Macular degeneration is most common in elderly people. However, there is also what is known as ‘juvenile macular degeneration’ (JMD), which is a blanket term for a number of different hereditary eye diseases. These diseases include juvenile retinoschisis, Best disease and Stargardt’s disease. JMD affects both children and young adults and, while rare, it can lead to full loss of central vision.
Unfortunately, no cure currently exists for any of these diseases, as they are caused by genetic mutations. Rather, young people who suffer from it will be provided with adaptive training, visual aids and other forms of assistance that enable them to lead a normal, active life in spite of it. Scientists also continue to look into causes, treatment and prevention of JMD.
Oftentimes, genetic counseling is also offered to families that are known to have the genetic mutation, or whose children have been diagnosed with JMD. If people know that they have the mutation, counseling will help them to determine what the risk of actually passing them on are. Additionally, it will help them in terms of coping strategies for living with a child with visual disabilities.
JMD causes damage to the macula, which is the tissue that is found right in the center of the retina, positioned at the eye’s back. The macula is responsible for making sure our central vision is clear and sharp, enabling us to drive, read and recognize faces, as well as allowing us to see colors clearly.
Let’s take a closer look at the three main diseases that cause JMD.
This is the most common type of JMD. It gets its name from Karl Stargardt, the German ophthalmologist who first discovered it in 1901. This disease affects around one in every 10,000 children in this country. The condition usually manifests before the age of 20, but most will not experience any vision loss until they are between 30 and 40 years of age.
The condition is often diagnosed when yellow spots start to appear on the macula. The spots, which are known as fundus flavimaulatus, appear all over the back of the eye. They are deposits of fat that cells create, but that the body can’t deal with.
Most people start to notice that they have Stargardt when they develop black or gray spots in their central vision and find it increasingly difficult to read. Both eyes are affected and will gradually lose their central vision. Once the vision is measure at 20/40, progression increases until it reaches 20/200. This is the rate at which someone is classed as ‘legally blind’. Some people reach this stage in just a few months, while others take decades.
Peripheral vision, which is the vision at the side, is not lost. Similarly, most people with Stargardt do not become night blind. However, they do often find it more difficult to adjust when light changes. When the disease reaches later stages, it is often difficult to see color.
It is believed that Stargardt is caused by a specific gene. If both of the parents carry one normal gene and one mutated gene, the chance of developing Stargardt is 25%. If only one mutated gene is inherited, then they don’t develop the disease. They can, however, pass it on to their own children.
No cure exists, but significant benefits have been experienced through ACT (Advanced Cell Technology). Stem cell treatment has received FDA orphan drug designation as well, as it has been found to help in the protection and regeneration of photoreceptors, found in the retina. This can slow down the progression of Stargardt.
To date, stem cells have only been used in animal (rat) test subjects. A 100% improvement was noted compared to rats that did not receive treatment, and no negative side effects were seen. Additionally, it showed that the photoreceptors in the animals were rescued, which prevented them from going blind. It is hoped that the same results will be seen in human test subjects as well.
Since 2012, clinical trials have started to take place on human test subjects. Results are not available yet. So far, it seems that the retina in patients with JMD have clumps of vitamin A. These clumps are called ‘vitamin A dimers’. Other studies have taken part looking specifically at these dimers, although these to date have only been performed on mice. However, researchers are very positive about the results to date.
As a result of these studies, the National Eye Institute has granted a $1.25 million grant to see what the link is between retinal degeneration and vitamin A. Depending on the results of these studies, new approaches to treatment may be developed.
A second possible cause of JMD is known as ‘Best disease’, also known as Best vitelliform macular dystrophy. This condition was discovered by Friedrich Best, another German ophthalmologist, in 1905. This disease most often becomes apparent between the ages of 3 and 15. However, some people develop it much later.
People who have Best disease develop sacs filled with a bright yellow fluid. These cysts form underneath the eye’s macula and they are often described as looking like eggs. Most patients have normal to near normal vision when the cysts begin to form. However, the sac will burst, causing the fluid to spread in the macula itself. In children, one pupil will often appear red, whereas the other is white.
The disease takes a number of years to progress, going through various stages. At first, no loss of vision occurs. However, later on, central vision starts to get lost, usually in both eyes although some only experience it in one eye. At this point, vision becomes distorted and blurred. In the later stages, central vision can deteriorate even further, eventually reaching 20/100. However, some people can go through life with Best disease without ever experiencing the later stages or even having any vision loss. Others go blind very quickly in one eye, but have no effects in the other.
If one parent carries the Best disease gene, there is a 50% chance that their child will develop it, even if the other parent does not have the defective gene. If a child does not develop Best disease, it means he or she does not have the gene. As such, the gene will not be passed on to future generations either.
Juvenile retinoschisis is the final condition that can cause JMD. It is also known as X-linked retinoschisis. It usually only happens in young males, as it is related to the X chromosome (the male chromosome). Usually, between the ages of 10 and 20, they start to experience vision loss. It then remains stable until they reach the age of between 50 and 60.
People with juvenile retinoschisis have a retina that splits into two distinctive layers within the macula itself. The space between these layers is then filled with blood vessels and blisters. The blood vessels are unstable, which means they start to leak blood that mixes with the vitreous fluid. Vitreous fluid is the clear, gelatin liquid that the inside of the eye is filled with. After some time, the vitreous fluid becomes compromised and pulls away from the retina, and some people also experience full retinal detachment, where it actually comes away from the eye’s wall.
The clearest symptom of this condition is loss of central vision, which tends to range from 20/60 to 20/120. Additionally, patients tend to struggle to focus on a single object using both eyes, something that is known as strabismus. They may also experience nystagmus, which is an involuntary eye movement. Around 50% of those who have juvenile retinoschisis will lose their peripheral vision as well. As previously stated, vision often stabilizes until patients are between 50 and 60 years old, after which it deteriorates very quickly to reach 20/200.
The X chromosome is believed to carry the defective gene that leads to juvenile retinoschisis. Women also carry this gene, and there is a 50% chance that they will pass the gene to their daughter. However, the daughter would then become a carrier, rather than actually developing the condition herself. Rather, she will then have a 50% chance of passing it on to her children and if this child is a son, he will get the disease. Men, on the other hand, can only pass the gene on to a daughter. The daughter will not develop the condition, but will simply become a carrier.
There is no treatment for juvenile retinoschisis. However, if the retina detaches, surgery can often alleviate the symptoms.
Resources and References:
What Is Juvenile Macular Degeneration? – Information on juvenile maculopathy. (American Academy of Ophthalmology)
Stargardt’s Disease (Fundus Flavimaculatus) – Information on Stargart’s disease. (All About Vision)
Juvenile Macular Degeneration – Information on juvenile macular degeneration. (WebRN)
Stargardt Disease Defined – Information on Stargardt’s disease. (American Macular Degeneration Foundation)
Facts About Stargardt Disease – Information about Stargardt’s disease. (National Eye Institute.