Best disease is an eye condition that people inherit from their parents. It starts during childhood and causes progressive vision loss later in life, developing in six stages.

Best disease, also known as Best vitelliform macular dystrophy (BVMD), is an eye condition that results in progressive vision loss.

The condition affects the retina, which is a light-sensitive layer of tissue in the eye. Specifically, it affects the macula, which is a small area in the center of the retina. The macula is responsible for central vision, color vision, and fine detail.

BVMD leads to the buildup of a fatty yellow pigment called lipofuscin. When this substance accumulates, it can damage cells that are important for clear vision.

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Best disease is the childhood-onset form of vitelliform macular dystrophy (VMD). As such, some doctors refer to it as BVMD. VMD refers to a genetic eye condition that causes progressive vision loss.

BVMD affects the part of the eye most responsible for central vision, known as the macula. As such, the condition often leads to distorted or blurred vision but does not usually affect side vision. The characteristic feature of VMD is the presence of a vitelliform lesion on the macula. The term “vitelliform” is Latin for “egg yolk.”

The name Best disease derives from Dr. Friedrich Best, who identified the condition in the early 1900s. Subsequently, the characteristic gene in which variations can result in BVMD is known as the BEST1 gene.

According to a 2023 study, around 1 in 70,000 people in the United States have Best disease. This makes it one of the most common inherited macular diseases, yet it is still rare among other eye problems. The childhood version is more common — people usually start to develop Best disease between 5 and 10 years of age.

Best disease starts developing in childhood before worsening for some people later in life. However, the age and severity at which a person first develops symptoms can differ between individuals.

Adult-onset VMD begins later in life, usually between 30 and 50 years of age. It tends to worsen vision loss as a person ages. However, it generally does not cause vision problems outside of a mild to moderate decrease in visual sharpness.

While they have similar features, they each cause distinct changes to the macula that an eye doctor can detect during an eye examination.

Best disease typically occurs due to changes in a gene called BEST1. However, evidence notes that other genes, such as PRPH2, IMPG1, and IMPG2, also play a role in the development of the condition.

The BEST1 gene guides the production of bestrophin, a protein that transfers chlorine atoms to and from retina cells. If the cells undergo a change or alteration, the channels through which chlorine atoms move cannot control the chloride flow.

Currently, researchers are unsure how these changes to the flow of chloride result in BVMD. However, these alterations cause a buildup of a fatty yellow substance known as lipofuscin. When this substance accumulates in the macula, it damages the cells and leads to vision loss.

Best disease passes from parents to children in an autosomal dominant pattern. This means that a child only needs a gene from one parent to develop the condition.

Best disease develops in six distinct stages, with doctors considering the final stage, choroidal neovascularization (CNV), to be a complication. CNV involves the creation of new blood vessels in the choroid layer of the eye.

The six stages include:

  1. Previtelliform: At this stage, a person may still have good vision, and only very subtle changes are present. The name refers to this stage occurring before the formation of the characteristic egg yolk lesion.
  2. Vitelliform: This is the most common stage in new diagnoses of Best disease. A scan or examination will likely show a pocket of yellow material in the retina’s center, known as an egg yolk lesion. A person with stage 2 Best disease will still have typical or mildly reduced vision.
  3. Pseudohypopyon: During this stage, the egg yolk moves toward the bottom of the eye, creating layers of fluid in which the base is yellow, but the top is clear. Vision is similar to stage 2.
  4. Vitelleruptive: The layers of fluid spread throughout the retina. Some eye doctors call this a scrambled egg appearance, and vision may be the same as or slightly worse than stage 2.
  5. Atrophic: The yellow material is no longer present. Instead, an area of tissue damage and atypical tint in the eye develops, similar to the symptoms of age-related macular degeneration (AMD). Atrophic Best disease usually develops after 40 years of age.
  6. CNV: At this stage, new blood vessels form on the retina and bleed. This occurs for around 1 in 5 people with Best disease and causes significant vision loss.

In the final two stages, visual sharpness may be 20/30 to 20/200, up to ten times worse than average 20/20 vision. However, according to a 2023 study, a person may not progress through each stage in the usual order.

The condition rarely affects visual sharpness, especially in the early stages. Many people find out they have Best disease during routine examinations. However, the following symptoms may develop over time if a person reaches the later stages:

  • blurry vision
  • reduced sharpness of vision
  • seeing objects as having an altered shape to the one they have in reality

Several scans and tests can help an ophthalmologist, who is an eye care specialist, diagnose Best disease. These may include:

  • Electrooculogram: This test measures the eye’s response to light by measuring electrical signals it generates while adjusting to different light levels. A low score on this test using a number, known as the Arden ratio, may suggest the presence of Best disease.
  • Electroretinogram: This checks how the retina responds after exposure to light.
  • Fluorescein angiogram: An ophthalmologist injects a dye into the eye and then produces images of the eye. These show any blood flow issues as the dye travels through the eye.
  • Fundus autofluorescence: This shows how some parts of the retina naturally glow to highlight damaged or diseased areas. This can highlight Best disease’s trademark yellow mass on the macula.
  • Optical coherence tomography: This approach uses light to create digital images of the retina’s layers and can show abnormalities.

People and their parents or siblings may also undergo testing for variations in the BEST1 to confirm a Best disease diagnosis. A test known as molecular genetic sequencing is effective at diagnosing the disease in 96% of those with a family history or 50% to 75% of those without.

Currently, no cure is available for Best disease. However, for people whose disease progresses to CNV, anti-vascular endothelial growth factor (anti-VEGF) injections can help prevent new blood vessels from forming on the macula.

Regular eye exams are necessary to monitor disease progression. To manage vision changes, a person may use vision correction, devices, or aids to support daily function. People with large lesions due to Best disease also need to avoid strenuous activity or contact sports, as head or eye injury may cause lesions to burst.

As a genetic condition, people with Best disease and their families may benefit from genetic counseling. This can provide information on the risk of passing on the disease and helpful resources around testing.

Best disease is a progressive, inherited macular condition. It typically occurs due to an alteration in the BEST1 gene. This leads to a buildup of lipofuscin on the retina, which damages the macula. Best disease usually occurs in childhood, between the ages of 3 to 15. As the name suggests, this form has an earlier onset than the adult version of the disease.

It develops in six stages before causing severe vision loss due to choroidal neovascularization (CNV). Several tests and scans are available to help medical professionals diagnose the condition. At present, no treatment is available, but anti-VEGF injection can prevent CNV from worsening.