Answer:c. the back of his skull
Step-by-step explanation:
The nerves that connect to your eye balls runs through your skull so even if it is not the eye that is not by the ball but anything that affect the skull will have an impact on these nerves and retinal detachment which in return will have an impact on your vision.
Most of the muscles that controls your eyes and its vision are all connected into your skull so this connection will affect your eyes of the skull is hurt.
The ball hitting the back of his skull might have disturbed these nerves and lead to disruption of his vision.