Following primary infection, cytomegalovirus (CMV) establishes latent infection in myeloid progenitor cells and intermittent viral reactivation from activated macrophages or dendritic cells, which is brought under control by strong virus-specific CD4+ T-cell and CD8+ T-cell responses. CMV retinitis characterized by spreading retinal necrosis due to viral cytopathic effect occurs in patients who have impaired T-cell function as a result of transplantation, AIDS, or immuno-suppressive treatment. The diagnosis of CMV retinitis can be confirmed by PCR amplification of viral DNA in aqueous. When administered intravenously, the antiviral drugs Ganciclovir and Foscarnet have modest penetration into the vitreous compared with direct intra-vitreal injection. In randomized trials of HIV-associated CMV retinitis, a Ganciclovir implant was consistently superior to intravenous Ganciclovir in preventing progression of retinitis. CMV is also implicated in two forms of anterior segment disease in immuno-competent adults, namely CMV anterior uveitis and CMV corneal endotheliitis.