Cytomegalovirus (CMV) retinitis is a serious viral infection of the retina, the light-sensitive tissue lining the back of the eye. The condition is caused by the Cytomegalovirus, a member of the herpesvirus family, and is classified as an opportunistic infection. CMV retinitis poses a significant threat to vision, leading to permanent damage and potential blindness, almost exclusively in individuals with severely compromised immune systems.
Understanding the Infection
The Cytomegalovirus is extremely common, infecting over half of the adult population globally, yet it typically remains dormant in healthy individuals. The immune system keeps the virus in check, preventing active disease. CMV retinitis occurs when immune defenses are severely weakened, allowing the latent virus to reactivate and travel to the eye. Once reactivated, the virus attacks and replicates within the retinal cells. This uncontrolled replication leads to full-thickness necrosis, or the death of the retinal tissue. The resulting inflammation, hemorrhage, and tissue death destroy the retina’s ability to convert light into neural signals, causing sight loss.
Populations Most At Risk
CMV retinitis develops when cell-mediated immunity, specifically T-cell function, is profoundly suppressed. Historically, the population at highest risk has been individuals with advanced Human Immunodeficiency Virus (HIV) infection or Acquired Immunodeficiency Syndrome (AIDS). The infection typically emerges when the CD4+ T-cell count drops below 50 cells per microliter of blood. While the risk has decreased significantly due to highly active antiretroviral therapy (HAART) for HIV, the condition remains a concern for those with poor treatment adherence. Other susceptible groups include organ transplant recipients who take immunosuppressive medications to prevent rejection. Patients undergoing intensive chemotherapy for cancer or those with hematological malignancies are also at heightened risk due to temporary immune suppression.
Symptoms and Visual Impact
The initial presentation of CMV retinitis is often insidious, meaning symptoms may be mild or absent, particularly in its early stages. The most common early signs include floaters, which are small specks moving in the field of vision, and a progressive blurring of sight. Patients may also experience photopsias, or flashing lights, caused by the inflammatory process irritating the retina.
As the infection progresses, it results in scotomas, which are fixed blind spots corresponding to the areas of dead retinal tissue. Ophthalmologists observe characteristic white, necrotizing lesions with associated retinal hemorrhage, sometimes described as having a “pizza pie” or “cottage cheese and ketchup” appearance. If the infection reaches the macula or optic nerve, central vision loss can occur rapidly. Untreated, the extensive scarring and tissue destruction can cause a rhegmatogenous retinal detachment, leading to irreversible blindness.
Diagnosis and Treatment Protocols
Diagnosis of CMV retinitis is primarily achieved through a comprehensive, dilated fundoscopic examination by an ophthalmologist. The physician looks for characteristic areas of retinal whitening, necrosis, and hemorrhage. While clinical appearance is often sufficient, confirmation may involve polymerase chain reaction (PCR) testing of fluid samples taken from the eye to detect the virus’s genetic material.
Treatment requires prompt antiviral therapy to halt viral replication and prevent further retinal damage. Frontline medications include valganciclovir, ganciclovir, foscarnet, and cidofovir. These drugs can be delivered systemically through oral tablets or intravenous infusion, or locally via intravitreal injections directly into the eye. Local injections provide a high concentration of the drug at the site of infection and may be used in combination with systemic therapy. Managing the underlying immune condition is paramount, such as optimizing HAART in HIV-positive patients, although a complication known as immune recovery uveitis (IRU) can sometimes occur as the immune response strengthens.