BEST DISEASE/VITELLIFORM DYSTROPHY
Best disease (also known as vitelliform macular dystrophy) is an inherited form of macular degeneration characterised by a reduction of central vision.
Best disease affects the macula, the central part of the retina responsible for fine visual detail and colour perception. The retina and its component photoreceptor cells are essential to vision as they convert light into electrical impulses and then transfer these impulses to the brain via the optic nerve.
Although the age of onset of Best disease can vary, it is usually diagnosed during childhood or adolescence. In the initial stages, a bright yellow cyst (fluid-filled sac) forms in the retinal pigment epithelium (RPE) beneath the macula. On examination, the cyst looks like a sunny-side-up egg. Despite the presence of the cyst, visual acuity may remain normal or near normal (between 6/9 and 6/18) for many years. Peripheral (side, upper and lower) vision usually remains unaffected.
In many individuals with Best disease, the cyst eventually ruptures. Fluid and yellow deposits from the ruptured cyst spread throughout the macula. At this point the macula has a scrambled egg appearance. Once the cyst ruptures, the macula and the underlying RPE begin to atrophy causing further vision loss. As a result, central vision tends to deteriorate to about 6/36 late in life. However, Best disease does not always affect both eyes equally. Many individuals retain useful central vision in one eye with a visual acuity of about 6/12 in the less affected eye.
In some cases, Best disease does not progress far enough to cause significant central vision loss. However, retinal specialists can still detect the disease using sophicated diagnostic tests that measure the function of the RPE and the retina. Individuals with Best disease are also often farsighted which can be corrected with glasses.
Best disease is genetically passed through families by the autosomal dominant pattern of inheritance.
Click here for Inheritance Pattern.
Currently, there is no treatment for Best disease. Ongoing scientific research is directed at understanding the cause of Best disease. A gene for Best disease has already been mapped (located to a specific region) to a human chromosome. Next, this gene will be identified and its function in the retina determined as the first step in developing means of treatment and prevention.
Individuals with Best disease may benefit from the use of low-vision aids and, possibly, orientation and mobility training.