Leukemia is often considered a cancer that doesn't spread because it is widespread through the blood at diagnosis. But there are sites outside of the bone marrow/blood that leukemia can settle in. These are called extramedullary sites, and include the central nervous system, testicles, and eyes. It is extremely rare to have leukemia settle in the eye, but it is absolutely possible.
What exactly do you want to know? Because it sounds like his eye is involved, it's likely to be acute lymphoblastic leukemia. Treatment is long- about 3.5 years for boys, though he may end up having altered treatment because of the eye. He'll be in the hospital for a while at first, and then when his counts are high enough, he'll be able to go home. Much of his treatment will be done outpatient, but some will be inpatient. He won't be able to attend school for quite some time.
Work in pediatric oncology. Had a patient relapse with leukemia in the eye recently.