Stargardt Disease (STGD) is an inherited eye disease that causes vision loss. STGD affects the eye’s retina, which is a thin, light-sensitive tissue that lines the back of the eye. Specifically, Stargardt Disease affects a small area of the eye near the center of the retina known as the macula, which is responsible for the sharpness and clarity of vision (“visual acuity”). Over time, STGD impairs central vision which is relied upon to conduct tasks like reading and driving. Stargardt Disease is a progressive disorder that causes increasing vision loss. Some people with the condition become legally blind, however, it is rare to experience complete blindness.
This article covers the prevalence of Stargardt Disease, causes, symptoms, prevention, treatment options such as assistive devices, and more.
What is Stargardt Disease?
Stargardt Disease is a genetic eye disease that results in progressive vision loss. The disease affects the macula region of the retina, which is responsible for central vision and visual acuity. People with STGD usually begin to experience vision loss in early childhood or adolescence. However, some people with STGD do not experience vision problems until they are adults.
There are various terms for Stargardt Disease, including Juvenile Macular Degeneration, Macular Dystrophy with flecks (type 1), and Fundus Flavimaculatus.
The ICD code for Stargardt Disease is H355.
How Does Stargardt Disease Affect the Eye?
Stargardt Disease develops as the result of a problem with the retina, which is the light-sensitive tissue lining the back of the eye. People who have STGD have affected maculas, which sit at the center of the retina, and are responsible for central vision and the ability to see in high resolution and view color. As such, most people with STGD have intact peripheral vision.
Stargardt also affects the rods and cones in the retina. Rods are responsible for vision in dim and dark lighting, while cones detect color and fine detail. Rods sit on the outer edges of the retina; cones are in the macula at the center of the retina. Both rods and cones are affected in patients with Stargardt Disease, but the disease tends to affect cones more strongly.
How Common is Stargardt Disease?
Stargardt Disease is considered a rare inherited retinal disorder. STGD occurs in about 1 in every 8,000 to 10,000 individuals. About 95% of Stargardt cases arise from both parents carrying the mutated gene, although cases can develop if only one parent is a carrier
Progression of Stargardt Disease
Symptoms of STGD typically begin in late childhood or early adulthood. It is difficult to predict when retinal damage will occur or how fast the condition will deteriorate, as these factors vary from person to person. Age of onset does not predict severity or rapidity of disease progression.
As Stargardt Disease advances, visual acuity will decline. Typically, the further deteriorated vision is, the faster it will continue to decline until legal blindness is reached (20/200 or worse while wearing corrective lenses). Most people with STGD can expect an eventual visual acuity of 20/200 to 20/400.
Stargardt Macular Degeneration vs. Age-Related Macular Degeneration
Stargardt Macular Degeneration is a genetic disorder of the retina that affects the macula. It is also known as Juvenile Macular Degeneration, as signs of the disease usually begin in children and young adults. Age-related Macular Degeneration is not genetic, rather it presents as people grow older and their macula deteriorates. Although Age-related Macular Degeneration does not result in profound blindness, it can cause severe vision problems in older people, especially those over the age of 55.
Stargardt Disease is transmitted via autosomal recessive inheritance or autosomal dominant inheritance. In the recessive form of inheritance, STGD is caused by mutations in the ABCA4 gene, where both the parents need to have at least one copy of the mutated gene. In the dominant form of inheritance, mutations in one parent’s ELOVL4 gene can also cause this condition.
The ABCA4 and ELOVL4 genes are responsible for making proteins and clearing toxic substances in the light-sensitive cells of the retina. Mutations in the ABCA4 or ELOVL4 genes effectively stop the removal of toxic byproducts from the retina, which causes harmful build up and the formation of lipofuscin in the eye. Ultimately, this results in the death of cells in the retina, causing loss of central vision.
Signs and Symptoms
The signs and symptoms of Stargardt Disease usually first present in late childhood or early adulthood and progress in severity over time.
The most common symptom of Stargardt Disease is a gradual loss of central vision in both eyes, to the point where it is difficult to perform tasks such as reading, recognizing faces, and driving.
Other symptoms can include:
- Trouble adjusting to low light
- Impaired color vision
- Sensitivity to light
- Grey, black, or blurry spots in the central visual field
An eye specialist can diagnose Stargardt Disease through dilating the pupils and checking for any lipofuscin build-up (yellow flecks on the macula). The size, number, and color of the flecks can vary, but are typically irregular in shape growing outwards from the macula in a ring-like formation.
An optometrist can also measure visual acuity and extent of color vision to assess vision loss associated with Stargardt Disease.
Such tests include:
- Fundus photography – This test captures a photo of the retina to check for yellowish flecks on the macula.
- Electroretinography – This test measures the electrical response of light-sensitive photoreceptors in the eyes.
- Optical coherence tomography – This test checks for any signs of retinal damage.
- Genetic test – A genetic test helps in identifying the presence of mutated genes associated with Stargardt Disease.
There are some preventative measures that can be taken to slow the progression of Stargardt Macular Degeneration:
- Avoid taking supplemental Vitamin A more than the recommended daily amount. Excessive Vitamin A intake may contribute to the build-up of toxic byproducts in the eyes and deteriorate vision.
- Avoid exposure to excessive light by wearing sunglasses with UV protection and a hat with a wide brim to protect the eyes.
- Quit smoking and avoid second-hand smoke to prevent the accumulation of harmful chemical substances in the eyes.
- Avoid heavy drinking as high alcohol consumption can exacerbate retinal damage and contribute to vision problems.
- Consume fresh fruits and vegetables daily for proper nutrition.
- Check your weight and blood pressure regularly to ensure they are healthy.
- Visit an eye specialist at least every 2 years, even if you do not have any vision problems.
The Effects Of Vitamin A on People with Stargardt Disease
Excessive Vitamin A intake is a major risk factor for worsening vision in people with STGD. Rod and cone cells rely on Vitamin A to make important light-sensitive molecules inside the photoreceptor. However, the process releases toxic byproducts, which in healthy people, are removed with the help of the ABCA4 gene. People with Stargardt Disease are unable to remove toxic byproducts due to genetic mutations, which permits the build up of lipofuscin – a fatty substance that forms yellowish flecks in the macula region. Clumps of lipofuscin damage photoreceptor cells, and eventually cause cell death, ultimately resulting in central vision loss that is characteristic of Stargardt Disease.
Currently, there is no available treatment for Stargardt Disease, only prevention of progressive vision loss. The retina is a very fragile part of the eye which is easily prone to damage and tearing, making treatment and surgery difficult. However, researchers are striving to develop gene and drug therapies to treat STGD, with several clinical trials underway.
Clinical Trials Of Gene therapy
There are a number of clinical trials in the United States and Europe that aim to provide gene therapy for STGD. Gene therapy aims to repair or replace the defective ABCA4 gene. However, none of the clinical trials have been approved for commercial use yet.
Human Embryonic Stem Cell Transplant
A human embryonic stem cell transplant aims to replace affected photoreceptor cells with functional photoreceptor cells in patients with Stargardt Disease. Two prospective studies (phase I/phase II clinic) are ongoing in the United States.
There are also some preventive drugs for STGD under development. These pharmaceuticals are targeted towards preventing the build-up of lipofuscin.
Read more further on potential treatments for Stargardt Disease.