Adult Vitelliform Dystrophy (AVD) is a progressive, late-onset macular dystrophy that typically begins in middle age. It affects the macula, the central part of the retina responsible for sharp, detailed central vision. AVD is characterized by the accumulation of a yellowish deposit beneath the retinal pigment epithelium (RPE). As a genetic disorder affecting the central retina, it often leads to a gradual decline in the ability to see clearly.
Defining the Condition
Adult Vitelliform Dystrophy is defined by the presence of a characteristic vitelliform lesion in the macula. This deposit is often described as resembling an “egg yolk” due to its round, yellow, and slightly elevated appearance during an eye examination. The lesion is primarily composed of lipofuscin, a fatty, yellowish pigment that accumulates within and beneath the Retinal Pigment Epithelium (RPE) layer. The buildup of this material disrupts the RPE’s function of supporting the light-sensing photoreceptor cells.
The “Adult” designation distinguishes this condition from the more severe, childhood-onset Best Vitelliform Macular Dystrophy (Best disease). AVD typically presents between the third and fifth decades of life, compared to Best disease, which starts much earlier. The lesions in AVD are generally smaller, more confined to the fovea, and the overall course of the disease is usually milder.
Although AVD can affect both eyes, the progression is often asymmetric, meaning the lesions may be at different stages in each eye. As the condition progresses, the “egg yolk” appearance may change, sometimes evolving into a “scrambled egg” appearance as the material disperses or leading to atrophy.
Genetic Basis and Causes
Adult Vitelliform Dystrophy is considered a genetic condition, though the cause is often unknown in the majority of cases. When a genetic link is identified, it is frequently associated with mutations in the PRPH2 gene (also known as RDS). This gene provides instructions for making peripherin 2, a protein located on the surface of photoreceptor cells that helps maintain the structure of their light-sensing outer segments.
A malfunction in the peripherin 2 protein leads to the improper processing of waste products, resulting in the abnormal accumulation of lipofuscin. This accumulation stresses and damages the adjacent RPE cells, leading to the formation of the characteristic vitelliform lesion. The inheritance pattern for AVD, when a gene is involved, is often autosomal dominant, meaning only one copy of the altered gene is needed to potentially develop the condition.
Other genes, including BEST1, IMPG1, and IMPG2, have also been linked to some cases of AVD. However, the vast number of sporadic cases suggests that other genetic or environmental factors play a significant role in its development. Researchers continue to investigate these genetic overlaps, particularly with common conditions like age-related macular degeneration (AMD).
Symptoms, Diagnostic Tools, and Prognosis
Symptoms of AVD are often subtle in the early stages, and many individuals remain visually asymptomatic for years. The condition is often discovered incidentally during a routine eye exam. When symptoms do appear, they are typically mild and localized to the central field of vision. These may include slightly blurred central vision, difficulty reading, or metamorphopsia, where straight lines appear wavy or distorted.
Specific diagnostic tools are used to confirm the presence of the vitelliform lesion and rule out other macular diseases. Optical Coherence Tomography (OCT) is a non-invasive imaging method that provides cross-sectional views of the retina. OCT clearly visualizes the subretinal material, appearing as a dome-shaped, hyper-reflective deposit located between the RPE and the photoreceptor layer.
Fundus Autofluorescence (FAF) imaging is another important tool, as it uses the natural fluorescence of lipofuscin to highlight the lesion. The vitelliform material typically shows high autofluorescence, which helps track the lesion’s size and stage of progression.
Differentiating AVD from Best Disease
To differentiate AVD from the juvenile Best disease, an Electrooculogram (EOG) test is often performed. Unlike Best disease, which shows a markedly abnormal EOG result, AVD is characterized by a typically normal EOG, a key distinction for an accurate diagnosis.
The prognosis for AVD is generally favorable compared to other macular dystrophies. Vision loss is usually slow and progressive, and many patients maintain functional vision for decades. Significant reduction in visual acuity often occurs late in the disease course, typically associated with the development of macular atrophy or a complication called Choroidal Neovascularization.
Current Management Approaches
Currently, there is no known treatment to reverse the underlying degenerative process of Adult Vitelliform Dystrophy. Management focuses on regular monitoring and the prompt treatment of complications that can lead to rapid vision loss. Comprehensive eye examinations, often including OCT and FAF imaging, are recommended once or twice a year to track the lesion’s progression.
The most significant complication requiring intervention is Choroidal Neovascularization (CNV), which is the growth of abnormal, fragile blood vessels under the retina. These vessels can leak fluid and blood, causing a sudden and severe drop in central vision. If CNV develops, the standard treatment involves anti-VEGF injections (such as ranibizumab or bevacizumab) administered directly into the eye. These injections control the growth of new blood vessels and stabilize or improve affected vision.
While specific treatments for the dystrophy itself are unavailable, general lifestyle recommendations are suggested to support overall macular health. These include:
- Protecting the eyes from harmful UV radiation.
- Avoiding smoking.
- Maintaining a healthy diet rich in antioxidants.
For individuals who experience significant central vision impairment, a referral to a low vision specialist can be beneficial. These specialists provide aids and rehabilitation services to help optimize remaining sight and maintain quality of life.