Birdshot Chorioretinopathy (Birdshot Uveitis) Clinical Presentation

Updated: May 29, 2019
  • Author: Hemang K Pandya, MD; Chief Editor: C Stephen Foster, MD, FACS, FACR, FAAO, FARVO  more...
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Presentation

History

The course of birdshot chorioretinopathy, like other autoimmune diseases, is characterized by exacerbations and remissions. The principle-presenting symptom is gradual, painless vision loss, frequently complicating of floaters that may initially involve one eye but later affect the fellow eye.

A study was conducted on NEI population with birdshot chorioretinopathy (n=59). This study showed that the most common complaint of NEI population was decreased vision (68%), floaters (29%), nyctalopia (25%), dyschromatopsia (20%), glare (19%), and photopsia (17%).

Other less frequent symptoms are as follows:

  • Decreased vision - 68%
  • Floaters - 29%
  • Nyctalopia - 15%
  • Dyschromatopsia - 12%
  • Glare - 19%
  • Photopsia - 17%
  • Fluctuating vision - 7%
  • Pain - 7%
  • Decreases depth of perception - 5%
  • Shimmering vision - 3%
  • Metamorphopsia - 3%
  • Decreased peripheral vision - 3%
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Physical

Decreased visual acuity in the initial stages of birdshot chorioretinopathy is often mild; in many cases, visual acuity is not worse than 20/40 and rarely below 20/80. Visual dysfunction, however, can be pronounced and yet go undetected if the patient is not assessed with electroretinography and SITA-SWAP visual field testing, which typically show obvious abnormalities early in the disease course. Significant impairment most often is related to the presence of macular edema, but macular involvement by an active lesion, atrophic scar, severe vitritis, and choroidal neovascular membrane are other potential causes of more significant visual acuity loss.

Slit lamp biomicroscopy usually reveals a quiet eye, with anterior chamber cells only in instances in which significant vitreal reaction is present, and, rarely, one may see nongranulomatous keratic precipitates on the corneal endothelium and iridocapsular synechiae.

The major signs are seen in the posterior segment of the eye. Vitritis is typical, but neither "snowballs" nor a pars plana exudate is present.

Birdshot chorioretinopathy lesions

The classic birdshot chorioretinopathy lesions are small, from one fourth to one and one half times the size of a disk diameter, although they may appear larger if they become confluent.

Two types of lesions are described; the first is not sharply demarcated and is slightly oval. These spots are pale yellow or cream in color and are seen most easily on indirect ophthalmoscopy; they are very subtle and may escape detection by slit lamp examination with 78 diopter (D) or 90 D lens. These lesions represent the earliest form of the lesions. It is critical to emphasize the utility of indocyanine green angiography in assessing any patient who might have birdshot chorioretinopathy, since typical choroidal lesions are seen with this imaging modality much earlier than with fluorescein angiography.

The second type of lesion is an atrophic one, more sharply demarcated, round, and "punched out." These atrophic lesions can be seen easily either by indirect ophthalmoscopy or by direct 78 D or 90 D examination.

Several case reports hypothesize that the initial subtle lesions evolve into the atrophic lesions, although most reports describe birdshot chorioretinopathy lesions as having a stable appearance over time. Patients may have both kinds of lesions present simultaneously. Characteristically, neither is associated with increased pigmentation, and this can help distinguish these lesions from similar-appearing entities, such as presumed ocular histoplasmosis syndrome.

The birdshot chorioretinopathy lesions usually are scattered around the posterior pole and can extend to the equator. In most cases, they do not extend more peripherally. They usually are flat, although, in active lesions, they may be associated with a slight elevation.

The appearance of the birdshot chorioretinopathy lesions may present well after the initial onset of uveitis. In some patients, the disease first presents as a vitritis with vasculitis, most obvious on fluorescein angiography, with no characteristic fundus lesions. It may take up to 8 years for the characteristic fundus lesions to appear on ophthalmoscopy and, hence, occasionally can result in a delayed diagnosis.

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Causes

The cause of birdshot chorioretinopathy is unknown.

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Complications

The following are potential complications:

  • Chronic cystoid macular edema – 50%; the most common cause of reduced central visual acuity

  • Epiretinal membrane - 10%

  • Macular pucker

  • Choroidal neovascularization

  • Peripapillary subretinal neovascularization - 6%

  • Retinal neovascularization located on the optic disc

  • Peripheral retinal neovascularization with capillary nonperfusion

  • Optic nerve atrophy

  • Other complications, such as cataract, glaucoma, and rhegmatogenous retinal detachment

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