What is Stargardt disease?
Stargardt disease is an inherited eye disorder that causes vision loss.
Specifically, Stargardt disease affects the clarity and sharpness of vision, known as visual acuity. Eye doctors describe normal visual acuity as 20/20 vision, determined by the smallest print size healthy sighted people can read on an eye chart 20 feet away. Visual acuity will deteriorate to 20/200 or worse for most people with the eye condition, according to the National Eye Institute, which the U.S. Social Security Administration (SSA) defines as legally blind. While Stargardt disease may cause vision loss to the point of being legally blind, it rarely causes complete blindness.
Vision loss associated with the disease typically begins in childhood, but vision problems may begin in adults with some forms of the condition. Stargardt disease occurs in about 1 in every 8,000 to 10,000 births, according to the portal for rare diseases and orphan drugs, Orphanet.
Signs and Symptoms
The signs and symptoms of Stargardt disease typically develop in late childhood or early adulthood. Symptoms typically worsen over time.
The primary symptom of Stargardt disease is loss of vision in both eyes that usually develops very slowly over time. Specifically, the disease causes loss of central vision used for close-up work, such as reading, driving, and recognizing faces.
In addition to central vision loss, people living with this eye condition often have trouble with night vision. This can make it difficult to get around in low light. Some people with Stargardt also have impaired color vision.
Stargardt disease develops as the result of a problem with the retina, which is the light-sensitive tissue lining the back of the eye. Light enters the eye, carrying visual information about the world, and strikes the retina. Special photoreceptors in the retina, known as cones and rods, absorb the light and convert the information into pulses. The optic nerve carries these pulses to the brain, which converts the pulses into a visual image.
Specifically, Stargardt disease affects the macula, which sits at the center of the retina. The macula is responsible for central vision and for seeing close-up objects clearly.
Stargardt also affects the rods and cones. 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 the rods and cones die in patients with Stargardt disease, but the disease tends to affect cones more strongly in most cases.
Meet Yvonne Felix, eSight user living with Stargardt disease. Click video to watch her story
Rods and cones use vitamin A to make the important light-sensitive molecules inside the photoreceptors. Unfortunately, the manufacture of vitamin A creates harmful byproducts. The human body normally makes a protein that clears away these byproducts.
In people with Stargardt disease, though, mutations in the gene that makes the protein can prevent the body from clearing away the vitamin A byproducts. Clumps of lipofuscin, a fatty substance that forms yellowish flecks, can accumulate in the cells that lack the protein. These clumps can build up in and around the macula to damage photoreceptor cells and impair central vision. The more the clumps build up, the worse vision gets. In time, the clumps lead to the death of the photoreceptors and very poor visual acuity.
Stargardt disease is an inherited condition, which means it is passed down in families. About 95 percent of Stargardt disease cases occur when both parents carry the gene mutation.
Diagnosis and Support
To diagnose Stargardt disease, eye care professionals look for lipofuscin, which usually appear as yellow flecks on the macula. The flecks typically have an irregular shape and usually extend outward from the macula in a ring-like pattern. The size, number, appearance and color of the lipofuscin flecks vary.
An eye care professional may also test the patient’s visual field to identify loss of central vision and perform tests to evaluate the patient’s color vision. Other tests, such as a fundus photo of the retina that may reveal the presence of fundus, electroretinography (ERG) to measure the electrical response of rods and cones to light, and optical coherence tomography (OCT) that looks for damage to the retina.
There is currently no treatment for Stargardt disease, but there are steps patients can take to reduce the presence of the lipofuscin that contributes to symptoms. Eye care professionals often suggest patients with Stargardt disease wear dark glasses and hats when venturing out into bright lights to reduce the accumulation of lipofuscin. People with Stargardt disease should avoid smoking cigarettes and exposure to secondhand smoke. Those with the condition should also avoid vitamin A supplements altogether, or take them only under a doctor’s supervision.
People with Stargardt disease may benefit from the use of low vision aids that make it easier to carry out daily activities and remain independent. Low-tech aids for visually impaired include glasses and hand-held lenses. High tech vision aids include eSight, a Class 1 Medical Device that provides a non-surgical, wearable low vision aid. It works by stimulating activity from the remaining photoreceptors in the user’s eyes, which provides the brain with the visual information it needs to compensate for the gaps in the field of view. Many users of eSight live with Stargardt and use the device and other technologies to live an active and independent life.
While Stargardt is a vision-robbing condition, advances in medicine, technology and low vision aids are helping people see clearly every day.