Birdshot uveitis, also known as birdshot chorioretinopathy, is a rare and chronic form of inflammation that affects the back of the eye. This condition involves the retina, the light-sensitive tissue, and the choroid, the layer of blood vessels that nourishes it. The name is derived from the distinctive pattern of small, cream-colored spots scattered across the retina, resembling pellets from a shotgun. Affecting both eyes, this inflammatory disease requires ongoing management to preserve vision and most commonly develops in Caucasian individuals between 40 and 60.
Identifying the Symptoms
The onset of birdshot uveitis is often gradual, with initial symptoms that can be subtle. Many individuals first notice an increase in floaters, which appear as drifting spots or webs, and blurred or hazy vision, sometimes described as looking through murky water. These early symptoms may have little impact on the ability to see clearly, which can delay a person from seeking medical care.
As the condition progresses, patients may experience difficulty seeing in low light or at night (nyctalopia) and a noticeable decrease in the vibrancy of colors. Sensitivity to bright lights, or photophobia, can also make well-lit environments uncomfortable. Unlike many other forms of uveitis, birdshot is painless, and symptom severity can differ between the eyes.
Causes and Risk Factors
Birdshot uveitis is an autoimmune disorder, a condition where the body’s own immune system incorrectly targets and attacks its healthy tissues. In this case, the immune response is directed at cells within the retina and the underlying choroid. The precise trigger for this autoimmune reaction is not yet known, but research has identified a strong genetic predisposition linked to a specific marker.
This genetic connection is with a human leukocyte antigen known as HLA-A29. Over 95% of individuals diagnosed with birdshot uveitis test positive for the HLA-A29 antigen. Carrying the gene does not mean a person will develop the disease, as it is also found in about 7% of the general Caucasian population. However, its absence makes a diagnosis of birdshot uveitis highly improbable. The condition is not contagious or caused by an infection.
The Diagnostic Process
Confirming a diagnosis involves a multi-step process led by an ophthalmologist. The first step is a dilated eye exam, where special drops widen the pupils for a clear view of the retina and choroid. This allows the physician to look for the characteristic spots, though they may not be present in the early stages.
Specialized imaging tests are used to confirm the extent of inflammation. Fluorescein angiography involves injecting a dye into a vein and using a special camera to reveal leakage from blood vessels in the retina, a sign of active inflammation. Optical coherence tomography (OCT) uses light waves to create detailed cross-sectional images of the retina, which is useful for detecting swelling known as cystoid macular edema.
A blood test to check for the HLA-A29 antigen is a key part of the workup, as a positive result provides significant evidence for the diagnosis. Other tests may be ordered to rule out conditions with similar symptoms, like syphilis or sarcoidosis.
Treatment Approaches
The goals of treating birdshot uveitis are to control inflammation, prevent retinal damage, and preserve long-term vision. The initial approach for acute inflammation involves corticosteroids like prednisone. These drugs can be administered as eye drops, injections, or oral pills to quickly suppress inflammation, but significant side effects make them unsuitable as a permanent solution.
Due to the chronic nature of the disease, long-term management relies on immunomodulatory therapy (IMT). These “steroid-sparing” agents, such as methotrexate and mycophenolate mofetil, control the overactive immune system, reducing the need for corticosteroids. Finding the right medication or combination of drugs can be a process of trial and adjustment.
For cases that are difficult to control, a class of medications known as biologics may be used. Biologics are targeted therapies, such as adalimumab and infliximab, that interfere with specific components of the immune system. They work by blocking a key protein that promotes inflammation.
Long-Term Management and Outlook
Birdshot uveitis is a lifelong condition that necessitates continuous and specialized medical supervision, even when the disease appears to be inactive or in remission. Regular follow-up appointments with an ophthalmologist are necessary to monitor for any signs of returning inflammation or potential complications. This consistent oversight allows for prompt adjustments to treatment, which is fundamental to preserving vision over the long term.
While there is currently no cure, the visual prognosis for patients has improved considerably with modern immunomodulatory treatments. Early diagnosis and consistent management allow many individuals to maintain good functional vision for many years. Part of long-term management involves monitoring for potential complications from the disease or its treatment. These can include:
- Cystoid macular edema (CME), which is swelling in the macula responsible for sharp, central vision.
- Cataracts, a clouding of the eye’s lens that can be accelerated by corticosteroid use.
- Glaucoma, a condition of increased eye pressure that can damage the optic nerve.