"In macular dystrophy, a pigment builds up in cells of the macula. Over a period of time, the substance may damage cells that are crucial for clear vision."
Macular dystrophy is a form of rare, genetic eye disorder that causes loss of vision. Macular dystrophy affects the retina in the back of a person's eye. More specifically, it leads to damage of cells in an area in a person's retina called the, 'macula.' The macula is responsible for central vision. When the macula is damaged, people experience difficulty with seeing straight ahead, making it hard to read, drive, or perform other activities of daily living that require fine, central vision.
In macular dystrophy, a pigment builds up in cells of the macula. Over a period of time, the substance may damage cells that are crucial for clear vision. An affected person's vision often times becomes distorted or blurry. Usually, people with macular dystrophy maintain peripheral vision and are not totally blind.
Macular Dystrophy Types
A number of forms of macular dystrophy have been identified by the medical community. These forms of macular dystrophy include the following:
Stargardt's: Stargardt's is the most common type of macular dystrophy and usually occurs in a person's childhood. A different form of Stargardt's called, 'fundus flavimaculatus,' is usually found in adults. Stargardt's is characterized by formation of pigmented waste cells in the person's retina.
North Carolina Macular Dystrophy: North Carolina macular dystrophy is an extremely rare form of the eye disease identified by a very specific genetic marker. Although it is named for North Carolina family members who have this inherited form of macular dystrophy, the disease has been found in other places around the world.
Vitelliform Macular Dystrophy (VTM): VTM is usually first discovered due to the presence of a large, yellow oval lesion in an egg yolk shape that shows up in the center of the person's macula. A number of genetic mutations of this form of macular dystrophy have been identified, to include Best's disease, which affects children and young people. A different version of the disease also may appear in adults, with macular lesions that vary in both shape and size.
Additional types of macular dystrophy may cause specific degeneration of light-sensitive cells known as, 'cones.' The cones are responsible for color vision and are most concentrated in the macular area of a person's retina. While not technically macular dystrophy, 'Retinitis Pigmentosa,' is an inherited photoreceptor dystrophy that destroys light-sensitive cells in a person's eye.
There are essentially two types of macular dystrophy. A form called, 'Best disease,' usually appears in childhood and causes varying degrees of vision loss. The second form affects adults, usually in mid-adulthood and tends to cause vision loss that slowly worsens over time. People with Best disease often have one parent with the condition - the parent passes the gene on to their child. For adult-onset macular dystrophy it is less clear how the condition is passed from parent to child. Many people with adult-onset macular dystrophy do not have other family members with the condition.
Causes of Macular Dystrophy
Macular dystrophy is caused by a genetic mutation. In some people, doctors have identified two specific genes that are affected. Mutations in the BEST1 gene cause Best disease and at times - adult-onset macular dystrophy. Mutations in the PRPH2 gene cause adult-onset macular dystrophy. In most people with macular dystrophy; however, it remains unclear which gene is affected and the exact cause is not known. It is also not known why mutations in these genes leads to the buildup of pigment in a person's macula. Doctors also do not know why only central vision is affected.
Diagnosing Macular Dystrophy
Symptoms of macular dystrophy can include decreased visual acuity with no clear cause, such as refractive errors or cataracts. If your eye doctor suspects you have macular dystrophy, they might order eye tests that are not a part of a regular eye examination in an attempt to reach a definitive diagnosis. For example; a test called, 'flourescein angiography,' can detect retinal damage from macular dystrophy.
A test using optical coherence tomography (OCT) can also be performed to analyze eye tissue for the potential presence of a yellow-brown pigment found in the retinal pigment epithelium (RPE). Lipofuscin is waste material sloughed off from deteriorating eye tissue. Yet another option is an, 'electroretinographic (ERG) test that involves placing an electrode on your eye's outer, clear surface known as your, 'cornea,' to measure how well photoreceptors in your retina respond to light.
Treating Macular Dystrophy
The plain fact is - there is no effective treatment for macular dystrophy at this time. Vision loss usually develops slowly over a period of time. There is ongoing research on macular dystrophy that involves stem cell placement and the potential benefits.
If you have macular dystrophy, you will need to visit a retinal specialist who will assist you with determining the exact nature of the disease. For example; some types are progressive while other types are not. Genetic analysis and counseling might be needed to help you determine the type of macular dystrophy you have and whether the eye condition is likely to be passed on to your children. You may make better decisions concerning family planning if you have an idea of the degree of vision loss associated with the type of macular dystrophy you experience.
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