gives a manufacturer specific financial incentives to develop and provide such medications.