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Ophthalmology – Birdshot Chorioretinopathy
Birdshot chorioretinopathy is a rare, chronic, bilateral form of posterior uveitis characterized by distinctive cream-colored lesions at the level of the choroid. These lesions radiate outward from the optic nerve, resembling the scattered pattern of birdshot from a shotgun. The disease is strongly associated with the HLA-A29 allele, with over 90% of affected individuals testing positive, making it one of the strongest HLA-disease associations in medicine.
This condition primarily affects middle-aged adults, with an average onset around 50 years of age, and is more commonly seen in individuals of Caucasian descent. Both males and females are affected equally. Although the exact cause remains unclear, the disease is believed to be autoimmune in nature, likely involving a type IV hypersensitivity reaction targeting retinal or choroidal antigens.
Patients typically present with gradual, painless, bilateral visual decline. Common symptoms include floaters, nyctalopia (night vision difficulty), photopsias, photophobia, peripheral visual field loss, and impaired color vision. Despite these symptoms, the eyes may appear relatively quiet externally, with minimal anterior segment inflammation. On examination, mild to moderate vitreous inflammation is often present. The hallmark finding is the presence of multiple cream-colored choroidal lesions with indistinct borders. Cystoid macular edema (CME) is a frequent complication and a major cause of decreased visual acuity. Retinal vasculitis and optic disc edema may also be observed.
Diagnosis is largely clinical but supported by ancillary testing. HLA-A29 testing is highly sensitive and specific. Imaging studies are essential: fluorescein angiography shows early hypofluorescence and late leakage, while indocyanine green angiography often reveals more lesions than are clinically visible. Optical coherence tomography is useful for detecting macular edema. Electroretinography frequently shows reduced photopic and scotopic responses, and visual field testing often demonstrates peripheral constriction. It is important to exclude other causes of posterior uveitis, such as infections (e.g., syphilis, tuberculosis, Lyme disease), sarcoidosis, or intraocular lymphoma.
Management typically involves long-term immunosuppression. Corticosteroids, either systemic or local, are effective for initial control of inflammation, but due to the chronic nature of the disease and the side effects of prolonged steroid use, steroid-sparing immunomodulatory agents are often introduced early. These include medications such as cyclosporine, methotrexate, mycophenolate mofetil, and azathioprine. In refractory cases, biologic agents such as anti–tumor necrosis factor (TNF) therapies or intravenous immunoglobulin may be considered. Local steroid injections may also be used for severe inflammation or macular edema.
The disease course is typically chronic and progressive, with periods of exacerbation and remission. Close, long-term follow-up is essential, including regular monitoring with imaging and functional tests. Prognosis is guarded over time, as visual function may decline even when visual acuity appears relatively preserved. Complications such as cystoid macular edema, epiretinal membrane formation, glaucoma (often secondary to steroid use), choroidal neovascularization, and, rarely, optic nerve atrophy can contribute to vision loss.
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