Coma

1. In medicine, a coma is a state of decreased alertness, awareness or consciousness, 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. A persistent coma is called a vegetative state.

Patients can remain in a coma for months or years before recovering, though recovery after such a lengthy coma is unusual.

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

Coma is sometimes deliberately induced (using drugs) to prevent swelling after a brain injury.

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