Ocular toxoplasmosis is an infection in the eye caused by the parasite, Toxoplasm a gondii. Toxoplasmosis is the most common cause of eye inflammation in the world. Toxoplamosis can be acquired or present at birth (congenital), having crossed the placenta from a newly infected mother to her fetus. Most humans acquire toxoplasmosis by eating raw or undercooked meat, vegetables or milk products, or by coming into contact with infected cat litterbox or sandboxes. In humans, the infection usually causes no symptoms, and resolves without treatment in a few months. In individuals with compromised immune systems, Toxoplasm a gondii can reactivate to cause disease.  

Reactivation of a congenital infection was traditionally thought to be the most common cause of ocular toxoplasmosis, but an acquired infection is now considered to be more common. A toxoplasmosis infection that affects the eye usually attacks the retina and initially resolves without symptoms. However, the inactive parasite may later reactivate causing eye pain, blurred vision, and possibly permanent damage, including blindness. Although most cases of toxoplasmosis resolve on their own, for some, inflammation can be treated with antibiotics and steroids.

In individuals with a normally functioning immune system and mild symptoms that do not threaten the function of the eye, treatment may not be needed and symptoms may resolve within 4-8 weeks. For cases in which there is a potential for vision loss, treatment may involve the use of anti-parasitic medications, steroids, and antibiotics. Typically, the anti-parasitic medication pyrimethamine is utilized in combination with the antibiotic sulfadiazine and corticosteroids. Other medications that have been used in individuals with ocular toxoplasmosis include the antibiotics clindamycin, azithromycin, and trimethoprim-sulfamethoxazole and the steroid dexamethasone.

The long-term outlook (prognosis) for ocular toxoplasmosis is dependent on what part of the eye is affected. Symptoms during an infection resulting in abnormal vision (blurriness, loss) are usually associated with involvement of the macula (the part of the eye needed for sharp, central vision) or the optic nerve. Vision loss may become permanent if a scar forms around the macula or if damage to the optic nerve occurs (optic nerve atrophy). If a scar forms around the optic disk (point of entry of the optic nerve in the eye), vision loss may be severe.