The is a retinal infiltrate. It consists of inflammatory cells, dead retinal tissue, and perhaps micro-organisms. Its indistinct margins and overlying vitreous haze distinguish it from other yellow-white things in the retina.
This patient has retinal toxoplasmosis. In immunocompromised hosts, such as this patient with HIV disease, the toxoplasmosis is usually acquired, and no old scars are seen. In immunocompentent hosts, this condition usually represents satellite reactivation of a congenital lesion, evident as an adjacent healed .