Chorioretinitis is an inflammatory condition affecting the posterior segment of the eye. This inflammation involves both the choroid, a vascular layer, and the retina, the light-sensitive tissue. When these two layers become inflamed, the condition can severely interfere with the eye’s ability to process visual information. Prompt diagnosis and intervention are necessary because inflammation in this delicate area carries the risk of permanent vision impairment.
The Anatomy of Chorioretinitis
The choroid is a layer rich in blood vessels situated between the sclera, the outer layer of the eye, and the retina. Its primary function is to supply oxygen and nutrients to the outer layers of the retina. The retina is a thin, multi-layered sheet of nerve tissue that captures light and converts it into electrical signals sent to the brain.
Inflammation in the choroid hinders its ability to sustain the retina, leading to tissue damage. Chorioretinitis refers to the inflammation’s spread from the choroid into the adjacent retinal tissue. This combined inflammation can quickly compromise retinal health and function, leading to scarring and irreversible destruction of the photoreceptor cells needed for sight.
Infectious and Non-Infectious Causes
The inflammation seen in chorioretinitis can arise from a wide range of sources, which are broadly categorized as infectious or non-infectious. Identifying the specific cause is necessary because treatment is targeted directly at the underlying trigger. Infectious agents are responsible for the majority of cases globally.
The parasite Toxoplasma gondii is the most frequently identified infectious cause of chorioretinitis worldwide, resulting in ocular toxoplasmosis. Infection typically occurs by ingesting tissue cysts found in raw or undercooked meat or by consuming oocysts from contaminated soil or cat feces. In the United States, a significant portion of cases are congenital, transmitted from the mother to the fetus during pregnancy. Active toxoplasmosis causes a necrotizing chorioretinitis that appears as a fluffy, white lesion often described as a “headlight in a fog” due to overlying vitreous inflammation.
Viral and Bacterial Causes
Viral infections represent a significant group of causes, particularly in individuals with compromised immune systems. Cytomegalovirus (CMV) is a common culprit, especially in patients with advanced human immunodeficiency virus (HIV) infection or those undergoing immunosuppressive therapy. Other viruses that can trigger this condition include Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV).
Bacteria like Mycobacterium tuberculosis and Treponema pallidum, which causes syphilis, are also known to cause chorioretinitis. Fungal organisms, such as those responsible for histoplasmosis, can lead to lesions in the choroid that may eventually involve the retina.
In cases where no infectious agent is found, the chorioretinitis is considered non-infectious and is often linked to systemic autoimmune conditions. Disorders like sarcoidosis, which causes inflammatory cell collections, or Behçet’s disease, a form of vasculitis, can lead to inflammation in the posterior segment of the eye. These non-infectious causes often require a different diagnostic and management approach focused on modulating the immune system.
Identifying Symptoms and Diagnosis
The symptoms of chorioretinitis depend heavily on the size and location of the inflammation. Patients commonly report visual disturbances such as a sudden increase in floaters (small specks moving across the field of vision). Blurred or hazy vision is also frequently reported, particularly if the inflammation is near the macula, the center of the retina responsible for sharp central vision.
Other possible symptoms include scotomas (fixed blind spots) and photophobia (increased sensitivity to light). While inflammation in the back of the eye is often painless, pain or redness may occur if the inflammation spreads to the anterior parts of the eye. Diagnosis begins with a comprehensive, dilated eye examination, using an ophthalmoscope to directly visualize the back of the eye and the characteristic inflammatory lesions.
Specialized imaging techniques provide further detail about the extent of the damage. Fluorescein angiography (FFA) involves injecting a dye to highlight blood flow issues and leakage. Optical Coherence Tomography (OCT) is a non-invasive scan that provides cross-sectional images of the retina, allowing for precise measurement of thickness and swelling. Blood tests and polymerase chain reaction (PCR) tests are often ordered to identify the specific pathogen, such as Toxoplasma antibodies or viral DNA, which guides the choice of therapy.
Treatment Strategies and Long-Term Outlook
Treatment for chorioretinitis is always tailored to the specific underlying cause identified during the diagnostic workup. For infectious etiologies, the primary goal is to eliminate the pathogen using targeted antimicrobial therapy. Ocular toxoplasmosis, for example, is typically treated with a combination of anti-parasitic medications, such as pyrimethamine and sulfadiazine, often administered alongside folinic acid to mitigate potential side effects.
Viral infections, such as those caused by CMV, are managed with specific antiviral drugs like ganciclovir or valganciclovir. In many cases, systemic or locally injected corticosteroids are also used in conjunction with antimicrobials to quickly reduce the damaging inflammation and minimize scarring. Non-infectious or autoimmune-related chorioretinitis is managed primarily with corticosteroids and, in certain chronic cases, with steroid-sparing immunosuppressive agents.
The long-term outlook for a person with chorioretinitis is highly dependent on the speed of diagnosis and the location of the inflammation. Early treatment significantly improves the chances of preserving vision and preventing permanent structural damage. However, inflammation that affects the central macula or optic nerve carries a higher risk of lasting vision loss. Even after successful treatment, the inflamed area often heals with a chorioretinal scar, and some infectious causes, like toxoplasmosis, can reactivate and cause recurrent episodes of inflammation.