CMV retinitis is a sight-threatening eye infection caused by cytomegalovirus, a common herpesvirus that poses little danger to people with healthy immune systems but can devastate the retina when immunity collapses. Before effective HIV treatment existed, it was the leading cause of blindness in people with AIDS, and it remains a serious concern for anyone whose immune defenses are severely weakened. The disease is treatable with antiviral drugs, but outcomes depend heavily on how early it is caught and whether the underlying immune suppression can be reversed.
What Causes the Infection
Cytomegalovirus (CMV) belongs to the herpesvirus family. Most people contract it at some point in their lives, often in childhood, and it then lies dormant indefinitely. A healthy immune system keeps it in check with no symptoms. CMV retinitis occurs when the immune system weakens severely enough that the dormant virus reactivates and infects the retina, the light-sensing tissue at the back of the eye.
The retinal damage is partly caused by the virus itself destroying retinal cells, but immune-driven inflammation also plays a significant role. Research in a mouse model of newborn CMV infection found that the infection recapitulated features of human eye disease, including focal chorioretinitis, inflamed blood vessels, and disrupted barriers that normally protect the retina. Strikingly, blocking immune responses in these mice did not worsen the disease but instead prevented retinal pathology despite ongoing viral infection in the retina, suggesting the immune response itself drives much of the tissue damage.1Science Advances. Immune responses drive chorioretinitis and retinal pathology after neonatal CMV infection
Who Is Most at Risk
The degree of immune suppression is the single most important risk factor. CMV retinitis overwhelmingly strikes people whose CD4+ T-cell counts have dropped to very low levels. A systematic review found that roughly three-quarters of cases occur when CD4+ counts fall below 50 cells per microliter, a level of profound immune collapse typically seen in advanced, untreated HIV/AIDS.2The International Journal of Medical Science and Health Research. A Comprehensive Systematic Review of The Impact of HIV/AIDS on Ocular Manifestations: A Focus on HIV Retinopathy and Opportunistic Infections such as Cytomegalovirus (CMV) Retinitis For that reason, routine screening for CMV retinitis has traditionally been recommended only for patients with severe CD4+ depletion.3JAMA Ophthalmology. Cytomegalovirus Retinitis in HIV-Infected Patients With Elevated CD4+ Counts
People with HIV/AIDS are the most commonly affected group, but they are not the only ones at risk. Organ transplant recipients on immunosuppressive medications can also develop CMV retinitis, though the incidence is much lower, affecting roughly one to two percent of kidney transplant recipients.4PubMed Central. Presumed cytomegalovirus retinitis late after kidney transplant Certain newer immunosuppressive drugs used in transplant medicine may raise this risk further. Case reports suggest that kidney transplant patients treated with belatacept, a drug that blocks T-cell activation, may face an increased risk of CMV disease, including retinitis.5PubMed Central. Belatacept associated – cytomegalovirus retinitis in a kidney transplant recipient: a case report and review of the literature People undergoing chemotherapy, bone marrow transplant recipients, and those with congenital immune deficiencies are also vulnerable.
Symptoms and How the Disease Looks
One of the most dangerous features of CMV retinitis is that it can be asymptomatic at first. The infection typically begins in the peripheral retina, far from the center of vision, so you may not notice anything wrong until it has progressed significantly. When symptoms do appear, they often include floaters, blurred vision, blind spots, or flashing lights. As the disease advances toward the macula, the central area of the retina responsible for sharp vision, the risk of severe and permanent vision loss increases sharply.
On examination, the retina shows a distinctive pattern sometimes described as a “pizza pie” appearance: areas of white or yellowish retinal necrosis surrounded by hemorrhage. Mild vitreous inflammation at the onset can be an important clue that distinguishes CMV retinitis from other eye conditions in HIV patients.6PubMed Central. Cytomegalovirus Retinitis: Clinical Manifestations, Diagnosis and Treatment Without treatment, the infection relentlessly destroys more retinal tissue over weeks, eventually causing blindness. Early antiviral therapy significantly reduces that risk.
Diagnosis
Experienced ophthalmologists can often diagnose CMV retinitis by looking at the retina with a dilated eye exam, recognizing the characteristic pattern of necrosis and hemorrhage. But when the picture is unclear, or when other infections need to be ruled out, laboratory testing becomes critical. People with AIDS can develop retinitis from several different organisms, including toxoplasma, varicella-zoster virus, and herpes simplex virus, and distinguishing among them affects treatment choices.7The American Journal of Medicine. Differential diagnosis of retinitis and choroiditis in patients with acquired immunodeficiency syndrome
The most reliable laboratory tool is PCR testing of fluid from inside the eye. A small sample of aqueous humor (the clear fluid at the front of the eye) or vitreous fluid can be tested for CMV DNA. One study found that PCR detected CMV DNA in 18 of 19 eyes with untreated CMV retinitis, giving it about 95% sensitivity for active, untreated disease. It produced no false positives in patients without CMV retinitis, including those with vitreous inflammation from other causes.8PubMed. A sensitive and specific polymerase chain reaction-based assay for the diagnosis of cytomegalovirus retinitis The amount of CMV DNA in the fluid also correlates with how much active disease is present in the retina, making quantitative PCR useful for monitoring treatment response, and these ocular samples outperform blood-based tests for assessing retinal disease activity.9The Journal of Infectious Diseases. Cytomegalovirus (CMV) Retinitis Activity Is Accurately Reflected by the Presence and Level of CMV DNA in Aqueous Humor and Vitreous
PCR testing of vitreous samples has also proven valuable in diagnostically difficult cases, detecting CMV, varicella-zoster, or herpes simplex DNA in vitreous biopsies from patients whose clinical picture was initially ambiguous.10PubMed. Polymerase chain reaction-based assays of vitreous samples for the diagnosis of viral retinitis One limitation worth noting: in previously treated eyes, the sensitivity of PCR drops considerably, since antiviral drugs reduce the viral load. In patients already on ganciclovir or foscarnet, the sensitivity fell to about 48%.8PubMed. A sensitive and specific polymerase chain reaction-based assay for the diagnosis of cytomegalovirus retinitis
Antiviral Drug Treatment
The standard treatment for CMV retinitis uses antiviral medications, most commonly ganciclovir and its oral prodrug valganciclovir. Treatment has two phases: induction, where higher doses are given for two to three weeks to bring the infection under control, and maintenance, where a lower dose is continued long-term to prevent relapse.
Valganciclovir has largely replaced intravenous ganciclovir for most patients because it can be taken by mouth, which avoids the complications associated with long-term intravenous catheters. A controlled trial comparing the two found essentially identical outcomes: about 10% of patients in each group had disease progression during the first four weeks of treatment, and roughly three-quarters of patients in both groups had a satisfactory response to induction therapy. Adverse events were similar between the groups.11PubMed. A controlled trial of valganciclovir as induction therapy for cytomegalovirus retinitis
Long-term maintenance with valganciclovir carries real side effects. In a safety study with a median treatment duration of about a year, roughly a third of patients experienced diarrhea, about a quarter had nausea, and one in ten developed serious drops in white blood cell counts. Anemia occurred in about 12% of patients. Catheter-related complications, however, were uncommon at 6%, a clear advantage over intravenous ganciclovir.12JAIDS Journal of Acquired Immune Deficiency Syndromes. A Safety Study of Oral Valganciclovir Maintenance Treatment of Cytomegalovirus Retinitis Other antiviral options include foscarnet and cidofovir, which are typically reserved for patients who cannot tolerate ganciclovir or whose virus has become resistant to it.
Injections and Implants for the Eye
When the infection threatens the macula or optic nerve (a location known as zone 1), or when systemic drugs alone are not working fast enough, treatment can also be delivered directly into the eye. Intravitreal injections of ganciclovir or foscarnet place the drug right where it is needed, achieving high local concentrations that systemic treatment alone may not reach. International guidelines recommend weekly intravitreal ganciclovir injections for two to three weeks alongside systemic treatment in cases of immediately sight-threatening disease.13Open Forum Infectious Diseases. Cytomegalovirus Retinitis Screening and Treatment in Human Immunodeficiency Virus Patients in Malawi: A Feasibility Study
A more sustained approach involves a surgically implanted device that releases ganciclovir directly into the vitreous cavity over four to five months. In an early phase 1 study, all 13 eyes that received the implant showed resolution of active CMV retinitis with no further progression.14JAMA Ophthalmology. Sustained-Release Ganciclovir Therapy for Treatment of Cytomegalovirus Retinitis: Use of an Intravitreal Device The implant offers clear advantages over repeated injections, but it only protects the implanted eye and does nothing to prevent CMV disease elsewhere in the body, so systemic treatment is still needed alongside it.15PubMed Central. Optimal management of cytomegalovirus retinitis in patients with AIDS
When the Immune System Recovers
The introduction of effective antiretroviral therapy for HIV changed the entire landscape of CMV retinitis. The incidence of new cases dropped sharply, and survival improved from a median of about eight months before 1995 to over a year afterward. Among patients receiving antiretroviral therapy, none experienced disease progression after six months of treatment.16AIDS. Changes in the natural history of cytomegalovirus retinitis following the introduction of highly active antiretroviral therapy
As CD4+ counts rise with antiretroviral therapy, the immune system regains the ability to control CMV on its own. This has allowed clinicians to safely stop maintenance antiviral drugs in patients whose retinitis is stable and whose immune recovery is sustained. One study found that patients with CD4+ counts above 75 cells per microliter who had been on antiretroviral therapy for at least 18 months could safely discontinue CMV maintenance treatment.17PubMed. Discontinuation of maintenance therapy for cytomegalovirus retinitis in HIV-infected patients receiving highly active antiretroviral therapy A separate study confirmed that stopping anti-CMV medications was safe in patients with elevated CD4+ counts and stable retinitis, demonstrating that immune recovery is genuinely effective at controlling this major opportunistic infection.18JAMA. Discontinuation of Anticytomegalovirus Therapy in Patients With HIV Infection and Cytomegalovirus Retinitis Ongoing monitoring remains essential, since a drop in CD4+ counts from treatment interruption or drug resistance can allow the virus to reactivate.
Immune Recovery Uveitis
Paradoxically, one of the most common complications of CMV retinitis in the modern treatment era comes not from the virus itself but from the immune system bouncing back. Immune recovery uveitis (IRU) is an inflammatory reaction inside the eye that occurs when the recovering immune system mounts a vigorous response against residual CMV antigens in the retina. It is the most common form of immune reconstitution inflammatory syndrome affecting the eye in HIV patients with a history of CMV retinitis.19PubMed Central. Immune recovery uveitis: pathogenesis, clinical symptoms, and treatment
IRU manifests with inflammation of the vitreous, swelling of the optic disc, and macular edema, which is the main threat to vision. It can also cause epiretinal membrane formation and cataracts.20PubMed. Immune-recovery uveitis in patients with cytomegalovirus retinitis taking highly active antiretroviral therapy The condition presents a clinical dilemma: you want the immune system to recover because that controls the virus, but the recovering immune system can create new inflammation that damages vision. Treatment typically involves corticosteroids, either topical or injected around the eye, to dampen the inflammatory response while allowing the immune recovery to continue.21PubMed Central. Immune recovery uveitis: a focus review
Retinal Detachment
Even after the infection is brought under control, the structural damage CMV leaves behind creates lasting vulnerability. The necrotic retinal tissue is thin and fragile, prone to developing holes that allow fluid to seep underneath and peel the retina away from its supporting layers. Retinal detachment is one of the most feared complications, and it occurred frequently in the pre-antiretroviral era when patients survived long enough with extensive retinal scarring.
Surgical repair typically involves vitrectomy (removing the vitreous gel) and filling the eye with silicone oil to hold the retina in place. A large multicenter study found that at six months after surgery, the retina was completely reattached in about 78% of CMV-related eyes, and roughly two-thirds of those patients maintained useful ambulatory vision.22PubMed. Silicone oil in the repair of complex retinal detachments. A prospective observational multicenter study Research has also shown that scleral buckling, an additional step in traditional detachment repair, may not be necessary when vitrectomy with silicone oil and laser treatment is used, potentially reducing operative time and patient discomfort.23PubMed. Results of rhegmatogenous retinal detachment repair in cytomegalovirus retinitis with and without scleral buckling A smaller study looking at outcomes after silicone oil removal reported an anatomical success rate of about 82%, meaning the retina stayed attached after the oil was taken out.24PubMed Central. Results of silicone oil removal in post-cytomegalovirus retinitis-related retinal detachment
Drug Resistance
Long-term antiviral therapy creates the conditions for the virus to evolve resistance. Ganciclovir-resistant CMV is a real clinical problem. Resistance often involves mutations in the viral UL97 gene, which encodes the enzyme that activates ganciclovir inside infected cells. One study examining vitreous fluid from eyes that had not responded to ganciclovir therapy found known resistance mutations in about half of the cases tested.25PubMed. Mutations in the cytomegalovirus UL97 gene associated with ganciclovir-resistant retinitis That not all unresponsive eyes showed resistance mutations suggests that treatment failure can also stem from insufficient drug delivery to the retina or other factors beyond simple genetic resistance.
When ganciclovir resistance is confirmed or suspected, clinicians typically switch to foscarnet or cidofovir, which target the virus through different mechanisms. Both drugs come with their own toxicity profiles, including kidney damage with cidofovir and electrolyte disturbances with foscarnet, so managing resistant CMV retinitis is a balancing act between viral control and drug side effects.
CMV Retinitis in Children
Though the disease is most associated with adults living with HIV, children are not immune. CMV retinitis has been documented in children with a range of immune-compromising conditions, from severe combined immunodeficiency to leukemia to organ transplantation. A case series found nine immunocompromised children with CMV retinitis, and the disease was bilateral in 89% of them and involved the posterior pole (the area near the macula) in every single child. Strikingly, only two of the nine children had reported any visual symptoms at diagnosis.26PubMed. Cytomegalovirus retinitis in immunosuppressed children The mortality rate was alarming: four of the nine children died within ten months of their CMV retinitis diagnosis.
Children pose a particular diagnostic challenge because they are less likely to report vision problems, especially younger children who may not notice or be able to describe changes in their sight. One report noted that among immunosuppressed children over three years old with advanced bilateral disease, none had subjective visual complaints.27Pediatric Hematology Oncology Journal. Bilateral cytomegalovirus retinitis in a child with acute lymphoblastic leukemia while on maintenance chemotherapy This means the disease often reaches an advanced stage before anyone realizes it is there, making a strong case for proactive retinal screening in severely immunocompromised children rather than waiting for the child to complain about their vision.
Access to Treatment Around the World
In wealthy countries, CMV retinitis has become far less common and far more manageable since effective HIV treatment became widely available. In resource-limited settings, the picture is very different. Patients presenting with advanced HIV and profoundly low CD4+ counts still develop CMV retinitis, sometimes as the first sign that they are infected with HIV at all. And when it is recognized, adequate treatment is often out of reach.
Valganciclovir is on the WHO’s Model List of Essential Medicines for CMV retinitis, and generic versions exist. Yet in many low-income countries the price remains prohibitively high and access is severely limited. A feasibility study in Malawi highlighted this gap: even when CMV retinitis was identified, treatment was often inadequate because the drugs simply were not available. The authors noted that if valganciclovir prices were to fall substantially, it could transform how the disease is managed, since oral valganciclovir can be administered in community settings without the need for intravenous access or hospital admission.13Open Forum Infectious Diseases. Cytomegalovirus Retinitis Screening and Treatment in Human Immunodeficiency Virus Patients in Malawi: A Feasibility Study Until affordable antiviral access improves, CMV retinitis will continue to cause preventable blindness in exactly the populations that are already hardest hit by HIV.