Dictionary

pinealoblastoma See pineoblastoma.

pinealocytoma See pinealoma.

photodynamic therapy A form of treatment that uses a photosensitizing agent, administered by mouth or intravenously, which concentrates selectively in certain cells, followed by exposure of the involved tissue to a special light (such as laser or ultraviolet light), in order to destroy as much of the abnormal tissue as possible. For example, photodynamic therapy…

photophobia Sunglasses may also help.

photorefractive keratectomy A kind of laser eye surgery that is designed to correct vision by changing the shape of the cornea, potentially eliminating or reducing the need for glasses or contact lenses. Abbreviated PRK. A laser is used to remove the outer layer of the cornea and flatten the cornea. PRK is done in a…

photosensitivity Oversensitivity of skin to light. Photosensitivity can be a side effect of medications or result from diseases, such as lupus. Treatment depends on the severity of the reaction and the cause. Photosensitivity can be prevented by avoiding skin exposure to ultraviolet light.

phototherapy Treatment with light. For example, a newborn with jaundice may be put under special lights to help reduce the amount of bilirubin pigment in the skin.

phototoxicity An exaggerated response to ultraviolet radiation (sunlight) characterized by rapidly developing or severe sunburn. Phototoxicity may be associated with certain medications, including the antibiotic tetracycline.

phrenology The study of variations in the size, shape, and proportion of the cranium. Phrenology was a pseudoscience of the 18th and 19th centuries, based on the belief that a person’s character could be learned by looking with care at the shape of the person’s head and noting each and every bump and depression in…

PHS Public Health Service. See United States Public Health Service.

physiatrist A physician who specializes in physical medicine and rehabilitation. Physiatrists specialize in restoring optimal function to people with injuries to the muscles, bones, tissues, or nervous system, such as stroke victims.

physical map A map of the locations of identifiable landmarks on chromosomes. Physical distance between landmarks is measured in base pairs. The physical map differs from the genetic map, which is based purely on genetic linkage data. In the human genome, the lowest-resolution physical map is the banding patterns of the 24 different chromosomes. The…