Acute Retinal Necrosis

Acute retinal necrosis (ARN) is a rapidly progressive, necrotising retinitis caused by the herpes viruses, mainly varicella zoster virus (over 50 percent, in older patients), herpes simplex virus type 1 (older and younger adults) and type 2 (younger patients, history of neonatal or meningitis), and rarely cytomegalovirus and Epstein-Barr virus.

• Occurs in healthy and immunocompromised individuals; bilateral in about 33 percent (fellow eye often affected within weeks to months if untreated).
• Often follows herpetic encephalitis, meningitis, zoster or herpes labialis in the preceding weeks to years.
• Characterised by peripheral necrotising retinitis, occlusive retinal vasculitis, and vitritis. Retinal detachment occurs in 50 to 75 percent within the first months due to multiple posterior retinal breaks at the border of necrosis.
• Progressive outer retinal necrosis (PORN) is a rapidly progressive form in profound immunosuppression (HIV with CD4 under 50), with minimal inflammation and early macular involvement.

• Eye pain, redness, floaters, blurred vision, field defect; anterior uveitis with granulomatous keratic precipitates.
• Peripheral multifocal, well demarcated patches of white yellow retinal necrosis that coalesce circumferentially, with arteriolar occlusive vasculitis, vitritis, optic disc oedema and optic neuropathy.
• Late: retinal atrophy with pigmented borders, retinal breaks and detachment, proliferative vitreoretinopathy, phthisis.
• Systemic: history of cutaneous zoster or herpetic encephalitis; the patient may be well.

• Clinical, based on peripheral necrotising retinitis progressing quickly, with occlusive vasculitis and prominent vitritis, in the context of herpetic features. Diagnostic criteria require peripheral lesions, circumferential spread, vascular occlusion, and a prominent inflammatory reaction, with rapid progression in the absence of therapy.
• Aqueous or vitreous polymerase chain reaction for varicella zoster, herpes simplex 1 and 2, cytomegalovirus (aqueous sensitivity about 90 percent); do not delay treatment while awaiting results.
• HIV test and other immune status assessment; MRI brain and cerebrospinal fluid analysis if neurological symptoms (herpes simplex encephalitis risk).
• Fluorescein angiography (occlusive vasculitis), optical coherence tomography, and B-scan.

• Start antivirals immediately on clinical suspicion:
  • Intravenous aciclovir 10 mg/kg every 8 hours (500 mg/m2) for 10 to 14 days, with hydration and renal monitoring; then oral valaciclovir 1 g three times daily (or famciclovir 500 mg three times daily) for 6 to 14 weeks (total up to 3 months), to prevent fellow eye disease and relapse.
  • Intravitreal ganciclovir 2 mg in 0.05 mL (or foscarnet 2.4 mg in 0.1 mL), twice weekly for 1 to 2 doses, reduces progression and speeds recovery; added to systemic therapy for severe or macular threatening disease.
  • Resistant disease: foscarnet 90 mg/kg every 12 hours intravenously.
• Corticosteroids after 24 to 48 hours of antivirals: oral prednisolone 1 mg/kg daily for 1 to 2 weeks, tapered, and topical prednisolone acetate 1 percent with atropine 1 percent for anterior inflammation.
• Antithrombotic therapy: aspirin 75 to 100 mg daily has been used for occlusive vasculitis, without proven benefit.
• Prophylactic 360-degree laser retinopexy posterior to the necrosis (3 to 4 rows) when the view allows, to reduce detachment, with the caution that the vitreous haze can limit laser.
• Retinal detachment: pars plana vitrectomy with silicone oil (or gas), endolaser and sometimes encircling buckle, with antiviral cover.
• Long term prophylaxis: oral valaciclovir 500 mg to 1 g daily or aciclovir 400 to 800 mg twice daily for 6 months to years, particularly in immunosuppressed patients, to prevent second eye disease (risk about 65 percent without therapy).
• Follow closely (every few days at first), then weekly, with fellow eye examination at each visit. Counsel regarding urgent symptoms.