Dilated pupils. There are many chemicals that can cause mydriasis of the pupils, these are all self limited. Dilating eye drops used in the office cause mydriasis also self limited. Trauma, a forceful blow to the eye, may damage the pupillary muscles and can result in a irreversible mydriasis.
Drug effect. Ecstasy contains a naturally derived drug which has adrenergic effects. One of these is to dilate eyes. This effect is small from systemic use of ecstasy but if you get some powder in your eye, you may experience a short term eye dilation (mydriasis).