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Acute Retinal Necrosis: Recognizing and Treating a Retinal Emergency
Understanding Acute Retinal Necrosis
ARN is a well-defined clinical condition with specific, recognizable features. Understanding what the disease is and how it behaves helps explain why early action is so important.
Acute retinal necrosis is a rapidly progressive retinitis, meaning a viral infection that causes inflammation and death of retinal tissue. It is defined by a set of clinical criteria established by the American Uveitis Society. Those criteria include one or more areas of peripheral retinal necrosis (tissue death in the outer retina) with clearly defined borders, rapid circumferential spread of the necrosis without antiviral treatment, occlusive vasculopathy (blockage and inflammation of the retinal blood vessels), and prominent intraocular inflammation affecting both the vitreous (the gel-like fluid inside the eye) and the anterior chamber (the fluid-filled space in front of the lens).
ARN was first recognized as a distinct disease entity in the 1970s. It is rare, with an estimated incidence of less than one case per million people per year, but its capacity for rapid and irreversible vision loss makes it one of the most urgent conditions we manage in retinal care.
ARN is caused by the reactivation of a virus from the herpes family that the patient has already been carrying in their body, often for years or decades without any symptoms.
- Varicella-zoster virus (VZV), the same virus that causes chickenpox and shingles, is the most common cause of ARN and tends to affect older adults
- Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) are the second most common cause and are more often seen in younger patients
- Cytomegalovirus (CMV) and Epstein-Barr virus have been identified as less frequent but recognized causes
The virus remains dormant in the nervous system after the original infection, sometimes for decades, before reactivating and traveling to the retina. ARN can develop in people with healthy immune systems as well as those with weakened immune defenses.
The virus directly kills retinal cells, producing areas of full-thickness necrosis, meaning the destruction extends through the entire depth of the retina rather than affecting only the surface layers. The infection typically begins in the peripheral (outer) retina and, if untreated, spreads inward in a circumferential pattern that can eventually threaten the central vision area.
At the same time, the infection triggers an intense immune response. This produces vasculitis (inflammation of the retinal arteries), which can block blood flow and cause additional ischemic damage from oxygen deprivation. As the necrotic retina heals over time, it becomes thin, fragile, and prone to tearing. Vitreous traction, the pulling force of the vitreous gel on this weakened tissue, is the primary mechanism behind retinal detachment, which is the most serious complication of ARN. Retinal detachment develops in an estimated 50 to 75 percent of ARN cases, with most occurring within the first three months of onset.
Who Can Develop ARN?
ARN can affect virtually anyone who has been previously infected with a herpes family virus. While rare, the condition does not discriminate by age, sex, or health status, although certain factors can increase the risk of viral reactivation and retinal involvement.
ARN most commonly affects otherwise healthy adults without any identified immune deficiency. It can occur at any age, from children to older adults, and is seen in both men and women across all ethnic groups. Because herpes family viruses are widespread in the general population and often acquired during childhood, most adults already carry the latent viruses that can cause ARN. Only a very small proportion will ever experience retinal reactivation, but the unpredictability of that risk makes awareness of symptoms important for everyone.
Certain circumstances are known to raise the likelihood of herpes virus reactivation and retinal involvement.
- A weakened immune system, whether from HIV infection, organ transplantation, or chemotherapy, significantly increases the risk of severe or unusual herpes reactivation
- A personal history of shingles, chickenpox complications, or recurrent herpes simplex outbreaks indicates prior viral exposure and the presence of latent virus
- Some patients have no recognized history of prior herpes infection because their original exposure produced no noticeable symptoms at the time
Even patients who are otherwise healthy and have no obvious risk factors can develop ARN. This reinforces why these symptoms should never be dismissed or managed with a wait-and-see approach.
Recognizing the Signs of ARN
ARN produces a distinctive and rapidly evolving set of symptoms and examination findings. Knowing what to watch for is essential because the window for effective early treatment can be very narrow.
ARN typically begins suddenly in one eye. The most common early symptoms include blurred vision, eye pain, redness, and sensitivity to light (photophobia). New floaters, spots or shadows drifting across the visual field, are also common because of intense inflammation in the vitreous. Some patients report headache or periorbital pain (pain around the eye socket) in the days surrounding onset.
Visual acuity may be only mildly reduced at first, which can create a false sense of reassurance. However, vision can deteriorate quickly as the retinal necrosis advances. Any combination of sudden eye pain, redness, light sensitivity, and new floaters should be treated as a potential emergency until proven otherwise.
When we examine an eye affected by ARN, several characteristic findings guide the diagnosis. The anterior chamber shows significant inflammation, with cells and protein haze visible under the slit lamp (a specialized microscope used to examine the eye). The vitreous is clouded by inflammatory cells, reducing clarity inside the eye. The hallmark finding is one or more patches of white or yellow retinal necrosis in the peripheral retina with sharp, clearly defined borders.
Retinal arteritis, visible as white sheathing along the walls of the retinal arteries, accompanies the necrosis. Without treatment, the necrotic patches expand circumferentially around the retina and can progress toward the macula (the central vision area). The optic nerve may appear swollen as well.
Yes. Bilateral involvement is a recognized risk of ARN, with the second eye potentially becoming affected weeks to months after the first. This is one of the primary reasons systemic (whole-body) antiviral treatment is essential, rather than relying on local treatment alone. Systemic therapy works to suppress viral reactivation in the fellow eye as well as the eye already affected.
Any new visual symptoms in the unaffected eye, even mild blurring or a few new floaters, should prompt an immediate call to your retinal specialist. Fellow eye involvement requires urgent re-evaluation and may call for intensifying the overall treatment plan.
How ARN Is Diagnosed
Confirming the diagnosis of ARN quickly is as important as any other step in management. We use a combination of clinical examination, laboratory testing, and specialized retinal imaging to evaluate the condition and guide individualized treatment decisions.
The diagnosis of ARN is primarily a clinical one, based on the characteristic appearance of the eye during examination using the criteria from the American Uveitis Society. The combination of peripheral retinal necrosis, retinal vascular inflammation, and significant intraocular inflammation often creates a presentation that is recognizable enough to begin antiviral treatment immediately, before any laboratory results are available. In ARN, waiting for confirmatory tests before starting treatment can allow the retina to sustain additional irreversible damage. A high index of suspicion and a willingness to act quickly are essential.
Polymerase chain reaction (PCR) testing is the standard confirmatory laboratory test for ARN. A small sample of fluid is collected from inside the eye, either from the aqueous humor in the front of the eye through a procedure called an aqueous tap, or from the vitreous through a small needle. PCR testing identifies the specific herpes virus responsible for the infection with high accuracy.
Knowing the causative virus can help guide decisions about antiviral medication selection and treatment duration. However, treatment is initiated on clinical grounds before PCR results return. Confirmation is helpful, but it does not replace the need for immediate action.
Specialized imaging tools help us assess the extent of retinal involvement, monitor treatment response, and detect complications early.
- Wide-field fundus photography captures a broad view of the retina, documenting the location and extent of necrotic areas at diagnosis and tracking changes at follow-up visits
- Fluorescein angiography uses an intravenous dye to highlight the retinal blood vessels, revealing areas of vascular occlusion and nonperfusion caused by the arteritis
- Optical coherence tomography (OCT) provides detailed cross-sectional images of the retina, showing thickening in areas of active infection, subretinal fluid, and structural changes over time
Serial imaging at each follow-up visit allows us to determine whether the necrosis is stabilizing in response to treatment or continuing to advance, and to identify early signs of retinal detachment before it becomes complete.
Treating Acute Retinal Necrosis
Effective ARN treatment requires a coordinated, multi-layered approach. Antiviral medications form the foundation, anti-inflammatory therapy addresses secondary damage, and surgery may be necessary if retinal detachment develops. Every element of the plan is individualized based on the severity of the infection, the patient's immune status, and the specific virus involved.
Immediate systemic antiviral therapy is the cornerstone of ARN treatment. Oral valacyclovir at high doses is the preferred induction regimen for many patients because it achieves effective blood levels and can be taken at home. For more severe presentations or immunocompromised patients, intravenous acyclovir may be used first to achieve the highest possible drug concentrations as rapidly as possible.
Systemic antiviral treatment serves two simultaneous goals. It works to stop the progression of retinal necrosis in the affected eye, and it helps protect the fellow eye from viral reactivation. Treatment continues for an extended period, typically transitioning from a high induction dose to a lower maintenance dose once the acute phase resolves. The duration and dosing are determined by the treating retinal specialist based on individual factors.
Intravitreal injections, medications delivered directly into the vitreous cavity of the eye, are frequently used alongside systemic antiviral therapy for ARN. Foscarnet and ganciclovir are the antiviral agents most commonly used for intravitreal injection in this setting. Delivering medication inside the eye achieves drug concentrations at the site of infection that cannot be reached through oral or intravenous routes alone.
Research has shown that combining systemic antiviral therapy with intravitreal injections is associated with meaningfully lower rates of retinal detachment compared to systemic treatment by itself. Because of this evidence, the combined approach has become the standard of care at specialized retina centers. Injections may be administered repeatedly during the acute phase to maintain maximum viral suppression until the infection is under control.
ARN causes severe intraocular inflammation that can damage ocular structures independently of the viral destruction itself. Systemic corticosteroids (anti-inflammatory steroid medications) may be added to the treatment plan to reduce vitreous haze, manage vascular inflammation, and help control the overall inflammatory burden on the eye.
The timing of corticosteroid use is critically important. Steroids must not be started before adequate antiviral therapy is established and the infection is being actively controlled. Beginning immunosuppression without antiviral protection in place could allow the virus to replicate more aggressively. We coordinate the introduction of corticosteroids carefully and monitor the eye's response closely throughout the process.
Prophylactic laser photocoagulation is sometimes applied to the healthy retina at the posterior border of the necrotic zone. By creating a ring of treated, adherent tissue around the area of necrosis, laser treatment may help contain the spread of any retinal detachment that develops as the necrotic tissue heals and thins. This approach is not appropriate for every patient and the decision is made on an individual basis.
When retinal detachment does occur, surgical intervention is necessary. Pars plana vitrectomy (surgery to remove the vitreous gel and repair retinal tears from inside the eye) combined with silicone oil tamponade (the use of silicone oil to hold the retina against the eye wall during healing) is the most commonly used surgical approach for ARN-related detachments. This surgery is technically demanding because the necrotic and atrophic retinal tissue is extremely fragile. Our fellowship-trained vitreoretinal surgeons have the specialized skills and experience that these complex cases require.
What to Expect During and After Treatment
ARN requires sustained commitment to care over weeks and months. Understanding what recovery looks like can help patients stay engaged, adhere to treatment, and remain alert to warning signs throughout the process.
During the first weeks of treatment, the primary goal is to arrest the spread of retinal necrosis and bring the intraocular inflammation under control. With effective antiviral therapy, the active white patches of necrosis typically stop expanding. Over time, those areas gradually transition from a white or yellow active appearance to a pigmented, atrophic (thinned) scar as the infected tissue heals. The vitreous and anterior chamber inflammation gradually improve as well, and vision may begin to stabilize.
Frequent office visits are necessary during this phase. We monitor for signs of disease progression, assess the treatment response, and administer intravitreal injections on the appropriate schedule. Consistent adherence to the oral antiviral medication regimen is equally critical and must not be interrupted without guidance from your retinal specialist.
The period of greatest retinal detachment risk extends over the first several months after ARN onset. As the necrotic retina heals into thin, fragile scar tissue, vitreous traction on that weakened surface can create tears that lead to detachment. This risk persists even after the viral infection has been controlled and the acute inflammatory phase has resolved.
We monitor carefully for early signs of detachment at every follow-up visit using examination and imaging. If you develop any sudden new floaters, flashes of light, or a shadow or curtain in your vision, contact us immediately. These symptoms warrant same-day urgent evaluation and should not be attributed to normal post-treatment changes without assessment by your retinal specialist.
The visual prognosis after ARN varies considerably from patient to patient. It depends on how much retina was involved before treatment began, whether the macula was spared, whether retinal detachment occurred, and how successfully any detachment was repaired. Patients who receive prompt treatment, avoid retinal detachment, and have limited macular involvement have the best opportunity to retain meaningful functional vision.
Some patients achieve good visual recovery, particularly when the central retina is not affected. Others may experience lasting visual impairment when extensive retinal necrosis, optic nerve damage, or complicated retinal detachment has occurred despite appropriate treatment. Long-term follow-up continues after the acute phase to watch for recurrence, fellow eye involvement, and any late structural complications. Your retinal specialist will establish a monitoring schedule tailored to your individual situation and risk profile.
Frequently Asked Questions
The following answers address questions our patients often ask about ARN that go beyond what is covered in the sections above, including guidance on when to seek urgent care and how to navigate key decisions during treatment and follow-up.
ARN itself is not contagious from person to person. The condition results from reactivation of a virus already dormant inside the patient's own body, not from exposure to someone else with ARN. The herpes viruses that cause ARN, such as varicella-zoster and herpes simplex, can be transmitted between people through ordinary routes during an active outbreak elsewhere on the body, but ARN as a retinal disease is an internal reactivation event, not something that can be caught through contact with a person who has ARN. Standard hygiene precautions for any herpes virus apply, but there is no need to isolate yourself from family or household contacts specifically because of an ARN diagnosis.
The same day, if at all possible. ARN is an ophthalmic emergency in which hours matter. Retinal necrosis can advance within days without antiviral treatment, destroying tissue that cannot regenerate or be recovered. If you develop sudden painful blurred vision, redness, light sensitivity, and new floaters in one eye, seek evaluation at a retina specialty practice or emergency eye care facility right away. Do not wait to see if symptoms improve on their own. The speed of diagnosis and treatment initiation is one of the most significant factors affecting visual outcome in ARN.
Recurrence is possible. Because ARN is caused by a latent virus that remains in the body even after the acute infection is controlled, there is an ongoing risk of reactivation. Stopping maintenance antiviral therapy too soon increases that risk, and recurrence in the same eye or new involvement of the fellow eye are both possible. This is why your retinal specialist may recommend an extended course of maintenance dosing and why regular follow-up remains important long after the acute phase ends. Early detection of recurrence allows for rapid treatment intensification before additional retinal damage occurs.
ARN-related retinal detachment requires prompt surgical repair. Because the detachment typically involves multiple tears in fragile, necrotic retinal tissue, the standard approach is pars plana vitrectomy with silicone oil tamponade. The silicone oil is placed inside the eye temporarily to hold the retina against the eye wall during healing and is usually removed in a separate procedure once sufficient healing has occurred. Surgery for ARN-related detachment is among the most technically demanding in vitreoretinal surgery, and final visual outcomes depend on factors including whether the macula was detached, for how long, and the extent of prior retinal damage from the necrosis itself.
Contact your retinal specialist the same day you notice any new symptoms in the unaffected eye, even if they seem mild. Bilateral ARN can develop weeks to months after the first eye was affected, and early treatment gives the second eye the best opportunity to preserve vision. Do not wait for a scheduled appointment if you notice new floaters, blurring, light sensitivity, or pain in the fellow eye. This is an urgent situation that warrants same-day evaluation and may require an adjustment to your current antiviral regimen.
Expert Retinal Care When It Matters Most
New England Retina Associates is a retina-only practice with fellowship-trained vitreoretinal surgeons who specialize in the diagnosis and treatment of serious retinal conditions throughout Connecticut, including sight-threatening emergencies like acute retinal necrosis. We welcome both referred patients and those who contact us directly, and we are prepared to act quickly when vision is at risk. If you or someone you know is experiencing symptoms that may indicate ARN or another urgent retinal condition, please reach out to our team right away.
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