CMV retinitis is a viral infection of the retina, the light-sensitive tissue at the back of the eye. It is caused by the cytomegalovirus (CMV), a common virus that remains dormant in healthy individuals. The condition arises when the virus reactivates in people with compromised immune systems, leading to inflammation and retinal damage that can cause vision loss.
Risk Factors and Causes
Cytomegalovirus (CMV) is a widespread virus in the herpes family that establishes a lifelong, dormant infection controlled by a healthy immune system. CMV retinitis occurs when immune defenses are severely weakened. This allows the latent virus to reactivate, multiply, and spread to the retina.
The primary risk factor for CMV retinitis is severe immunocompromise. This condition is most frequently seen in individuals with advanced HIV/AIDS, particularly when their CD4+ T-cell counts fall to low levels. Other at-risk populations include recipients of organ or bone marrow transplants who take immunosuppressant drugs to prevent rejection. Patients undergoing intensive chemotherapy for cancer may also have a weakened immune system, making them susceptible.
Identifying Symptoms
The onset of CMV retinitis can be subtle, and individuals may not notice symptoms immediately. The first signs often include floaters, which look like dark spots or cobwebs drifting across the field of vision. This may be accompanied by a gradual blurring of vision over several days, reflecting inflammation and damage within the retina.
As the infection progresses, patients might experience blind spots (scotomas), which can appear to shimmer or move. Another symptom is the loss of peripheral vision, creating a sensation of tunnel vision. Although the condition is often painless, some individuals experience eye pain or increased sensitivity to light (photophobia). Symptoms usually start in one eye but frequently advance to the other.
The Diagnostic Process
Confirming a diagnosis of CMV retinitis requires a thorough eye examination by an ophthalmologist. The doctor dilates the patient’s pupils with eye drops to get a clear, unobstructed view of the retina and other structures at the back of the eye. This examination is performed with an instrument called an ophthalmoscope.
During the examination, the ophthalmologist looks for signs of viral activity and retinal damage. The infection creates a characteristic appearance on the retina, described as a “pizza pie” or “brushfire” pattern. This pattern consists of retinal necrosis (tissue death) combined with intraretinal hemorrhage (bleeding), and the doctor will assess the extent of the damage.
The ophthalmologist may take photographs of the retina to document the condition and track its progression. Blood or urine tests can detect CMV in the body but are not reliable for diagnosing retinitis, as the infection can be localized to the eye. The definitive diagnosis is based on the findings from the dilated eye exam.
Medical Treatments
The primary goal of treating CMV retinitis is to stop the replication of the cytomegalovirus, which halts further retinal damage. Treatment cannot restore lost vision but can prevent the infection from worsening. Management involves antiviral medications administered based on the infection’s severity and the patient’s overall health.
Systemic therapy involves medications that circulate throughout the body, delivered either orally or intravenously. Oral valganciclovir is a common medication for this purpose. Intravenous (IV) options include ganciclovir, foscarnet, and cidofovir, which are used for more severe infections. These treatments suppress the virus throughout the body.
Local therapy may also be used, which involves injecting antiviral medication directly into the eye’s vitreous cavity. These intravitreal injections of ganciclovir or foscarnet deliver a high concentration of medication to the infection site. Treatment is structured in two phases: an initial, high-dose induction period to control the infection, followed by a long-term, lower-dose maintenance phase to prevent recurrence. Addressing the underlying cause of the weakened immune system is also part of the management plan.
Disease Progression and Potential Complications
Without medical intervention, CMV retinitis progressively destroys retinal tissue, leading to irreversible vision loss and potential blindness within months. While treatment can halt the disease’s progression, any vision lost from retinal damage is permanent. Early detection and prompt therapy are important for preserving sight.
Even with successful treatment, the infection can recur if the immune system remains compromised, which requires regular monitoring. A major complication of CMV retinitis is retinal detachment. The inflammation and necrosis from the virus can weaken the retinal tissue, making it fragile and prone to tears.
A retinal tear allows fluid to seep underneath, lifting the retina from the tissue that provides its oxygen and nutrients. This is a medical emergency requiring urgent surgery to reattach the retina. If untreated, a retinal detachment leads to permanent blindness in the eye. Laser surgery may be performed to reduce the risk of detachment in a fragile retina.