Evolution of the Onion Ring Sign in Radiation Retinopathy

A 53-year-old male with a history of radiation therapy for thyroid ophthalmopathy was followed up for chronic bilateral vision loss and macular edema refractory to multiple intravitreal treatments for over 19 years. His clinical course included multiple intravitreal injections including triamcinolone acetonide, bevacizumab, pegaptanib, ranibizumab, aflibercept 2 and 8 mg, and dexamethasone implant. At the 17th year of follow-up, spectral-domain optical coherence tomography (OCT) revealed intensely hyperreflective, horizontally layered deposits within intraretinal cystic spaces without posterior shadowing, consistent with the onion ring sign. Fundoscopic examination showed highly refractile, golden-yellow lipid exudates corresponding to these OCT findings. Unlike previously reported cases of age-related macular degeneration and diabetic retinopathy, where these deposits were located primarily beneath or above the retinal pigment epithelium, the deposits in this patient were located within the inner retinal layers. The present case demonstrates that the onion ring sign may develop in long-standing radiation retinopathy, likely reflecting the cumulative effects of chronic vascular injury and persistent macular edema. The recognition of this OCT feature may aid in understanding the natural history, chronicity, and metabolic burden of retinal vascular disorders.