The statement that a dilated pupil must kill is incorrect. The intensity of light causes a change in the size of the pupil. If the light is weak, the pupil will become larger. In addition to regulating the effect of light, diseases can also cause pupil dilation, such as intracranial hematoma, cranial trauma, encephalitis, tail gas poisoning, and glaucoma. There are also medications used, such as atropine, neurontin, and epinephrine that can also cause the pupil to dilate. In some patients with secondary glaucoma, poor atrial circulation can also cause the pupil to dilate. Many clinicians regard the pupil as a sensitive indicator of vital function. If the pupil is unresponsive to light or disappears, and if the pupil becomes dilated, it means that death is imminent, and in comatose patients the pupil will gradually increase in size as the loss of consciousness increases, which is a sign of the end of life. When the pupil is dilated, it does not shrink even when exposed to bright light, so photophobia can occur, causing damage to the fundus if the light shines directly back into the eye. When a patient has an unexplained dilated pupil, it is recommended that he or she seek prompt medical attention from an emergency department or ophthalmologist to prevent delays.