A 45-year-old healthy man develops floaters and rapidly worsening vision in his right eye over one week, with mild ache. Fundus examination reveals confluent yellow-white necrosis sweeping around the peripheral retina with sheathed, occluded arterioles and vitritis. The left eye is currently normal.
Examination Findings
Visual acuity: 6/60 right, 6/6 left. Right fundus: confluent peripheral yellow-white necrotising retinitis sweeping circumferentially, occlusive retinal arteritis with sheathing, moderate vitritis, early optic disc hyperaemia. Anterior segment shows mild cells. Onset was one week of floaters and vision loss, now accelerating. He is otherwise healthy with no immunosuppression.
Investigations
Dilated fundus examination with scleral depression maps the full circumferential extent of the necrosis — the periphery must be seen. The fellow eye is examined carefully, as the second eye often follows. Aqueous or vitreous PCR for herpes viruses confirms the cause where available, but treatment starts on clinical suspicion without delay.
Questions to Think About
- What triad of findings defines acute retinal necrosis?
- Why must treatment start before laboratory confirmation?
- What is the commonest blinding complication to watch for after the acute phase?
Diagnosis
Acute retinal necrosis: rapidly progressive peripheral confluent necrotising retinitis with occlusive retinal arteritis and vitritis — a viral retinal emergency.
Reasoning
Reasoning: Rapidly progressive confluent peripheral necrotising retinitis with occlusive retinal arteritis and vitritis in an immunocompetent adult is acute retinal necrosis, typically from herpes simplex or varicella-zoster virus. CMV is excluded by the competent immunity and rapid confluent pattern; toxoplasma by the absence of a scar. Diagnosis: acute retinal necrosis, right eye. Management: typical management includes immediate systemic antivirals per local protocol without waiting for PCR, specialist retinal surveillance for detachment, and fellow-eye monitoring. He is told of the viral cause, the urgency, and the detachment risk.
Differential Diagnosis
- CMV retinitis — ruled out: he is immunocompetent with no HIV; the necrosis is rapidly confluent and peripheral with occlusive arteritis, not indolent granular perivascular disease.
- Toxoplasma chorioretinitis — ruled out: no old scar with satellite lesion; the disease is multifocal peripheral necrosis with vasculitis.
- Behçet retinal vasculitis — ruled out: no oral/genital ulcers, no hypopyon; the dominant lesion is confluent retinal necrosis, not vasculitis alone.
Management
Typical management includes immediate high-dose systemic antiviral therapy per local protocol, started on clinical diagnosis, with urgent vitreoretinal specialist input for detachment surveillance and possible prophylactic laser to the necrotic borders. The fellow eye is watched closely. He is told a herpes-family virus is destroying the peripheral retina, that immediate treatment aims to halt it, and that retinal detachment checks continue for months.
Key Learning Points
- Confluent PERIPHERAL necrosis + occlusive arteritis + vitritis in a healthy adult is acute retinal necrosis — usually herpes viruses.
- It moves FAST: days matter, and the fellow eye is at high risk — examine and protect both.
- Start systemic antivirals on suspicion; do not wait for PCR — the retina necroses while you wait.
- Retinal detachment is the common blinding sequel: the necrotic retina tears, so detachment surveillance is mandatory.
- Corticosteroids come only WITH antivirals and specialist direction — never alone in ARN.
Red Flags
- Confluent peripheral necrosis with arteritis — start systemic antivirals immediately; this is an emergency.
- New flashes, floaters or a shadow in ARN — the necrotic retina is detaching.
- Fellow-eye floaters or peripheral whitening — the second eye is involved; treat it too.
Educational content only — not medical advice. Clinical decisions must be made by a qualified professional for the individual patient.
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