Introduction:

Birdshot retinochoroidopathy, also called vitiliginous chorioretinitis, is a rare bilateral posterior uveitis affecting usually healthy adults between the third to sixth decades of life with a female preponderance. An autoimmune pathogenesis has been suggested with reactivity to the retinal S antigen. There is a strong association with HLA-A29 (>90% of cases). HLA-B44 is also positive in many cases.

Clinical Features:

Decreased vision, photopsias, floaters, nyctalopia, and decreased color vision are frequent symptoms. There is minimal to no anterior uveitis with mild vitritis. Multifocal depigmented cream-colored retinal pigment epithelium lesions less than one disc diameter in size are scattered throughout the fundus, although these may be absent or very subtle in the early stages of the disease (Fig. 17.2.1). Retinal phlebitis, narrowing and sheathing of retinal vasculature, disc edema, optic atrophy, cystoid macular edema, choroidal neovascularization and epiretinal membrane may also develop.

OCT Features:

Lines scan of the macula may show the typical features of birdshot: epiretinal membrane formation and macular edema (Fig. 17.2.2). Subretinal fluid may be seen in severe cases of macular edema. In chronic cases, the macula is diffusely thin and disruption of the IS–OS segment/ellipsoid layer with disorganization of the inner retinal layers and retinal pigment epithelium atrophy may be seen (Fig. 17.2.3). Extramacular and enhanced depth OCT images provide greater information than macular scans, because the choroidal lesions themselves can be scanned. Focal and generalized loss of the IS–OS junction/ellipsoid layer, loss of retinal architecture and outer retinal hyper-reflective foci overlying the lesions is typical. Generalized thinning of the choroid and outer retina, and hyporeflective suprachoroidal space are other features.

Ancillary Testing:

Diagnosis is based on clinical features. On fluorescein angiography, birdshot lesions may block dye in the early phases, and stain in the late phases. All lesions seen on clinical examination may not be evident on FA. There may be retinal vascular leakage, perifoveal capillary leakage, disc edema, staining and late cystoid macular edema. Occasionally, choroidal neovascularization may be seen at the site of old lesions. Indocyanine green angiography reveals early hypofluorescent spots and possible diffuse late leakage. Many more spots may be seen on indocyanine green angiography than on FA further consolidating the theory that this is primarily a choroidal disease.

Electroretinogram shows depressed rod and cone function with a decreased b-wave amplitude and increased latency of the b-wave compared to the a-wave which is relatively preserved. The b-wave may eventually be extinguished in severe cases. The 30 Hz flicker response is delayed with increased implicit times.

HLA testing (HLA-A29) is positive in 80–96% of patients.

Treatment:

The mainstay of treatment is periocular and systemic steroids. Steroid sparing treatments used include cyclosporine, azathioprine, methotrexate, infliximab, immunoglobulins, and mycophenolate mofetil. Targeted treatments are being studied.