depending on how you have your sprites set up, this is fairly simple.
Sprite - set angle toward position - mouse.x,mouse.y
Sprite - set angle - angle(eye.x,eye.y,mouse.x,mouse.y)
if you are using two sprites (one for the eye and one for the iris) it gets a bit more difficult.
You could just set the origin point for the iris at the middle of the eye-sprite and use above events, but if you want more realistic eye-movement, being able to go to the center of the eye-sprite, more calculating is needed.