What is Stargardt Disease?
Stargardt disease goes by several names: it can also be called Stargardt macular dystrophy or juvenile macular degeneration. The disease is an inherited condition that affects the retina, which is at the back of the eye. The macula is at the center of the retina, and in this disease, progressive damage occurs, affecting the straight-ahead (also called central) field of vision.1 Often times, vision loss slowly occurs during childhood or adolescence, but for some individuals, it may not occur until adulthood, such as in patients with fundus flavimaculatus.
How common is Stargardt disease?
Stargardt disease is the most common inherited macular dystrophy for both adults and children and affects one in 8,000-10,000 individuals.2 Most affected individuals start having central vision loss in early childhood; others experience vision loss in early adulthood. Less frequent are those who have vision loss in later adulthood, although the later the onset of vision loss, the better the prognosis.2 Some individuals with Stargardt do have later-onset visual deterioration.
What causes Stargardt disease?
The majority of Stargardt disease diagnoses – approximately 95 percent – are caused by autosomal recessive mutations in the ABCA4 gene.1 With autosomal recessive mutations, both parents need to be carriers of the mutation because it takes two copies of the mutation to cause disease.
The most common symptom of the disease is progressive, slow loss of central vision.3 Dark or blurry spots may appear in the central vision, or it might become harder for your eyes to adjust to dark settings when coming in from light, like if you go into a dark house after being out in the sunlight. Some people develop colorblindness as the condition progresses, but not everyone. The progression of Stargardt can vary among individuals, but generally speaking, the earlier the onset of disease, the faster the vision loss.3
Stargardt disease pathophysiology
Your retina has two types of cells which sense light, or photoreceptors, called rods and cones. They convert light into signals that are translated by the brain. Together, rods and cones help you see things in the dark or low light, and also help you see detail and color. Rods are most abundant in the peripheral retina and most cones are found in the macula. Both, however, die off in Stargardt disease, but cones more so.1
Degeneration of the retinal pigment epithelium (RPE)
In Stargardt disease, there is a primary degeneration of the retinal pigment epithelium (RPE), which then causes dysregulation of the photoreceptor cells, and eventually cell death. The RPE is a layer of cells under the retina that takes waste from the photoreceptors and recycles the byproducts of vitamin A that the photoreceptors produce.
The ABCA4 gene
Often seen in Stargardt disease is a mutation in a gene called ABCA4, a gene that makes a protein that usually clears off byproducts of vitamin A from photoreceptors.1 Without ABCA4 and the protein, a fatty substance called lipofuscin accumulates around and in the macula, negatively affecting vision and eventually causing photoreceptors to die.1 Other conditions associated with the mutations in the ABCA4 gene include other retinal dystrophies like cone dystrophy and retinitis pigmentosa.
How is Stargardt disease diagnosed?
Stargardt disease can be diagnosed by an eye exam of the retina by a professional. The lipofuscin deposits are visible yellow flecks and are typically in a ring-shaped pattern coming out from the macula, or may be more diffusely distributed in those with the fundus flavimaculatus variant.1 The eye doctor may also perform general testing like an eye chart, visual field testing, or color testing. Other, more invasive kinds of tests can include a photo of the retina called a fundus photo; electroretinography, or ERG, which measures the response of rods and cones to light; and optical coherence tomography, or OCT, which is a scan that provides cross-section pictures of the retina.1
Right now, there is no treatment for Stargardt disease, unfortunately. Research is being done on gene therapies and drug therapies, as well as stem cell therapies. Since excess light exposure can further damage the retina, individuals with Stargardt disease are urged to wear sunglasses that have UV protection, as well as wide-brimmed hats when going outside.4 They are also urged not to take supplements with large doses of vitamin A, since an excess of this vitamin can actually worsen the disease.4
If you have Stargardt disease, talk with your doctor about the research that is being done, and whether there is a possibility of participating in a clinical trial.
Adaptive devices and tools
Although there is no treatment for the condition, there are adaptive devices to assist you to help with the vision loss associated with Stargardt disease. These include reading devices, magnifying devices, and closed-circuit video magnification systems. Counseling and occupational therapy can aid with the emotional aspect of early vision loss, as well as provide assistance with activities of daily living.