My niece lost one of her eyes to infection many years ago. After extended treatment with eye drops, she underwent an operation to get a glass eye. Today she's doing well with her one good eye. Her doctor told the family that sight-threatening pathogens are more common than we think, and children can acquire them from normal play activities. Many infections target only the front surface of the eye or eyelid, and are not serious. But when infection reaches the uvea, which consists of the iris, choroid, and ciliary body, then vision is at risk.
Toxoplasma gondii is a protozooan parasite responsible for the majority of infections of the uvea worldwide. According to the Centers for Disease Control, more than 60 million residents of the United States are infected with this parasite, but very few have symptoms. The disease can be serious for pregnant women and for anyone with a weakened immune system. Babies born to infected mothers are at high risk of congenital toxoplasmosis. The parasite can cross the placenta to infect the fetus. Sources of infection for adults include contaminated food or water, waste from infected cats, and blood transfusion or organ transplant from an infected person. Toxoplasmosis is the third leading cause of death attributed to foodborne illness in the U.S.
Ocular toxoplasmosis is also called toxoplasmic retinochoroiditis. Active lesions, where the parasites multiply, form primarily on the retina. These can be seen on a standard eye exam. Inflammation may affect the choroid and sclera. These are the layers of the eye outside the retina: the choroid contains blood vessels and connective tissue, while the sclera is the outermost white of the eye. Symptoms include:
1.Blurred vision
2.Floaters
3.Pain
4.Red eye
5.Light sensitivity (photophobia)
6.Distorted vision (metamorphopsia)
Complications seen mostly in children include cataract, glaucoma, optic nerve atrophy, retinal detachment, and growth of abnormal blood vessels in the choroid.
The treatment includes antimicrobial drugs such as pyrimethamine, sulfadiazine, spiramycin, clindamycin, and themethoprim-sulfamethoxazol. Recurrences are unfortunately common, possibly caused by the rupture of a dormant cyst on the retina. Injections of antimicrobial drugs into the eye may be indicated for some patients.
There are 22 clinical trials for toxoplasmosis treatment currently listed at http://clinicaltrials.gov.
References:
Commodaro AG et al, “Ocular toxoplasmosis – an update and review of the literature”, Mem Inst Oswaldo Cruz, Rio de Janeiro, March 2009; 104(2): 345-350.
Centers for Disease Control information:
http://www.cdc.gov/toxoplasmosis/
Ocular toxoplasmosis information with photos:
http://emedicine.medscape.com/article/1204441-overview
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.