Optometry case study: Toxoplasmosis

764

by Evon Chan, Optometrist, Mount Barker, South Australia

History
A 5 year old boy was referred for an eye examination following a pre-school screening.

Examination
• Unaided visions found by pre school screening: RE 6/9
LE 6/38
• Unaided visions found by optometrist: RE 6/6
LE 6/10
• The patient strongly objected to having their right eye covered.
• PGH – no issues during the mother’s pregnancy. The child was born 2 weeks premature.
• POH – nil
• FOH – nil
• PERRLA
• Retinoscopy – mild hyperopia R&L

Digital retinal photography
• RE – normal
• LE

 

 

 

 

Diagnosis
Ocular Toxoplasmosis

Discussion
Causal agent:
Toxoplasma gondii is a protozoan parasite that infects most speciesof warm blooded animals, including humans, and can cause the disease toxoplasmosis.

Life cycle:
The only known definitive hosts for Toxoplasma gondii are domestic cats and their relatives. Animals bred for human consumption and wild game may also become infected with tissue cysts after ingestion of cysts in the environment. Humans can be infected by a number of routes:
• eating undercooked meat of animals harboring tissue cysts
• consuming food or water contaminated with cat feces or by contaminated environmental samples (such as fecalcontaminated soil or changing the litter box of a pet cat)
• blood transfusion or organ transplantation
• transplacentally from mother to fetus.

Clinical features:
Acquired infection with Toxoplasma in immunocompetent persons is generally an asymptomatic infection. However, 10% to 20% of patients with acute infection may develop a flu-like illness. The clinical course is usually benign and self-limited; symptoms usually resolve within a few weeks to months. In rare cases Ocular Toxoplasmosis can occur.

Ocular Toxoplasma infection, an important cause of retinochoroiditis, can be the result of congenital infection, or infection after birth. In congenital infection, patients are often asymptomatic until the second or third decade of life, when lesions develop in the eye. The Toxoplasma gondii parasite, can lie dormant in the retina for many years. However, if the parasite becomes active again it can start a new infection.

Symptoms are typically photophobia and an increase in floaters.

Slit lamp examination may reveal a mild to moderate anterior chamber reaction along with a yellow focus of retinochoroiditis.

Treatment
Systemic Toxoplasmosis:
Treatment is not needed for a healthy person who is not pregnant. Symptoms will usually go away within a few weeks. Treatment may be recommended for pregnant women, persons who have weakened immune systems, or persons with ocular disease or severe illness.

Ocular Toxoplasmosis:
Treatment may or may not be required depending on the proximity of an active lesion to the macula or optic nerve head. Classical treatment consists of a combination of antibiotics and antiprotozoan drugs. If the inflammationis severe systemic steroids may be required.

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