There are many causes of pupil dilation, commonly including diminished ambient light in healthy people, use of dilating agents to dilate the pupil, pathological conditions such as intracranial hematomas and tumors, acute glaucoma, epilepsy and retrobulbar optic neuritis, drugs, etc. Coma with dilated pupils often represents an acute and critical condition, and once it occurs, the cause should be identified and treated as soon as possible.