Toxoplasma chorioretinitis, more simply known as ocular toxoplasmosis, is possibly the most common cause of infections in the back of the eye (posterior segment) worldwide. The causitive agent is Toxoplasma gondii, and in the United States, most cases are acquired congenitally. The most common symptom is decreased visual acuity in one eye. The diagnosis is made by examination of the eye, using ophthalmoscopy. Sometimes serologic testing is used to rule out the disease, but due to high rates of false positives, serologies are not diagnostic of toxoplasmic retinitis. If vision is not compromised, treatment may not be necessary. When vision is affected or threatened, treatment consists of pyrimethamine, sulfadiazine, and folinic acid for 4–6 weeks. Prednisone is sometimes used to decrease inflammation. Signs and symptoms
A unilateral decrease in visual acuity is the most common symptom of toxoplasmic retinitis. Under ophthalmic examination, toxoplasmic chorioretinitis classically appears as a focal, white retinitis with overlying moderate inflammation of the vitreous humour. A unifocal area of acute-onset inflammation adjacent to an old chorioretinal scar is virtually pathognomonic for toxoplasmic chorioretinitis. Focal condensation of vitreous and inflammatory cells may be seen overlying the pale yellow or gray-white raised lesion in the posterior pole. Pathophysiology
Toxoplasma gondii is an intracellular parasite that causes a necrotizing chorioretinitis. Congenital disease
Congenital disease occurs due to the acquisition of the organism by a pregnant woman exposed to tissue cysts or oocytes in uncooked meat or substances contaminated with cat feces. Spontaneous abortion may result if the disease is acquired during the first trimester.
Sight-threatening lesions are treated for 4–6 weeks with triple therapy consisting of pyrimethamine, sulfadiazine, and folinic acid. During treatment with pyrimethamine, leukocyte and platelet counts should be monitored weekly. Folinic acid protects against the decrease in platelets and white blood cells induced by pyrimethamine. Prednisone may be used for 3–6 weeks to reduce macular or optic nerve inflammation and can be started on day 3 of antibiotic therapy. Corticosteroids should not be used without concurrent antibiotic treatment or in immunocompromised patients due to the risk of exacerbation of the disease. Currently, there is no published evidence from randomized controlled trials demonstrating that corticosteroids would be an effective adjunct for treating ocular toxoplasmosis.Trimethoprim-Sulfamethoxazole has been shown to be equivalent to triple therapy in the treatment of ocular toxoplasmosis and may be better tolerated. Clindamycin and azithromycin  can also be considered as alternative therapies. Spiramycin may be used safely without undue risk of teratogenicity and may reduce the rate of transmission to the fetus. AIDS patients require chronic maintenance treatment. See also
Toxoplasmosis

References
External links
Acquired Ocular Toxoplasmosis (Univ of Iowa
Hafidi, Zouheir; Daoudi, Rajae (January 2014). "Chorioretinal Toxoplasmosis". New England Journal of Medicine. 370 (4): 361. doi:10.1056/NEJMicm1306819.