Cytomegalovirus Retinitis
A devastating viral eye infection causing retinal destruction and blindness, occurring in severely immunocompromised patients, particularly those with advanced HIV/AIDS.
Emergency Management: Zone 1 CMV Retinitis threatening the macula requires emergency same-day evaluation by a retina specialist for intravitreal antiviral injection to save central vision. Retinal detachment requires urgent surgery.
Cytomegalovirus (CMV) retinitis is a severe, sight-threatening, full-thickness opportunistic viral infection of the retina caused by the reactivation of latent cytomegalovirus (Human Herpesvirus 5). It occurs almost exclusively in severely immunocompromised individuals, classically patients with advanced AIDS or organ transplant recipients.
Detailed Overview
CMV is a ubiquitous virus that establishes lifelong latency after primary infection. In the setting of profound cellular immunodeficiency (specifically CD4+ T-cell depletion), the virus reactivates and hematogenously spreads to the retina. It causes necrotizing retinitis, presenting with characteristic hemorrhagic and exudative lesions. If left untreated, the progressive necrosis inevitably destroys the macula and optic nerve, or causes retinal detachment, leading to irreversible total blindness. The advent of highly active antiretroviral therapy (HAART) has drastically reduced its incidence.
Epidemiology & Demographics
Historically affected up to 30% of AIDS patients before the HAART era. Currently, incidence in the US is low but remains a significant threat in patients unaware of their HIV status or non-compliant with HAART, specifically when CD4 count falls below 50 cells/microL.
Etiological Mechanism
Reactivation of latent Cytomegalovirus (CMV).
Primary Causes
Untreated or advanced HIV infection with severe CD4 depletion
Iatrogenic immunosuppression following solid organ or hematopoietic stem cell transplantation
In severe immunodeficiency, latent CMV in monocytes/macrophages reactivates. The virus reaches the eye via the retinal vasculature. It initially infects the vascular endothelial cells, causing a vasculitis, and then spreads to the glial cells and retinal pigment epithelium (RPE). The virus replicates within these cells, causing cytopathic cell death (necrosis). Because the retina cannot regenerate, the destroyed tissue leaves behind a thin, atrophic glial scar. The active leading edge of infection slowly expands outward. The resultant full-thickness necrosis weakens the retina, making it highly susceptible to rhegmatogenous retinal detachment. Furthermore, immune recovery upon starting HAART can trigger a paradoxically destructive inflammatory response known as Immune Recovery Uveitis (IRU).
Diagnostic Criteria & Guidelines
Diagnosis is primarily clinical, based on the characteristic fundoscopic appearance (hemorrhage + necrosis) in a severely immunocompromised patient. PCR of aqueous or vitreous fluid for CMV DNA can confirm atypical cases.
Induction therapy is required. For Zone 1 (sight-threatening) lesions: Immediate Intravitreal Injection of Ganciclovir (2 mg/0.05 mL) or Foscarnet (2.4 mg/0.1 mL) 1-2 times weekly, PLUS Systemic Valganciclovir 900 mg PO BID for 14-21 days. For peripheral lesions (Zone 2/3): Systemic Valganciclovir 900 mg PO BID alone for 14-21 days.
Second-Line & Adjunctive Therapy
If resistance or toxicity (Valganciclovir causes severe neutropenia): IV Ganciclovir 5 mg/kg every 12h, IV Foscarnet 90 mg/kg every 12h (nephrotoxic), or IV Cidofovir (requires probenecid and saline hydration). Foscarnet or Cidofovir are typically used for UL97-mutant (ganciclovir-resistant) CMV.
Surgical & Procedural Management
Pars plana vitrectomy with endolaser photocoagulation and silicone oil tamponade is required for CMV-associated retinal detachment.
Patient Counseling & Advice
Inform the patient that while medication halts the spread of the virus, the areas of the retina already destroyed cannot regenerate, and any lost vision is permanent. Emphasize that they must stay on maintenance anti-CMV therapy until their CD4 count recovers above 100 on HAART, otherwise the infection will definitely return.
Follow-Up & Monitoring Schedule
Weekly dilated fundus exams by an ophthalmologist during induction, then every 2-4 weeks during maintenance therapy. Routine CBC and CMP to monitor for ganciclovir-induced bone marrow suppression and foscarnet-induced renal failure.
Preventive Strategies
In HIV patients: Early initiation of HAART to prevent CD4 drop. Routine dilated eye exams every 6 months for any patient with CD4 < 50. Primary prophylaxis with oral valganciclovir is no longer routinely recommended due to toxicity, preferring early HAART instead.
Highly dependent on the location of the lesion at the time of diagnosis and the patient's ability to reconstitute their immune system via HAART. Retinitis progression is typically halted within 2 weeks of starting antivirals.