What is Stargardt macular dystrophy?
Stargardt macular dystrophy (Stargardt disease) is an inherited eye disorder that causes loss of central vision in younger people. It affects the macula, the small portion of the retina responsible for central vision and seeing colour and fine details. It is a juvenile macular dystrophy and should not be confused with age-related macular degeneration, even though the symptoms are very similar.
The macula is a small area located in the central area of the retina. The retina itself is a delicate layer of tissue lining the inside and back of the eye. It contains photoreceptors called cones. There are millions of these tiny cells, and they are responsible for detecting colour and fine detail, which are necessary for activities such as reading and driving. Rod cells are responsible for detecting light and are used to see in dimly lit circumstances. These cells are abundant in the outer areas of the retina.
What are the symptoms of Stargardt macular dystrophy?
Individuals with Stargardt report:
* loss of the ability to see fine detail
* gradual loss of the ability to distinguish faces
* difficulty distinguishing colours.
The amount of vision loss varies from person to person. Many individuals with Stargardt are diagnosed before the age of 20; however, some may not notice any significant vision loss before the age of 30 or 40. The effect on sight will vary from minor to complete loss of central vision.
Reduced visual acuity (the ability to see clearly) caused by Stargardt cannot be corrected with prescription eyeglasses or contact lenses. While most people with Stargardt may experience considerable loss of sight over a number of years, total loss of sight is rare. In fact, peripheral (side vision) and night vision, as a general rule, remain intact.
What causes the vision loss?
Stargardt macular dystrophy results in the progressive loss of cone cells. These photoreceptors are responsible for much of our central and colour vision, and our ability to see fine details. The gradual loss of the cone cells may start as early as age six, and it progresses over a period of years.
Defects in the ABCR Gene
Scientists believe that they have identified at least one gene involved in the development of Stargardt. Defects in the ABCR gene are believed to initiate the series of events that lead to the death of the cone photoreceptors
How common is it?
Stargardt macular dystrophy is the most common form of inherited juvenile macular degeneration. It is estimated that the incidence of Stargardt dystrophy is between 1/1660 and 1/15000 and accounts for seven per cent of all retinal dystrophies.
How is Stargardt macular dystrophy transmitted?
Stargardt macular dystrophy affects males and females alike. It is an inherited disorder of the retina and its mode of transmission is called autosomal recessive. This means that the affected individual has received the disease-causing gene from both parents. The parents, who may not be affected themselves, are called carriers.
If each parent is a carrier of the disease-causing mutation, the chance of having an affected child is one in four with EACH pregnancy.
If I have Stargardt macular dystrophy, will my children have it too?
The risk of a person with Stargardt having an affected child is very small, unless the other partner also carries the recessive gene for the condition. It is possible in families where Stargardt macular dystrophy has occurred to screen individuals to establish whether or not they are carriers of the ABCR gene. However, it is thought that other genes are involved in causing this condition and these tests are still only available in a research environment.
There are some forms of Stargardt macular dystrophy for which the gene has not yet been found, and for which testing is not available, even on a research basis.
How is it diagnosed?
An eye doctor may suspect the diagnosis of Stargardt dystrophy if a young patient has a history of progressive loss of visual acuity that cannot be corrected with prescription eyeglasses.
The following tests are used to confirm the diagnosis of Stargardt macular dystrophy:
- Fluorescein angiography - fluorescein dye is injected into the arm so that specialized photographs of the retina can be taken
- Electro-oculography (EOG) -- electrodes are applied to the eyelids while the patient looks to left and right (this is only performed occasionally when the ERG is not informative - see below)
- Electroretinography (ERG) - the tiny electrical currents generated by the millions of light sensitive cells in the retina in response to standardised flashes of light are measured.
Are there any treatments to slow the vision loss?
There is no scientifically proven treatment for Stargardt macular dystrophy at the present time. It cannot be cured, and there is no known therapy that slows the progress of the disease. However, there are many technological aids available (such as binocular lens and magnifying screens) that can help people minimize some of the problems they face. The patient and low vision specialist should work together to make a choice of the most useful type of lens to aid reading, watching and protecting the eyes.
Nutrition
It is very likely that a diet strong in leafy green vegetables may be protective to the retina. During the winter, if fresh fruits and vegetables are limited, a multivitamin that has vitamins E and C may be useful. These vitamins are thought to act as "anti-oxidants" and protect against light damage in the eye. A diet that includes fish at least twice weekly may also be helpful - as fish contains omega-3 fatty acids, especially docosahexaenoic acid (DHA) which is found in high concentration in the normal retina.
Avoidance of UV Rays
At least one scientific study has shown that mice with Stargardt macular dystrophy raised in darkness have a slower rate of cone degeneration than their counterparts living in regular lighting conditions. This has led some scientists to believe that individuals with Stargardt should ensure that their eyes are protected from harmful UV rays, especially when outdoors over water, or near snow on a bright, sunny day.
Accutane
While one study in an animal model of the human condition did show that Accutane could reduce the number of deposits that are seen in the macula, these studies have not been extended to a clinical trial in humans.
Are there other diseases like Stargardt macular dystrophy?
There is also a look-alike disorder called autosomal dominant Stargardt-like macular dystrophy. As the name implies, this disorder is dominantly inherited. This means that a person need inherit only one copy of the disease-causing gene to become affected. Unlike carriers of the more common, recessively inherited Stargardt, carriers of autosomal dominant Stargardt are always affected. Patients tend to be older when first identified than autosomal recessive Stargardt dystrophy. The gene for the dominant form has been identified. It is called ELOVL4 and is presumed to function in the pathway of synthesis of very long chain polyunsaturated fatty acids.
Related Conditions
Fundus flavimaculatus is a condition which is accepted as being the same as Stargardts, with the same symptoms and manifestations, but is more often associated with later onset and generally has a better prognosis. The main feature of this condition is yellow-white spots and flecks of various shapes, accompanied by minimal changes in the macula.
Are there any research developments?
In 1997, researchers established that autosomal recessive Stargardt macular dystrophy is caused by a defect in the ABCR gene. ABCR is responsible for giving the instructions for the production of a protein involved in the recycling of vitamin A compounds to and from the photoreceptor cells in the retina. The defect in the ABCR gene causes the production of a protein that cannot perform its transport function. As a result, photoreceptor cells degenerate and vision loss occurs.
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 eventual therapies.
Cool Folk with Stargardt Macular Dystrophy
Marla Runyan is an American athlete who competes for gold on both the U.S.A. Olympic and Paralympic teams. Originally a heptathlete, Marla is now a runner of great accomplishment and a role model for everyone interested in sports.
Stephen King is one of the world's best known writers of scary fiction. Not many people know that Mr. King also has vision severely impacted by Stargardt macular dystrophy.
This information has been reviewed by:
Ian M. MacDonald, M.D., FRCSC
Department of Ophthalmology
University of Alberta
Edmonton, Alberta
This information has been provided by The Foundation Fighting Blindness - Canada and has been reviewed by its medical advisor. It is not intended to replace the advice of a qualified vision care professional. The Foundation urges everyone affected by an eye disorder to seek the best healthcare possible.