If a person has eight-ball hyphema, can he see?

No. A 8-ball hyphema is an emergency go the er now.
Very little. This is a clotted amount of blood centrally in the front of the eye usually wrapping around the iris. Vision is limited by the dense red clot in the way and generally such an eye can only see light and dark. Depending upon the cause, the vision can clear completly but there can also be some damage. You might need surgery to clear it out and need close attention by your ophthalmologist.