Vitelliform macular dystrophy, often called Best disease, is a hereditary eye condition that affects the macula. The macula is the small, central portion of the retina responsible for sharp, detailed central vision for reading and recognizing faces. This disorder leads to a gradual decline in vision, although the rate and severity can vary significantly. While it affects central vision, peripheral vision remains unaffected.
Genetic Origins and Inheritance
Vitelliform macular dystrophy is a genetic disorder caused by a mutation in the BEST1 gene. This gene holds the instructions for making bestrophin-1, a protein that functions as a channel controlling ion movement across the retinal pigment epithelium (RPE). The RPE is a layer of cells that nourishes and supports the retina’s light-sensing photoreceptor cells.
A defect in the bestrophin-1 protein disrupts the transport of ions and fluid, leading to an accumulation of a yellow, fatty substance called lipofuscin between the RPE and photoreceptor cells. This buildup causes the characteristic lesions seen in the disease and eventually damages the macula. The condition is passed down through families in an autosomal dominant inheritance pattern.
This autosomal dominant pattern means inheriting just one copy of the mutated BEST1 gene from one parent is sufficient to cause the condition. An individual with Best disease has a 50% chance of passing the mutated gene on to each of their children. The age of onset and specific symptoms can differ greatly even among members of the same family.
Stages and Associated Symptoms
The progression of Vitelliform Macular Dystrophy occurs in distinct stages. The first is the pre-vitelliform stage, where an individual has no symptoms and vision is normal. The characteristic yellow lesion has not yet formed, but specialized testing can detect underlying abnormalities in the retinal pigment epithelium.
The next is the vitelliform stage, which means “egg-shaped.” This stage is marked by a distinct, round, yellow lesion in the macula that resembles an egg yolk. This lesion is the visible accumulation of lipofuscin. Visual acuity during this stage is often good, ranging from normal to mildly blurred.
The lesion can then evolve into the pseudohypopyon stage, where the yellow material forms a cyst-like structure. Next is the vitelliruptive or “scrambled-egg” stage, where the lesion breaks apart, causing the lipofuscin to spread. During this phase, individuals often notice a more significant decline in vision, such as increased blurriness or metamorphopsia, where straight lines appear wavy.
The final phase is the atrophic stage, characterized by the loss of RPE and photoreceptor cells, which leads to a patch of retinal thinning. This damage results in a significant and often permanent loss of central vision. Not everyone will progress through all stages, and the timeline for these changes varies widely.
The Diagnostic Process
An ophthalmologist confirms a diagnosis of Vitelliform Macular Dystrophy using several examinations and imaging tests:
- A dilated fundus examination, which allows a doctor to view the back of the eye to identify the classic yellow, egg yolk-like lesion.
- Optical Coherence Tomography (OCT) provides a high-resolution, cross-sectional image of the retina, allowing the doctor to see the precise location of the lipofuscin deposit and assess structural changes.
- Fundus Autofluorescence (FAF) uses a special light to highlight lipofuscin, which appears intensely bright, helping to confirm the lesion’s composition and extent.
- An Electrooculogram (EOG) measures the electrical potential generated by the RPE; the results are markedly abnormal in individuals with a BEST1 mutation, even in early stages, making it a hallmark of the condition.
Monitoring and Management Strategies
There is no cure to reverse or halt the progression of Vitelliform Macular Dystrophy. Management focuses on regular monitoring to track the disease and address complications. This involves a consistent schedule of appointments with an ophthalmologist to detect potential problems early.
An effective tool for patients to use at home is the Amsler grid. This grid of straight lines helps individuals monitor for changes in their central vision. Covering one eye and staring at the central dot, the patient looks for any new wavy, blurry, or missing lines, which could indicate a worsening of the condition and should prompt a visit to their eye doctor.
A significant complication that can occur in the later stages is choroidal neovascularization (CNV). This involves the growth of new, abnormal blood vessels from the choroid layer beneath the retina. These vessels can leak fluid and blood, causing rapid and severe vision loss, and are also seen in wet age-related macular degeneration.
CNV can be treated with injections of anti-VEGF medication directly into the eye. These drugs block the signals that promote the growth of leaky blood vessels, which can help stabilize or improve vision. Timely detection and treatment of CNV through regular monitoring is the primary way to preserve as much central vision as possible.