What Is Stargardt's Disease?
Stargardt's disease is the most common form of inherited juvenile macular degeneration. It is characterized by a reduction of central vision with a preservation of peripheral (side) vision.
Stargardt's disease, also known as fundus flavimaculatus, is usually diagnosed in individuals under the age of 20 when decreased central vision is first noticed. On examination, the retina of an affected individual shows a macular lesion surrounded by yellow-white flecks, or spots, with irregular shapes. The retina consists of layers of light-sensing cells that line the inner back wall of the eye and are important in normal vision. The macula is found in the center of the retina and is responsible for the fine, detailed central vision used in reading and color vision.
The progression of visual loss is variable. One study of 95 individuals with Stargardt's disease showed that once a visual acuity of 20/40 was reached, there was often rapid progression of additional visual loss until acuity was reduced to 20/200 (legal blindness). By age 50, approximately 50 percent of all those studied had visual acuities of 20/200 or worse. Eventually, almost all individuals with Stargardt's disease are expected to have visual acuities in the range of 20/200 to 20/400. The reduced visual acuity due to Stargardt's disease cannot be corrected with prescription eyeglasses or contact lenses. In late stages of the disease, there may also be noticeable impairment of color vision.
What Causes Stargardt's Disease
In 1997, Foundation Fighting Blindness researchers isolated the gene for Stargardt's disease. The ABCR gene produces a protein involved in energy transport to and from photoreceptor cells in the retina. Mutations in the ABCR gene, which cause Stargardt's disease, produce a dysfunctional protein that cannot perform its transport function. As a result, photoreceptor cells degenerate and vision loss occurs.
Bilateral, decreased central vision in childhood or young adulthood
Visual acuity may start at the 20/40 level and later decline to 20/200 or slightly worse
Central scotoma (blind spot in central vision)
Abnormal color vision
Photophobia -- an abnormal visual intolerance of light
At the beginning stage of the disease, the retina may appear normal upon routine examination. As the disease progresses, clinical signs of the condition can be viewed with ophthalmoscopy. Your ophthalmologist or retinal specialist may perform additional common diagnostic procedures -- visual acuity tests, color vision testing, the Amsler grid test or an automated macular field test to assess vision. Other tests may also be ordered, such as an electrodiagnostic test to examine macular function.
As with macular degeneration patients, fluorescein angiography may be necessary to document the pattern of blood vessels and determine whether dye leaks from the vessels. A doctor can determine which areas of the macula are damaged and whether there are abnormal blood vessels to be treated.
Stargardt's disease, an early-onset form of macular degeneration, is an inherited disease. The condition is programmed into your cells at conception. It is not caused by injury, infection or exposure to a toxic agent. Because Stargardt's disease is an inherited condition, there is nothing that can be done to reduce the risk of developing the disease.
However, recent findings in rodent models of Stargardt's disease find that unprotected, prolonged exposure to light can accelerate vision loss. Therefore, The Foundation Fighting Blindness strongly recommends that patients with Stargardt's disease wear brimmed hats or visors and sunglasses when outdoors.
Stargardt's disease is an autosomal recessive disease. In autosomal recessive diseases, unaffected parents, who are carriers, have one gene with a disease-causing mutation paired with one normal gene. Each of their children then has a 25 percent chance (or one chance in four) of inheriting the two diseased genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene.
What You Can Do to Reduce Risk
Unfortunately, there is no treatment that has been proven to improve the visual loss or to retard the progressing of the disease.
The discovery of the ABCR gene now allows researchers to study the underlying biochemical interactions that result from mutations in this gene. Understanding how genetic mutations lead to retinal degeneration is critical for the development of experimental therapies. Although there is currently no treatment for Stargardt's disease, individuals benefit from the use of low vision aids and orientation and mobility training.