eMedicine Specialties > Ophthalmology > Retina

Retinopathy, Birdshot

Author: C Michael Samson, MD, Associate Professor, Department of Ophthalmology, New York Medical College; Consulting Staff, Co-director of Uveitis Service, Faculty in Residency Training Program, Director of Uveitis Fellowship Training Program, Department of Ophthalmology, New York Eye and Ear Infirmary; Private Practice, Vitreous Retina Macula Consultants of New York
Coauthor(s): Amro Mohamed Mohamoud Ali, MB, ChB, Consulting Staff, New York Eye and Ear Infirmary; C Stephen Foster, MD, FACS, FACR, FAAO, Clinical Professor of Ophthalmology, Harvard Medical School; Consulting Staff, Department of Ophthalmology, Massachusetts Eye and Ear Infirmary; Founder and President, Ocular Immunology and Uveitis Foundation, Massachusetts Eye Research and Surgery Institution
Contributor Information and Disclosures

Updated: Sep 25, 2008

Introduction

Background

Birdshot retinochoroidopathy (BSRC) is an uncommon chronic posterior uveitis characterized by vitritis and multiple ovoid spots, which are orange to cream in color and hypopigmented. These spots are mainly distributed in the posterior pole and in the mid periphery of the retina. The classic presentation is described to "resemble the pattern seen with birdshot in the scatter from a shotgun."
 
Birdshot retinochoroidopathy was first described by Franceschetti and Bable in 1949. In 1980, Ryan and Maumenee coined the term birdshot.¹ Gass described birdshot retinochoroidopathy as vitiliginous choroiditis because of the similarities of the fundus lesion to cutaneous vitiligo.  

Birdshot retinochoroidopathy may indeed represent a clinical disease that has only recently come into existence, and one may wonder what factors from recent times have allowed it to emerge, such as a new strain of virus, an environmental factor, or some yet unrecognized participant in the development of this disease.

Pathophysiology

The cause for birdshot retinochoroidopathy is unknown. A strong link to the presence of the human leukocyte antigen A29 (HLA-A29) molecule exists, suggesting that the disease may result from an inherited immune dysregulation. Multiple case series report 80-93.1% HLA-A29 positivity for patients with birdshot retinochoroidopathy, with a relative risk ratio from 50 to 224. This is the strongest HLA association with any known disease.

LeHoang and coauthors reported a series of European patients in which all patients who were HLA-A29 positive with birdshot retinochoroidopathy expressed the HLA-A29 type 2 subtype.² Both the HLA-A29 type 1 subtype and the HLA-A29 type 2 subtype respond to serologic tests but migrate differently on 1-dimensional electrofocusing gel electrophoresis. Their results suggested that the HLA-A29 type 2 subtype is the risk factor for birdshot retinochoroidopathy and that the HLA-A29 type 1 subtype actually may be protective against developing the disease. However, Levinson and coauthors found that both subtypes were associated with disease in patients in the United States.³

Nussenblatt and colleagues also found a link with human leukocyte antigen B12 (HLA-B12), which has been confirmed by several other authors.⁴ The link to HLA-B12 is less strong, with a relative risk ratio from 2.7 to 7. Most individuals who are HLA-A29 or HLA-B12 positive do not have birdshot retinochoroidopathy, which obviously implies that other factors are required to provoke the onset of the disease.

Pathogenesis

• Receptor mechanism and concomitant infection: MHC antigen provides a specific cell marker for binding of an infectious microorganism, such as Borrelia burgdorferi and Coxiella burnetii.
• Common embryologic origin: The retina and the pineal gland share a common embryological origin. Experimental studies show that animals immunized with S-Ag and IRBP develop pinealitis in addition to experimental autoimmune uveitis (EAU).

Frequency

United States

Birdshot retinochoroidopathy is a rare disease. There are few reports that address the incidence of birdshot retinochoroidopathy. In the United States, one uveitis clinic reported 7 out of 600 patients (1.2%) with this diagnosis. Since and including 1980, 59 cases have presented to the National Eye Institute (NEI).

International

In Europe, at 14 eye clinics, only 102 cases of birdshot retinochoroidopathy were diagnosed from 1980-1986.

Mortality/Morbidity

Birdshot retinochoroidopathy is a potentially blinding disease. Although some ophthalmologists describe patients with birdshot retinochoroidopathy in whom the disease process runs a relatively benign course, where good visual acuity is preserved with minimal therapy, many patients experience a severe course with loss of functional vision, with permanent macular pathology secondary to uncontrolled inflammation and undertreated macular edema. The author strongly believes that if the disease process of a patient with birdshot retinochoroidopathy demonstrates the ability to cause significant inflammation (particularly if significant vasculitis is present) or vision-affecting macular edema, then it is imperative that treatment options be pursued aggressively to control the disease process.

Race

Most patients are of Caucasian background.

Sex

Gender preference is not clear, as some studies showed predilection for women, but other studies showed no significant sexual predilection.

Age

Birdshot retinochoroidopathy typically occurs during the middle age, presenting at an average age of 50 years, with an age range of 35-70 years.

Clinical

History

The course of birdshot retinochoroidopathy, 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 retinochoroidopathy (n=59). This study showed that the most common complain of NEI population was decreased vision (68%), floaters (29%), nyctalopia (25%), dyschromatopsia (20%), glare (19%), and photopsia (17%).

Other less frequent symptoms are listed below.

• 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% 

Physical

Decreased visual acuity in the initial stages of birdshot retinochoroidopathy is often mild; in many cases, visual acuity is not worse than 20/40 and rarely below 20/80. 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 retinochoroidopathy lesions
  • The classic birdshot retinochoroidopathy 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. 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 retinochoroidopathy 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 retinochoroidopathy 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 retinochoroidopathy lesions may present well after the initial onset of uveitis. In some patients, the disease first presents as a vitritis with vasculitis, with no characteristic fundus lesions. It may take up to 8 years for the characteristic fundus lesions to appear and, hence, occasionally can result in a delayed diagnosis.

Causes

The cause for birdshot retinochoroidopathy is unknown.

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