Best disease, also recognized as vitelliform macular dystrophy, is an inherited eye condition that primarily impacts the macula, a small area at the center of the retina responsible for sharp, detailed vision. This condition leads to a progressive loss of central vision. It is a rare disorder, and its effects on vision can vary significantly among individuals.
The Genetic Basis of Best Disease
Best disease originates from specific changes, or mutations, within the `BEST1` gene. This gene provides instructions for creating a protein known as bestrophin, which plays a role in the normal functioning of the retinal pigment epithelium (RPE). The RPE is a layer of cells located beneath the retina that provides support for the light-sensing photoreceptor cells. When the `BEST1` gene is mutated, the bestrophin protein may not function correctly, leading to issues with fluid and ion transport within the RPE. This dysfunction can cause an accumulation of a fatty yellow pigment called lipofuscin beneath and within the RPE cells, particularly in the macula.
The inheritance pattern for Best disease is autosomal dominant. This means that only one copy of the mutated `BEST1` gene is needed for a person to develop the condition. If a parent has Best disease, each of their children has a 50% chance of inheriting the mutated gene and potentially developing the disorder.
Symptoms and Disease Progression
Individuals with Best disease often experience a range of visual symptoms, which can include blurry vision and a noticeable decline in their central visual acuity. Many also report metamorphopsia, where straight lines appear wavy or distorted. The severity and onset of these symptoms can vary widely among affected individuals, even within the same family.
The progression of Best disease is characterized by distinct clinical stages. The initial phase, known as the previtelliform stage, might show no visible changes in the retina, yet specialized tests can already detect retinal dysfunction. This can occur in asymptomatic children or infants.
The disease often advances to the vitelliform stage. During this stage, a yellowish, dome-shaped lesion forms under the macula, closely resembling an “egg yolk”. Visual acuity may remain relatively good for many years.
As the condition progresses, the vitelliform lesion can rupture, leading to what is sometimes described as a “scrambled egg” appearance in the macula. This vitelliruptive stage often coincides with a more significant decline in central vision. The final stage involves atrophy, or degeneration, of the retinal pigment epithelium and photoreceptors in the macular area. This atrophic stage can further reduce central vision.
Diagnosis and Management
Diagnosis of Best disease begins with a comprehensive eye examination, where an ophthalmologist observes characteristic macular changes. Optical Coherence Tomography (OCT) is used to gain detailed views of retinal layers and confirm subretinal fluid or pigment accumulation. This imaging technique provides cross-sectional scans, revealing disease extent.
Electrooculography (EOG) is another diagnostic tool, measuring retinal pigment epithelium electrical activity. A hallmark of Best disease is a significantly abnormal EOG, even in individuals without visible symptoms or noticeable vision loss. Genetic testing can further confirm the diagnosis by identifying `BEST1` gene mutations, which also informs prognosis.
Currently, no direct treatment corrects the underlying genetic mutation in Best disease. Management focuses on addressing complications, primarily choroidal neovascularization (CNV), involving abnormal blood vessel growth beneath the macula. These fragile vessels can leak, causing sudden vision loss.
If CNV develops, treatment involves anti-VEGF injections. These medications block proteins that promote abnormal blood vessel growth, helping to preserve vision. Regular monitoring by an eye care professional is important for early detection of changes. Individuals may also benefit from low-vision aids, such as magnifiers, to assist with daily tasks.
Long-Term Outlook
The long-term outlook for individuals with Best disease is variable, with vision loss occurring gradually over many years. The degree of visual impairment differs significantly from person to person, even among family members who share the same genetic mutation. While some individuals may experience substantial central vision decline, others might retain relatively good vision throughout their lives.
For many, central vision may deteriorate to around 20/100 later in life. Best disease primarily affects central vision and does not lead to complete blindness. Peripheral, or side, vision remains preserved, allowing individuals to navigate their surroundings. The condition may not affect both eyes equally, with some individuals maintaining better central vision in one eye.