A toxoplasmosis infection can sometimes spread to the eyes (ocular toxoplasmosis).
The Toxoplasma gondii (T. gondii) parasite, which causes toxoplasmosis, can lie dormant (inactive) in the retina for many years. But if the parasite becomes active again, it can start a new infection.
Ocular toxoplasmosis causes ocular lesions, which are wounds in the eyes caused by inflammation and scarring. These can appear in the:
- retina – the light-sensitive layer of tissue at the back of the eye
- choroid – the layer behind the retina that contains major blood vessels
This damage to the eyes is called retinochoroiditis and can cause eye problems, such as:
- a partial loss of eyesight in one eye
- squint – where one eye looks in a slightly different direction to the other one
- clouding of the eye's lens (cataracts)
- eye shrinking (microphthalmia)
- loss of cells and tissue from the optic nerve, which connects the eye to the brain, resulting in poor vision (optic atrophy)
Antibiotics and steroids are often used to treat the lesions. The scarring caused by toxoplasmosis will not clear up, but treatment may prevent it from getting worse.
If the infection keeps returning, antibiotics may be prescribed on a long-term basis. While this may help prevent the infection recurring, the long-term side effects of these medications are not yet known.
In most cases, babies born with congenital toxoplasmosis develop normally after treatment with antibiotics.
However, in up to 4% of cases, serious complications can develop within the first years of life. These include:
- permanent visual impairment (partial or, very rarely, complete sight loss)
- permanent brain damage
Retinochoroiditis is a common complication of congenital toxoplasmosis.
One study found that 18% of children with congenital toxoplasmosis had at least one ocular lesion as a result of retinochoroiditis. Of these, 42% developed a second ocular lesion later in life.
Cases of ocular toxoplasmosis can also occur years after infection. One study found the average age at which it appeared was nine years old.
It's also possible for someone to develop complications in their 20s or 30s. These may include:
Further research is needed to follow-up cases of congenital toxoplasmosis. Regular eye tests may help detect any abnormalities as they develop, and treatment with antibiotics can limit damage toxoplasmosis causes. However, at present it's not possible to reverse damage already done.