Acute retinal necrosis (ARN) is a rare viral infection causing severe inflammation and damage to the retina, the light-sensitive layer at the back of the eye. As its name suggests, ARN has an acute onset, appearing suddenly and progressing rapidly. Without immediate medical attention, it can lead to significant and permanent vision loss.
Causes and Symptoms of ARN
ARN is caused by a reactivation of viruses from the herpes family. The most common culprit is the varicella-zoster virus (VZV), the same virus responsible for chickenpox and shingles. Herpes simplex virus (HSV), types 1 and 2, are also frequent causes. These viruses can reactivate in the eye years after the initial infection, and it is not fully understood why some individuals develop ARN while others do not. The condition affects healthy individuals, often between the ages of 50 and 70, but can also occur in those with compromised immune systems.
The initial symptoms develop quickly in one eye and can be mistaken for less serious conditions. A person may first notice a sudden increase in floaters (small specks drifting through their vision) and flashes of light. Vision becomes progressively blurred, and there may be associated eye pain, redness, and sensitivity to light. Although ARN begins in a single eye, there is a risk the infection can spread to the other, especially if treatment is delayed.
The Diagnostic Process
An ophthalmologist diagnoses acute retinal necrosis based on a clinical examination of the eye’s interior. During this exam, the doctor looks for a combination of signs characteristic of the condition. These findings include inflammation within the vitreous (the gel-like substance that fills the eye) and of the retinal blood vessels, a condition called occlusive vasculitis. The most definitive sign is retinal necrosis, where patches of retinal tissue appear whitened and damaged.
To confirm the diagnosis and identify the specific virus, a physician may collect a small sample of fluid from inside the eye. This fluid, either from the aqueous or vitreous humor, is then analyzed. A polymerase chain reaction (PCR) test is used to detect the presence of viral DNA, such as VZV or HSV. This confirmation helps guide treatment, though therapy is often started immediately based on clinical findings due to the disease’s rapid progression.
Medical and Surgical Treatments
The primary goal of medical therapy for ARN is to halt the viral replication process. Treatment is initiated immediately upon suspicion of the diagnosis. This involves administering high-dose antiviral medications, given intravenously (IV) in a hospital setting. After an initial period of IV treatment, which may last from five to ten days, patients are transitioned to high-dose oral antiviral pills for several more weeks to prevent a recurrence.
In addition to antiviral drugs, corticosteroids like prednisone are used to manage the severe inflammation associated with ARN. However, these are started only after the antiviral medication has begun to control the infection, to avoid suppressing the immune response too early. Some patients may also receive antiviral medications injected directly into the eye, particularly if the inflammation threatens the central part of the retina or the optic nerve.
Surgical intervention is not used to cure the viral infection but to manage or prevent its complications, most notably retinal detachment. A procedure called prophylactic laser photocoagulation may be performed to create a barrier of burns around the necrotic retina. This helps prevent it from detaching as the damaged tissue thins. If a retinal detachment has already occurred, a vitrectomy is required to remove the vitreous gel and reattach the retina.
Prognosis and Long-Term Complications
The visual prognosis for individuals with ARN is variable and depends on the extent of retinal damage and the timeliness of treatment. Even with aggressive medical intervention, some degree of permanent vision loss is common. The final visual outcome is determined by which parts of the retina were affected and whether complications arise. Early diagnosis and immediate antiviral therapy can improve the overall visual prognosis.
The most significant long-term complication of ARN is retinal detachment, which can occur weeks or months after the initial infection has resolved. The necrotic retinal tissue becomes thin and fragile, making it susceptible to tears that allow fluid to lift the retina away from the back of the eye. This is a leading cause of severe vision loss in patients who have had ARN. Because of this risk, long-term monitoring by an ophthalmologist is necessary.