Chorioretinitis 

Chorioretinitis (CR) is an inflammatory process that involves the uveal tract of the eye.

Inflammation is usually caused by congenital viral, bacterial, or protozoal infections in neonates. Congenital toxoplasma and cytomegalovirus (CMV) infection are the most common etiologies in this age group. Fungal infections are commonly identified, and emergent pathogens such as West Nile virus and lymphocytic choriomeningitis virus (LCMV) have been described.^{[1, 2]} In rare instances, chorioretinitis is part of a systemic noninfectious process.

Chorioretinitis associated with congenital viral infections like CMV tends to be stable or improve in infancy, whereas chorioretinitis associated with asymptomatic congenital toxoplasmosis (CTP) progresses for years after birth and is more likely to be clinically significant at an older age.

Although CMV is the most common congenital infection in the developed world, affecting approximately 1% of all infants born in the United States, only 10% of all infants born in the United States with congenital CMV infection have symptomatic disease at birth, including chorioretinitis.^[3]

Congenital disseminated infections such as CMV and toxoplasmosis may also manifest with extraocular findings such as intrauterine growth retardation, microcephaly, microphthalmia, cataract, uveitis, hearing defect, osteomyelitis, hepatosplenomegaly, lymphadenopathy, dermal erythropoiesis, carditis, and congenital heart disease.

Beyond the neonatal period, chorioretinitis can be diagnosed in diverse clinical conditions and can reflect newly acquired diseases or reactivation. CTP is the most common cause of infectious chorioretinitis in immunocompetent children.^[4] Chorioretinitis can also result from a dissemination of parasitic infections like Toxocara or Baylisascaris (the raccoon roundworm) in immunocompetent patients.^[5] In severely immunodeficient patients, including those with acquired immunodeficiency syndrome (AIDS), chorioretinitis may be associated with Epstein-Barr virus (EBV), CMV, varicella-zoster virus, various fungi (eg, Candida, Aspergillus, Fusarium, dimorphic fungi), and Toxoplasma.^[6] See the image below.

In addition, with increasing air travel and globalization, several emerging infectious diseases have been recognized as causing ocular disease, including retinitis, chorioretinitis, retinal vasculitis, and optic nerve involvement. These include rickettsiosis, Rift Valley fever, dengue fever, and Chikungunya virus.^[7]

Chorioretinitis affects the uveal tract, which consists of the iris, ciliary body, and choroid. Inflammatory conditions are generally classified according to the predominant compartment of involvement (eg, anterior and posterior uveitis). Inflammation of the posterior uveal tract of the eye is generally termed choroiditis; because the retina is invariably involved, the terms chorioretinitis or retinochoroiditis are generally used.^[8]

The extent of ocular involvement depends on the organism. Bilateral focal or extensive exudative chorioretinitis or panuveitis may be seen in patients with Toxoplasma gondii infection. A single large choroidal lesion with extensive inflammation or endophthalmitis is usually observed in patients with Toxocara canis, whereas interstitial keratitis or iritis is most common in patients with Treponema pallidum. Strabismus and optic atrophy may accompany chorioretinitis caused by CMV. The central retinal lesions of CMV cannot be clinically distinguished from those of toxoplasmosis. However, unlike congenital toxoplasma infection, the retinitis caused by CMV does not progress.^{[8, 9]}

Vessel trauma caused by other organisms, such as Toxocara or Baylisascaris larvae, may be associated with severe inflammatory responses.

Frequency

United States

Chorioretinitis due to CTP occurs much less frequently in the United States than in Europe. Rates of seroprevalence vary and depend on the population studied. An estimated 400-4,000 cases of CTP occur in the United States each year.^[10] Rates of seroprevalence are much higher in certain European countries (eg, France, Denmark, Germany) where active surveillance systems are in place to detect symptomatic and asymptomatic cases.^{[11, 12]} The risk of retinochoroiditis rises from 10% in infancy to approximately one third by age 12 years in children whose infection was identified by screening. By school age, 20% of infected children with CTP have one or more retinochoroidal lesion.^[13] More than 90% of children have normal vision in their best eye; severe bilateral impairment is rare.

One of the most commonly acquired childhood eyesight impairments in the United States is due to T canis, probably because of the high prevalence of young pet dogs. The incidence is higher in people living in the south-central and southeastern parts of the country. Annually, more than 700 people infected with Toxocara experience permanent partial loss of vision.^[14]

Mortality/Morbidity

If left untreated or if the condition does not respond to treatment, severe chorioretinitis can result in partial or total loss of vision in the affected eye. Morbidity is due to concurrent damage to major organ systems, especially damage to the brain (eg, developmental delays, seizures). Mortality due to chorioretinitis depends on the nature and progression of the underlying illness.

Age

Chorioretinitis due to congenital infections or occasionally other causes is usually evident at birth; progression and prognosis depends on the etiology. Acquired chorioretinitis occurs at any age, depending on the underlying illness.