Coma

1. In medicine, a coma is a profound state of unconsciousness, which may result from a variety of conditions including intoxication (drug, alcohol or toxins), metabolic abnormalities (hypoglycemia, hyperglycemia, ketosis, etc.), central nervous system diseases, stroke, head trauma, seizures, and hypoxia. The metabolic abnormalities are the most common causes of coma. The difference between coma and stupor is that a patient with coma cannot give a suitable response to either noxious or verbal stimuli, whereas a patient in a stupor can give a rough response (like screaming) to a noxious stimulus.

Coma is also to be distinguished from the permanent vegetative state which may follow it. This is a condition in which the individual has lost cognitive neurological function and awareness of the environment but does have noncognitive function and a preserved sleep-wake cycle. Spontaneous movements may occur and the eyes may open in response to external stimuli, but the patient does not speak or obey commands. Patients in a vegetative state may appear somewhat normal. They may occasionally grimace, cry, or laugh.

Likewise, coma is not the same as brain death, which is the irreversible cessation of 'all' brain activity. One can be in a coma but still exhibit spontaneous respiration; one who is brain-dead by definition cannot do so.

The outcome for coma and vegetative state depends on the cause and on the location, severity, and extent of neurological damage: outcomes range from recovery to death. People may emerge from a coma with a combination of physical, intellectual, and psychological difficulties that need special attention. Recovery usually occurs gradually, with patients acquiring more and more ability to respond. Some patients never progress beyond very basic responses, but many recover full awareness.

A coma proper rarely lasts more than 2 to 4 weeks. Some patients who have gone into vegetative state may go on to regain a degree of awareness. Others may remain in a vegetative state for years or even decades. The most common cause of death for a person in a vegetative state is infection such as pneumonia.

There have been controversies and legal cases over whether to keep comatose patients alive for long periods using life support equipment.

A temporary coma is sometimes deliberately induced (using drugs) to reduce swelling of the brain after injury.

Some of the information in this section is from the public domain resource provided by the National Institute of Neurological Diseases and Stroke at http://www.ninds.nih.gov/health_and_medical/disorders/coma_doc.htm

2. In astronomy, a coma is the tail of a comet produced by vapor boiled off the comet as it nears the sun.

3. In optics, a coma is an optical aberration in an astronomical telescope which causes a V-shaped flare to the image of a star. About coma in an Newtonian telescope