Conditions · Ophthalmology and ENT
Ocular toxoplasmosis (retinochoroiditis) !
Infection of the retina by the parasite Toxoplasma gondii, the commonest cause of posterior uveitis in Colombia; it can scar the macula and recurs.
Updated 2026-11-01
Structures involved
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Why it happens
- Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous
- Retina: the ten layers, rods and cones
What it is
A necrotising retinochoroiditis caused by Toxoplasma gondii, acquired after birth or congenitally. It is the leading infectious cause of posterior uveitis worldwide and typically recurs at the edge of old scars.
Who gets it
Very common in Colombia and Brazil, where the parasite strains seem more aggressive for the eye. In Quindío, Colombia, the annual incidence is about three new episodes per 100,000 people, and population screening in Armenia found retinochoroidal scars in a notable share of the people examined.
Causes
- Toxoplasma gondii, an intracellular protozoan whose definitive host is the cat
- Acquired by eating undercooked meat with cysts or food and water contaminated with oocysts from cat faeces
- Congenital transmission when the mother is first infected during pregnancy
- Reactivation of dormant cysts in old retinal scars
Risk factors
- Drinking untreated water and eating undercooked meat or unwashed produce
- Contact with soil or cat litter
- Living in high-prevalence areas such as the Colombian coffee region
- Weakened immunity (HIV infection, transplant, chemotherapy, older age): more severe and atypical disease
- Pregnancy (risk of congenital infection)
Pathophysiology
Tachyzoites infect and destroy retinal cells, causing a full-thickness focus of necrosis with inflammation spilling into the vitreous. The immune response turns the parasites into tissue cysts that lie dormant at the scar border. Later, cysts rupture and cause new active foci next to the old pigmented scar (satellite lesions). A lesion near the macula or optic disc threatens central vision.
Classification
- Congenital or acquired
- Primary lesion or recurrence next to a scar
- Typical, or atypical (punctate outer retinal, large or multifocal lesions in immunosuppressed people)
- Peripheral or sight-threatening (zone near the macula or optic disc)
Symptoms and signs
- Floaters and blurred vision in one eye
- Mild pain, redness or sensitivity to light when the anterior uvea is involved
- Loss of central vision when the macula is involved
- Inactive scars may be found by chance on fundus examination
Diagnosis
- Clinical
- Mainly clinical by dilated fundus examination: a white focus of retinochoroiditis with overlying vitritis (headlight in the fog appearance), often next to a pigmented scar.
- Tests
- Toxoplasma IgG supports exposure but is common in the population; IgM suggests recent infection. In doubtful or atypical cases, PCR of aqueous or vitreous fluid. HIV testing in atypical or severe disease.
- Imaging
- Retinal photography to document and follow the lesion; optical coherence tomography and angiography for macular involvement; ultrasound when the vitreous is too hazy.
Differential diagnosis
- Cytomegalovirus retinitis (in HIV)
- Acute retinal necrosis (herpes viruses)
- Ocular toxocariasis
- Syphilis and tuberculosis uveitis
- Fungal endophthalmitis and intraocular lymphoma
Goal of treatment
Shorten active inflammation and limit the size of the scar, protect the macula and optic nerve, and reduce recurrences in people at high risk.
Treatment
- Medical
- Antiparasitic treatment for sight-threatening or large lesions, immunosuppressed patients and congenital disease: pyrimethamine with sulfadiazine and folinic acid, or trimethoprim-sulfamethoxazole; clindamycin and azithromycin are alternatives.
- Medical
- Oral glucocorticoids may be added after antiparasitic therapy has started to control vitreous and retinal inflammation; steroids are never given alone.
- Conservative
- Small peripheral lesions in immunocompetent people can heal on their own and may be observed.
- Medical
- Prophylaxis with trimethoprim-sulfamethoxazole is used in selected patients with frequent recurrences.
- Follow-up
- Follow-up fundus examinations until healing, blood counts during antifolate therapy, and screening in pregnancy and in newborns at risk.
Complications
- Macular scar with permanent central vision loss
- Recurrences
- Retinal detachment and epiretinal membrane
- Choroidal neovascularisation
- Secondary glaucoma and cataract
- Optic nerve involvement
Prognosis
Active lesions usually heal in one to two months, leaving a scar. Recurrences are common, especially in the first years. The visual outcome depends on lesion location: peripheral scars are often silent, while macular lesions cause lasting loss of central vision.
Prevention
- Drinking boiled or treated water
- Cooking meat well and washing fruit and vegetables
- Hand washing after handling soil, raw meat or cat litter
- Serological screening in pregnancy and fundus screening in high-prevalence areas
Test yourself
Think of the answer, then tap the question to see it.
What is the classic fundus appearance of active ocular toxoplasmosis?
A white focal retinochoroiditis with overlying vitritis, the headlight in the fog look, often beside an old pigmented scar.
What is the most common cause of infectious posterior uveitis in Colombia?
Ocular toxoplasmosis (Toxoplasma gondii retinochoroiditis).
Which classic drug combination treats sight-threatening ocular toxoplasmosis?
Pyrimethamine plus sulfadiazine with folinic acid; trimethoprim-sulfamethoxazole is a common alternative.
Why should corticosteroids not be given alone in ocular toxoplasmosis?
Without antiparasitic cover they allow the parasite to multiply and the lesion to enlarge.
Which retinitis in a patient with advanced HIV is the main differential, with haemorrhages and little vitritis?
Cytomegalovirus retinitis.
Related conditions
- Toxoplasmosis
- Uveitis
- HIV infection and AIDS
- Cytomegalovirus infection
- Toxocariasis (visceral and ocular larva migrans)
- Retinal detachment
Educational information, not medical advice. For any symptom, see a health professional.
Sources: High frequency of ocular toxoplasmosis in Quindío, Colombia and risk factors related to the infection (Heliyon, 2021) · adapted, CC BY 4.0; About Toxoplasmosis | Toxoplasmosis | CDC (Centers for Disease Control and Prevention, 2024).
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