Cytomegalovirus (CMV) retinitis is an infection of the retina caused by the common cytomegalovirus. While harmless in people with healthy immune systems, the virus can become active and cause serious disease in those with severely compromised immune systems. This includes people with advanced HIV/AIDS, organ transplant recipients on immunosuppressive drugs, or patients undergoing certain chemotherapy. The virus attacks retinal cells, leading to inflammation and damage that can cause irreversible vision loss or blindness if left untreated. Modern therapies aim to halt viral replication, control the infection, and preserve as much vision as possible.
Primary Antiviral Medications
The treatment for CMV retinitis centers on antiviral medications designed to stop the cytomegalovirus from multiplying. The choice of drug depends on the retinitis severity, the patient’s health, and their ability to tolerate side effects. These medications suppress the virus to an inactive state to prevent further retinal damage but do not cure the infection.
A primary medication is ganciclovir, which works by interfering with the virus’s ability to replicate its DNA. A related and more commonly used drug is valganciclovir, a prodrug that is converted into ganciclovir after being taken orally. Its major advantage is high bioavailability as a pill, making it a convenient option for long-term therapy and avoiding intravenous lines.
When ganciclovir or valganciclovir cannot be used due to resistance or intolerance, other medications are available. Foscarnet is a common intravenous alternative with a different mechanism of action, making it effective against resistant virus strains. However, it can be associated with kidney-related side effects.
Another potent antiviral is cidofovir, also given intravenously, which has a long-lasting effect allowing for less frequent dosing. Cidofovir is reserved for specific situations due to its potential for significant kidney toxicity, which requires careful management. In some cases of drug resistance, a combination of medications may be used to control the infection.
Treatment Delivery Methods
Antiviral medications for CMV retinitis can be administered through different methods. The choice depends on the location and severity of retinal lesions and the need to control the virus systemically. These methods are categorized as either systemic (whole-body) or local (eye-specific).
Systemic therapy is necessary because CMV is a body-wide infection in immunocompromised individuals. Oral valganciclovir is the most common systemic treatment, while intravenous (IV) infusions are another option. IV treatments ensure high drug concentrations circulate throughout the body, controlling the virus in other organs.
Local therapy delivers medication directly to the site of infection in the eye. The most common form is an intravitreal injection, where a small needle injects an antiviral drug into the vitreous humor. This method achieves a high concentration of medication at the retina, which is useful for sight-threatening lesions near the optic nerve or macula. These injections may be used alongside systemic therapy to gain rapid control of the infection.
A less common local delivery option was a surgical implant. The ganciclovir intraocular implant was a small device surgically placed inside the eye that slowly released medication over several months. This device is no longer available in the United States, having been replaced by effective oral medications and intravitreal injections.
The Two Phases of Therapy
Treating CMV retinitis involves a structured, two-stage approach to first control the active infection and then prevent its return. This process is divided into an initial induction phase and a long-term maintenance phase, highlighting that treatment is a sustained commitment.
The first stage is the induction phase, an aggressive, high-dose treatment period lasting two to three weeks. During this time, patients receive high doses of antiviral medication, such as oral valganciclovir twice daily, to quickly stop viral replication. The goal is to halt the progression of retinal damage and stabilize vision.
Once ophthalmologic exams confirm the retinitis is inactive, the patient transitions to the maintenance phase. This second stage involves a lower, daily dose of antiviral medication to prevent recurrence, such as reducing the oral valganciclovir dose to once daily. The maintenance phase continues long-term until the individual’s immune system recovers enough to control the virus.
For patients with HIV, this recovery is often marked by a sustained CD4+ T-cell count above 100 cells/µL for at least three to six months.
Monitoring During and After Treatment
Continuous monitoring is a standard part of managing CMV retinitis during and after treatment. This follow-up care ensures the medication is working, checks for side effects, and screens for long-term complications.
Regular, dilated eye examinations are performed to manage treatment. An ophthalmologist will perform these exams frequently in the initial stages to track the retinal lesions and confirm they are healing. Fundus photographs are often taken to document the retina’s appearance and help detect any subtle changes or early signs of relapse.
Systemic antiviral therapies require regular blood tests to monitor for potential side effects. Doctors will watch for issues like myelosuppression, which is a decrease in blood cell production, and also monitor kidney function. These tests allow for dosage adjustments or medication changes if significant side effects develop.
Even after successful treatment, the healed retina can be fragile. One concern is retinal detachment, where the retina pulls away from the back of the eye due to scarring from the healed retinitis. Another potential complication is immune recovery uveitis (IRU), where a strengthening immune system causes inflammation in the eye, leading to problems like cataracts or macular edema.