Age-related macular degeneration (AMD) is a primary cause of central vision loss, especially in older adults. As the condition progresses, a clinical sign known as a “corona” can appear during eye examinations for advanced AMD. This ophthalmological term is entirely unrelated to the coronavirus. The presence of this corona is a significant indicator for doctors monitoring the progression of the disease. This article will explain what this feature is, how it is identified, and what it signifies for individuals with macular degeneration.
Defining the Corona in Macular Degeneration
In ophthalmology, the term corona describes a halo of increased brightness observed around an area of retinal damage. This is a feature of an advanced form of AMD called Geographic Atrophy (GA), defined by the progressive and irreversible loss of retinal cells. This cell loss creates patches of atrophy where critical cells have died, leading to blind spots. The corona appears specifically at the border of these atrophic patches.
The glow of the corona is technically known as hyperautofluorescence. This fluorescence occurs when the retina is illuminated with blue light during an imaging test. The source is a metabolic waste product called lipofuscin, sometimes called the “age pigment,” which accumulates within the retinal pigment epithelium (RPE) cells. RPE cells are a layer that nourishes the retina’s light-sensing photoreceptors.
An excessive buildup of lipofuscin is a sign of cellular stress and dysfunction within the RPE. These cells are working overtime and are unable to clear waste products effectively, but they have not yet died. The hyperautofluorescent corona represents a transitional zone of stressed RPE cells at the edge of a GA lesion. This makes the corona a visible marker separating the area of cell death from healthier retinal tissue.
Diagnosis and Identification Methods
The primary method used by ophthalmologists to visualize the corona is a non-invasive imaging technique called Fundus Autofluorescence (FAF). This test works by using a specialized camera to shine a safe, low-intensity blue light into the eye. The camera then captures the natural fluorescence that is emitted back from the retina. Because lipofuscin is a key fluorophore, areas with a high concentration of this waste product appear intensely bright in the resulting image. The dead cells within the GA lesion have no lipofuscin, so they appear dark (hypoautofluorescent), creating a stark contrast with the bright ring of the corona.
FAF imaging provides a functional map of the RPE layer, highlighting areas of cellular stress that may not be visible with a standard clinical examination. The process is similar to having a photograph taken of the back of the eye and does not require any injections of dye. The images produced allow clinicians to precisely delineate the borders of the atrophic lesion and identify the corona’s characteristics.
To complement the findings from FAF, doctors use another imaging technology called Optical Coherence Tomography (OCT). While FAF provides a top-down map of fluorescence, OCT provides a high-resolution, cross-sectional view of the retinal layers, much like a microscopic slice. OCT can confirm the areas of retinal thinning and RPE cell loss that define the atrophic lesion. The combination of FAF and OCT gives a comprehensive view of both the metabolic state and the physical structure of the retina.
The Corona’s Role in Disease Progression
The corona is a predictive biomarker for the progression of Geographic Atrophy. The presence and pattern of the hyperautofluorescent ring provide valuable clues about the future course of the disease. Research shows that atrophic lesions in GA expand outward over time, with cell death advancing directly into the area identified as the corona. In essence, the bright ring seen today predicts the location of future atrophy.
Ophthalmologists have classified the corona into several patterns based on its appearance in FAF imaging, and these patterns are correlated with different rates of GA progression. A “focal” pattern, with small, isolated spots of hyperautofluorescence at the lesion border, is associated with a slower rate of growth. A “banded” pattern, which appears as a continuous, bright ring encircling the atrophy, suggests a more moderate speed of expansion.
The most aggressive form is the “diffuse” pattern, where hyperautofluorescence extends more widely from the lesion border. Patients with banded or diffuse patterns experience a more rapid enlargement of their atrophic lesions compared to those with focal patterns. By analyzing the corona’s characteristics, clinicians can better forecast the speed of disease progression, helping to set expectations and guide monitoring frequency.
Management and Current Treatments for Geographic Atrophy
Since the corona is a feature of Geographic Atrophy, management strategies are focused on the underlying GA. For many years, treatment was limited to observation and low-vision aids. However, the understanding of GA as a disease driven by an overactive inflammatory pathway, the complement cascade, has led to new therapeutic options. In 2023, two drugs were approved to treat GA: pegcetacoplan (Syfovre) and avacincaptad pegol (Izervay).
These medications are administered as injections directly into the eye. They function as complement inhibitors, designed to calm the inflammatory process that contributes to RPE cell death. Pegcetacoplan targets a protein earlier in the cascade called C3, while avacincaptad pegol targets a downstream protein called C5. By blocking these components, the drugs slow down the entire inflammatory chain reaction. Clinical trials show both treatments can reduce the rate of GA lesion growth by around 14% to 20% over a year.
It is important to note that these treatments slow the progression of atrophy; they do not reverse existing damage or improve lost vision. Comprehensive management also includes regular monitoring with FAF and OCT to track lesion growth. Patients are often counseled on the use of AREDS2 vitamin supplements, which may help reduce the risk of progression. Low-vision rehabilitation, including training with magnification devices, can help individuals maximize their remaining vision and maintain their quality of life.