Toxoplasmosis is a zoonotic infection caused by the protozoan parasite Toxoplasma gondii. It is the most common cause of posterior uveitis and focal retinitis. The disease typically affects immunocompetent individuals.
In recurrent cases, there is a characteristic focus of active chorioretinitis with overlying vitritis adjacent to a pigmented chorioretinal scar (Fig. 18.1.1). Associated retinal vasculitis may be present. The disease is almost always unilateral. Primary infection may present with a similar appearance in the absence of a pigmented scar (Fig. 18.1.2). Multifocality and bilaterality are rare except in immunocompromised individuals. In elderly patients, a severe form of toxoplasmosis that is relentlessly progressive, resembling acute retinal necrosis, can occur.