Toxoplasmosis of retina. Ophthalmoscope view of the retina of the eye of a patient suffering from toxoplasmosis. Toxoplasmosis is caused by the single-celled protozoan Toxoplasma gondii. It is contracted most commonly from undercooked meat and infected dogs, cats and birds. The infection causes scarring of the retina (yellow lesions seen here) which may affect visual acuity. The yellow lesions are areas of chorioretinal tissue atrophy. In most cases, the body's immune system protects against the organism. However, in AIDS sufferers with an immunodeficiency disorder, toxoplasmosis can also damage the heart, lungs and brain. It may be treated with antimalarial & sulphonamide drugs.