Mydriasis disorders e.g. epilepsy, stroke, and impending brain herniation are known to lead to temporal mydriasis as well. A brain catastrophe, or a rapidly increasing brain mass, can cause compression of the oculomotor nerve. In cases of head injury or orbit trauma (eye injury), the iris sphincter (the muscle responsible for closing the pupil) or the nerves controlling it can be damaged, reducing or eliminating the normal pupillary light reflex. A mydriatic is an agent that induces dilation of the pupil. Drugs such as tropicamide are used in medicine to permit examination of the retina and other deep structures of the
Sum of normally distributed random variables variables is normal, with its mean being the sum of the two means, and its variance being the sum of the two variances (i.e., the square of the standard deviation is the sum of the squares of the standard deviations). If one is to get the conclusion that the sum is normally distributed, the assumption that "X" and "Y" are independent cannot be dropped, although it can be weakened to the assumption that "X" and "Y" are jointly, rather than separately, normally distributed. (See here for an example.) The result about the mean holds in all cases, while the result