Anisocoria is a pathological condition of enequal pupil size.  It can be caused byphysical damage, drugs or more seriously, cranial nerve palsy.  

Mydriasis is the widening of the pupil diameter.  It is usually accomodated with relaxation of ciliary muscle, which allows far vision and widening of palpebral fissure (widening of eyelids).  Mydriasis is caused by stimulation of the sympathetic nervous system.

Miosis is constriction of the pupil. This is caused by stimulation of the PS nervous system