Pupil
The opening of the iris. The pupil may appear to open (dilate) and close (constrict), but it is really the iris that is the prime mover; the pupil is merely the absence of iris. The pupil determines how much light is let into the eye. Both pupils are usually of equal size. If they are not, the condition is called anisocoria.
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- Pupil dilation test
An procedure that enables an eye care professional to see more of the retina, the light-sensitive layer of tissue at the back of the eye. Dilating (widening) the pupil permits the retina to be examined for signs of disease. To do this, drops are placed into the eye to dilate the pupil. After the examination, […]
- Purine
One of the two classes of bases in DNA and RNA. The purine bases are guanine (G) and adenine (A). Uric acid, the offending substance in gout, is a purine end-product.
- Purpura
Hemorrhage (bleeding) into the surface of the skin. The area of skin with purpura is greater than 3 millimeters in diameter. The appearance of an individual area of purpura varies with the duration of the lesions. Early purpura is red and becomes darker, then purple, and brown-yellow as it fades.
- Purpura, acute thrombocytopenic
Sudden onset of low blood platelet levels, with bleeding into the skin and elsewhere. Abbreviated ATP. ATP can have many causes; for example, it can be a potentially serious complication during the acute phase of measles infection.
- Purpura, thrombotic thrombocytopenic (TTP)
A life-threatening disease involving embolism and thrombosis (plugging) of the small blood vessels in the brain. It is usually caused by inhibition of an enzyme in the blood called ADAMTS13 which breaks down another protein in the blood called Von Willebrand Factor into smaller pieces. TTP is characterized by platelet microthrombi (tiny traveling clots composed […]