Please answer! what would cause your pupils to not dilate?

Pupils dilate and: constrict under control of cranial nerve 2 and 3. 2nd senses light and 3d adjusts pupil to control light input. No dilation = deficit in one or the other or a medication in the eye has poisoned muscle function. Would be very unlikely to inadvertently notice that both pupils do not dilate. Close eyes in bright room then open while friend observes. If they constrict they must have been dilated.