CMV (cytomegalovirus) infection is a common herpes virus infection with a wide range of symptoms: from no symptoms to fever and fatigue to severe symptoms involving the eyes, brain, or other internal organs. Usually, this infection causes no symptoms. Serious infections typically develop only in infants infected before birth (causes blindness) and in people with a weakened immune system such people with AIDS or those who have received an organ transplant. Once get infected, the virus remains dormant (inactive) in various tissues for life. Weakening of immune system may cause reactivation of virus. Asymptomatic or mild CMV infection is usually not treated. It subsides on its own. Because your son has already lost his vision and now he is asymptomatic, so no treatment is needed as this stage. Treatment is required in patients with AIDS or organ transplant. So relax and take care of your son. If any complications occur then contact CMC hospital, Vellor, India I hope this information will help you Thanks!