Birdshot Chorioretinopathy: Causes, Symptoms, and Management

Introduction:

The eyes are the organs that help a living being to see. There are several parts of the eye, such as the iris (the colored part of the eye), the cornea (a clear layer that extends over the iris), the sclera (the white part of the eye), the pupil (the black circle in the middle of the iris), the lens (behind the pupil), and the retina (a set of cells that lines inside the eye). The retina captures and converts the light that enters the eye and depicts the images an individual sees. The light reaches through the lens and hits the retina. Photoreceptors (cells inside the retina) change the light into electrical signals. If the retina is damaged, the eyes can see, but the brain cannot receive the information needed for creating the images.

What Is Birdshot Chorioretinopathy?

Birdshot chorioretinopathy is a rare eye inflammation and a chronic condition that can lead to permanent blindness. It was discovered in 1949 and was named birdshot chorioretinopathy for its cream and orange spots in the retina. Several other names for this condition include birdshot chorioretinitis, birdshot retinochoroiditis (inflammation of the retina and the choroid), and birdshot uveitis. Birdshot chorioretinopathy is a form of uveitis. Uveitis is a term given to a group of disorders that causes eye redness and inflammation. Birdshot chorioretinopathy causes swelling in the retina and choroid (connects the retina to the white part of the eye). This condition affects women more than men and usually occurs in the 30 to 60 years of age group and rarely affects children. If this condition is left untreated, that can lead to irreversible blindness.

What Causes Birdshot Chorioretinopathy?

The exact cause of birdshot chorioretinopathy is unknown, but it is thought that it can occur due to autoimmunity. An autoimmune disease occurs when the immune system mistakenly attacks the healthy cells instead of protecting them. Around 90 percent of birdshot chorioretinopathy is inherited, which means it is received from the parents. Human leukocyte antigens (HLA) are seen to be involved in causing this condition.

• Human Leukocyte Antigen: This antigen is a type of molecule that is found on the cells' surface cells. These antigens help the immune system in responding to foreign substances. When the immune system unknowingly damages healthy cells, one type of HLA, which is known as HLA-A29, also triggers the immune system. In some cases, an individual is born with this antigen but does not get this disorder.

What Are the Symptoms of Birdshot Chorioretinopathy?

The symptoms vary in each individual as it is a progressive condition that can worsen with time. Some of the common symptoms include:

• Ocular hypertension (high eye pressure).

• Blurry vision.

• Decreased night vision.

• Difficulty in differentiating particular colors (dyschromatopsia).

• Sensitive to bright colors or light (photophobia).

• Flashes or flickering lights.

• In severe cases, it can cause cataracts (the lens of the eye becomes foggy).

• Glaucoma (a condition that damages the optic nerve).

What Are the Different Modalities Through Which Birdshot Chorioretinopathy Is Diagnosed?

Some of the modalities through which this condition can be diagnosed include:

• Clinical Examination - A clinical examination is the first and essential step to diagnosing birdshot chorioretinopathy. A doctor will examine the patient’s eye and check the complete medical history to evaluate the involvement of autoimmune conditions.

• Indocyanine Green Angiography (ICG) - It is used to detect the choroid and shows the hyper lucent lesion. An ICG dye is injected through the arm’s vein, which reaches the eye through the blood vessels. When the dye flows through the eye’s blood vessels, the images are captured to note the blood flow. The procedure is completed in 10 to 20 minutes and does not cause any allergic reactions.

• Blood Test - A blood test is done to diagnose the HLA-A29 antigen in the body. A fine needle is inserted in the arm’s vein, and a small amount of blood is drawn out in a vial. The sample is then sent to the laboratory for further testing.

• Electroretinography (ERG) - An ERG is a test that checks the electrical response of light-sensitive cells which are present in the retina of the eyes. Numbing drops are given, and the eyes are opened with a device called a speculum, and an electrode (electrical sensor) is placed on each eye. The electrode measures the electrical activity of the retina when light is passed through it.

What Are the Other Conditions Similar to Birdshot Chorioretinopathy?

Some of the other conditions similar to birdshot chorioretinopathy are listed below:

• Infectious - Some infectious conditions are tuberculosis (an infectious disease that affects the lungs) and syphilis (a bacterial infection that occurs through sexual contact).

• Non-Infectious - Some non-infectious conditions are sarcoidosis (tiny inflammatory cell growth in any part of the body) and sympathetic ophthalmia (a rare granulomatous uveitis caused by exposed ocular antigen from any trauma).

How Is Birdshot Chorioretinopathy Managed?

This condition has no permanent cure, but the treatment focuses on reducing the severity.

• Corticosteroids are given to reduce the inflammation of the eye. This steroid can be given in the form of eye drops, medication, or intravenously (IV).

• Immunomodulatory therapy is considered to reduce ocular inflammation.

• Corticosteroid implant surgery is done in which corticosteroid implants are placed in the eyes of patients who are unable to handle the immunomodulatory therapy.

Conclusion:

Birdshot chorioretinopathy is a rare inherited eye disorder. It is caused due to autoimmune disorder that damages healthy cells and is also due to HLA-A29 antigens. It can cause inflammation, swelling, flashing, and blurry vision. It can be diagnosed through various methods like blood tests and electroretinography (ERG). Early diagnosis is necessary as it will help avoid complications like permanent blindness. Treatment focuses on giving corticosteroids and immunomodulatory therapy to reduce inflammation and swelling. When the treatment is taken regularly, it will help lower the effects of the symptoms and lead a better healthy life.