Toxoplasmosis in the retina. Ophthalmoscope view of the retina of the eye in a case of toxoplasmosis, a disease 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 (large yellow lesion) which may affect visual acuity. This is a case of inactive toxoplasmosis. The optic disc (lower left) is where the blood vessels are converging, and is affected here by the toxoplasmosis lesion.