Sunset glow fundus is a clinical sign observed during an eye exam, not a disease itself. It describes a change in the fundus—the interior back surface of the eye—which indicates an underlying medical condition has affected its pigmented layers. The term “sunset glow” is used because the fundus takes on a distinct, bright, orange-red hue, signaling a specific pathological process has occurred.
The Ocular Appearance Explained
A healthy fundus has a uniform, reddish-orange color from the combination of the light-reflecting retina and the deeper, pigment-rich layers called the retinal pigment epithelium (RPE) and the choroid. The RPE is a layer of pigmented cells under the retina, and the choroid is a network of blood vessels between the retina and the sclera, the white outer layer of the eye. These layers contain melanin, which absorbs excess light and helps provide sharp vision.
The “sunset glow” appearance results from depigmentation, which is a widespread loss of melanin from both the RPE and the choroid. When these pigmented cells are damaged or destroyed, the layers become less opaque. This thinning of the pigment allows the underlying blood vessels of the choroid to become much more visible. The increased visibility of this dense vascular network is what creates the characteristic bright orange-red coloration. This change typically develops over several months.
This depigmentation signifies a structural alteration within the eye caused by the loss of melanocytes, the cells that produce melanin. The resulting appearance provides a clear indication to an ophthalmologist that a specific type of inflammatory or autoimmune process has taken place. The glow is a hallmark of the convalescent, or healing, stage of certain diseases.
Associated Medical Conditions
The sunset glow fundus is most commonly linked to Vogt-Koyanagi-Harada (VKH) disease. VKH is a rare autoimmune disorder where the body’s immune system attacks melanocytes. While these pigment-producing cells are found in the skin, hair, and inner ear, they are highly concentrated in the eyes, particularly within the uvea, which includes the iris, ciliary body, and the choroid. This makes the eyes a primary site of attack in VKH disease.
The immune assault in VKH disease causes severe, bilateral inflammation throughout the uveal tract, a condition known as panuveitis. This inflammation damages and ultimately destroys the melanocytes in the choroid and RPE. As the inflammation subsides and the eye enters a chronic or convalescent phase, the loss of these pigmented cells becomes apparent, leading to the sunset glow fundus. VKH disease can also cause neurological symptoms like headaches, auditory issues, and skin changes like vitiligo or poliosis.
Another, much less common, cause is sympathetic ophthalmia. This condition is an autoimmune response triggered by a penetrating injury or surgery to one eye. The body develops an immune reaction against its ocular tissues, which can then target the uninjured eye, leading to bilateral inflammation similar to that in VKH disease. The resulting damage to melanocytes in the uninjured eye can also cause the fundus depigmentation.
The Diagnostic Process
An ophthalmologist identifies the sunset glow appearance during a dilated fundus examination, where eye drops widen the pupil for a clear view of the back of the eye. While the orange-red fundus is a strong indicator, it is one piece of a larger diagnostic puzzle pointing toward a condition like VKH disease. The doctor will also look for other signs, such as optic nerve swelling or fluid under the retina.
To confirm the underlying cause and assess the extent of the inflammation, advanced imaging tests are often used. Fluorescein angiography involves injecting a dye into the arm and taking pictures as it circulates through the eye’s blood vessels. This test helps identify inflammation and leakage characteristic of VKH disease. Another tool is optical coherence tomography (OCT), a non-invasive test that uses light waves to take cross-section pictures of the retina, revealing fluid or structural changes from the inflammatory process.
Managing the Underlying Disease
Treatment is not directed at the sunset glow fundus itself, as the appearance results from past damage. Instead, medical intervention focuses on managing the underlying autoimmune disease that caused the depigmentation. The primary goal is to control the inflammation, prevent further attacks on melanocytes, and preserve the patient’s vision.
The standard of care for conditions like VKH disease involves prompt anti-inflammatory therapy. Treatment begins with high-dose corticosteroids to quickly suppress the immune response and reduce inflammation. These may be administered orally, intravenously, or through injections around the eye. Following the initial phase, corticosteroids are slowly tapered down. To prevent relapse and avoid the long-term side effects of steroids, patients are often transitioned to other immunosuppressive medications for long-term management. Early and aggressive treatment is associated with a better visual prognosis.