CMV infection that causes symptoms normally occurs only in those with weakened immune systems. People with AIDS who have a CD4 count of less than 100 should be examined regularly for retinitis even if they don't have symptoms.
Drew WL. Cytomegalovirus. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 399.