Birdshot chorioretinitis

Description

Birdshot chorioretinitis is an uncommon cause of chronic, bilateral, posterior uveitis that typically occurs in middle-aged women. It is characterized by multiple patches of depigmentation of the choroid and retinal pigment epithelium. Its alternative name, vitiliginous chorioretinitis, reflects its resemblance to the skin condition, vitiligo. Although the pathogenesis of birdshot chorioretinitis is unknown, immunological evidence suggests a role for genetic predisposition and retinal autoimmunity. The great majority of patients express the h4LA-A29 antigen, and around half demonstrate immunological sensitivity to purified retinal S-antigen. Well described responses to immunosuppressive therapy have been consistent with these findings.

Symptoms

Patients usually present with floaters, flashing lights (photopsias) or blurred vision. Reduced rod or cone function may cause impaired night or color vision. Central vision is rarely affected.

Signs

Eye involvement is usually symmetrical. Fundoscopy reveals bilateral, multiple, pale-yellow to orange patches with indistinct margins radiating from the optic disc. The macula is often involved. Cystoid macular edema or disc swelling may be visible. There may be narrowing of retinal vessels and mild optic atrophy. A variable number of small, well defined masses, thought to be inflammatory cells, are present in the posterior vitreous. After several weeks to months, most patches evolve into atrophic, pale scars. Some lesions become hyperpigmented.

Prevalence

Rare; usually occurs in middle-aged  women

Significance

May lead to significant bilateral visual loss.

Differential diagnosis

Pars planitis; intraocular lymphoma; sarcoidosis; candida infection presumed ocular histoplasmosis syndrome.

See also

Posterior uveitis.

Management

Blood tests HLA typing is useful in making a diagnosis of birdshot chorioretinitis. As most patients are HLA-A29 positive, a negative result may prompt consideration of an alternative diagnosis.

Ocular tests Findings on fluorescein angiography are often normal in the early stages of disease. Established lesions may show late hyperfluorescence in the macular region, increased retinal circulation time, and late intraretinal and optic disc leakage.

Medications Systemic steroids or other immunosuppressive agents, such as cyclosporin, are often administered. Most patients respond poorly.

Prognosis Birdshot chorioretinitis is variable in its severity, disease progression and response to treatment. It is usually a chronic, slowly progressive disease with occasional exacerbations and remissions. Although most cases eventually stabilize with reasonable central
vision in at least one eye, central vision may be affected by macular edema, serous macular detachment or optic atrophy. Rarely, new vessel proliferation from the optic disc and retina may cause vitreous hemorrhage.