Stargardt's disease constitutes a group of retinal disorders that are inherited in nature. As part of the patho-physiologic process, the retinal cells that are situated in the inner most aspect of retina undergoes progressive degeneration or deterioration in the region of macula, the most sensitive part of retina associated with central vision. All the patients who have well- developed Stargardt's disease have difficulty in maintaining central vision; while peripheral vision remains unaffected. In most cases, the loss of vision is progressive (unless any intervention is taken) and may lead to complete blindness by adulthood.
What Is Stargardt's Disease?
Stargardt's disease is caused by mutations in the ABCA4 gene. Rarely this condition can be also caused by ELOVL4 gene mutations. In the retina ABCA4 and ELOVL4 provide instructions for the optimal production of proteins within the matrix of photoreceptor cells. The primary function of ABCA4 protein is to transports energy and other substance in and out of photoreceptor cells. Mutations or changes in the ABCA4 gene produce a dysfunctional protein that prevents the process of transporting the energy and other toxic byproducts from and to the photoreceptor cells. These leads to the toxic build-up of chemicals and other hazardous substances along with accumulation of lipid rich waste called lipofuscin in the retina that eventually leads to irreparable damage to retinal cells. The advanced and progressive cell death in the retina can lead to gradual vision loss which is the characteristic feature of Stargardt's disease. ELOVL4 also plays a significant role in the production of long chain fatty acids. Exact function of this fatty acid in the retina is unknown. But change in this gene leads to the development of a protein that can affect the normal function of retinal cells ultimately leads to death of the cells causing visual loss.
Incidence in General Population
Stargardt's disease is also referred to as Stargardt's macular dystrophy (SMD) or fundus flavimaculatus in more sophisticated scientific terms. It is considered as one of the most common causes of macular degeneration at a younger age (in most cases clinical manifestation may appear in childhood). It is a fairly common condition and the risk of inheritance of defected gene is 1 in 10,000 in general population.
Research and statistical studies suggest that over 5% of the entire population carries the abnormal gene that is responsible for processing of Vitamin A. This also indicates that 5% of the entire population is susceptible to develop retinal diseases like retinitis pigmentosa and Stargardt's disease.
Most common cause of Stargardt's disease is genetical inheritance. It is usually transmitted to the offspring if parents carry defected genes that control the metabolism of Vitamin A inside the retinal cells. In vast majority of the cases, parents almost never show any signs of visual impairment. Chances are exceptionally high if both parents carry the defected genes.
Sign and Symptoms
Most cases of Stargardt's disease can be identified by characteristic signs and symptoms. This includes:
- Changes in the quality of central vision marked by blurring and distortion
- Unable to see in dim light
- Difficulty in recognizing familiar faces
- Loss of vision acuity that may range from 20/50 to 20/200
- Appearance of small and yellowish blind spots in the central field of vision
- Stargardt's disease may result is complete loss of vision in advanced stages of disease process. In addition, patient may also report changes in the color perception and depth of vision
Vision loss from Stargardt's disease generally begins in early childhood. In most of the cases, it commences at an age as early as 10 to 12 years (with some sort of vision loss by age 20 in over 90% cases). However, it is too difficult to identify the exact time of retinal damage as well as its rate of progression, because variations can occur even among family members with similar inherited tendencies.
Diagnosis of Stargardt's Disease
Diagnosis of Stargardt's disease is usually made on the basis of detection of deteriorating tissue within the retina that may be slough- off from outer covering of retina. These may be noticed as small and yellowish spots. Research suggests that the primary pathology is development of Vitamin A dimers that are basically deposits of Vitamin A in the retinal cells (due to abnormal metabolic pathway). These deposits are also found in age- related macular degeneration.
Treatments and Preventions for Stargardt's Disease
A number of research studies indicate that Stargardt's disease is very strongly associated with the retinal damage that is caused by high intensity sun-rays or ultra violet radiations. It has also been observed that preventing sun-exposure and exposure to light of high wave-length can prevent the development of Stargardt's disease. This can be accomplished by using protective eye-wear or sunglasses that blocks UV radiations from invading deeper layers of eye.
If you have developed Stargardt's disease or you carry mutations that are responsible for Vitamin A metabolism, your doctor may prescribe you specially-designed eye-wear that have the ability to block hazardous wave-lengths of light. A number of research studies are underway that are helpful in reducing the risk of retinal cell damage by stem cell transplantation.
How to Cope with Stargardt's Disease?
According to American Macular Degeneration Foundation it is advisable to provide genetic counseling to all the patients who are at the risk of developing Stargardt's diseases due to inheritance of defected genes or the one who have a positive family history of Stargardt's disease.
As vision loss often appears in younger age, low vision counseling from the doctor is essential to make sure that classroom learning is not hampered. Alterative measures like using large print books and special devices that magnify print can also be used accordingly. Stargardt's disease should be identified earlier to prevent the further complication.