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Stargardt's Macular Dystrophy
is an inherited eye condition which affects the central area of the retina called the macula.
Which part of the eye does Stargardt's affect:
Stargardt's disease mainly affects the macula area of the retina. The macula is found at the centre of the retina where the incoming rays of light are focused. The macula is very important and is responsible for:
1. what we see straight in front of us
2. The vision needed for detailed activities such as reading and writing, and
3. Our ability to appreciate colour.
Stargardt's disease is sometimes called a Juvenile Macular Dystrophy since it tends to first appear between the ages of 10 to 20. Stargardt's causes some of the cells on the macula to stop working leading to problems with central vision, detailed vision and sometimes with colour perception.
What causes Stargardt's:
It had been recognised for a long time that Stargardt's seemed to run in families, so it was always thought that Stargardt's was an inherited condition. Just recently one of the genes responsible for Stargardt's has been discovered. It would therefore appear that Stargardt's is a genetic condition. Genetic conditions are usually caused by 'faulty' versions of genes.
What is a ‘faulty' gene:
We each inherit two sets of genes, one from our mother the other from our father. These sets of genes 'lie' in pairs and they determine the many things which make us individuals; such as hair or eye colour. There are two ways a condition can be passed through genes to children (two classifications of inheritance). These are called dominant inheritance traits and recessive inheritance traits. What is the difference between dominant and recessive traits: It is important to remember when discussing the inheritance traits that genes lie in sets of pairs, one set from each parent. A dominant trait is inherited from only one of our parents. With this type of inheritance only one copy of the 'faulty' gene is needed. When it lies in its pair with the gene from our other parent it is the dominant one and ‘switches on' the trait. It is 'dominant' over the other gene inherited from the other parent and the child will have the condition. With recessive traits two faulty copies of the gene are needed so both parents have to carry the faulty copy. When this happens the trait will be ‘switched on'. If a normal copy of the gene is inherited from one parent then the 'normal' copy of the gene will override the 'faulty' copy and the child will not have the condition. If both parents pass the faulty gene on to the child then the child will have the condition.
How does Stargardt's fit into these patterns:
Stargardt's has an autosomal recessive pattern of inheritance in 90 percent of cases. When two people who have the faulty Stargardt's gene have a child then that child may have Stargardt's Macular Dystrophy. Usually people who have the Stargardt's gene do not have the disease since the 'normal' copy of the gene from their other parent has switched off the 'faulty' gene. This means that Stargardt's often occurs in families that have no history of the disease in the past. However it is highly unlikely that someone with Stargardt's will pass on the disease unless their partner has Stargardt's or is a carrier of the 'faulty' gene
Which gene is faulty in Stargardt's:
Until recently the faulty gene which caused Stargardt's remained undiscovered but in 1997 a group of scientists published a paper describing the gene responsible for Stargardt's macular dystrophy. At the moment this has not yet led to any new treatments but developments in gene therapy are occurring all the time.
How Stargardt's affects the eye:
There are two main findings on the retina of individuals with Stargardt's disease. First an oval lesion often referred too as ‘beaten bronze' in appearance around the macular area. This lesion tends to deteriorate over time and causes changes in the way the cells of the macular are able to work. This leads to a loss of visual acuity, meaning people's vision becomes less clear. The second change are yellowish flecks which surround this lesion. Sometimes people have just these flecks without the macular lesion. These people used to be diagnosed with Fundus Flavimaculatus. However, some researchers believe that these two problems, the macular lesion and the yellow flecks, are both caused by the gene which causes Stargardt's and therefore are different expressions of the same genetic problem. It has also been suggested that Fundus Flavimaculatus and Stargardt's do vary in age of onset and severity where Fundus Flavimaculatus may appear in their 20's and 30's and vision may be more severely affected.
How Stargardt's affects vision:
Stargardt's main effect is on the macula. The macular is a small area on the retina. This area has a concentration of cone cells. Cone cells are responsible for sharp and central vision, because of this Stargardt's main affect is on central vision. Central vision is used when we are looking straight ahead or doing anything which needs detailed vision such as reading, sewing or computer work. At first Stargardt's will make this vision unclear and then sometimes distorted or blurred. People who have had Stargardt's for a while may have a blank patch in the centre of their vision which doesn't move wherever they focus. Stargardt's does not affect other parts of the retina so does not normally affect peripheral or side vision. Since we use our peripheral vision when we are moving around most people with Stargardt's can manage to keep getting out and about on their own. Stargardt's can also cause people problems such as glare and difficulties adapting to changing light conditions.
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