What is the macula?
The macula is located at the centre area of the retina at the back of the eye. The retina contains cells which are light sensitive and send messages to the brain via the optic nerve. Although very small, the macula is responsible for all of our central vision, most of our colour vision and the finer details of what we see. If the macula is damaged, a person will find it hard to read, drive, watch television or recognise faces.
In some dystrophies the cells of the macula gradually die (atrophy). In others, tiny abnormal blood vessels grow into the macula. They are fragile so can leak and scar the macula. The medical term for this is choroidal neovascularization (CNV). In the more common age-related macular degeneration (AMD), similar symptoms are sometimes referred to as ‘dry’ and ‘wet’ macular degeneration respectively.
What are the symptoms?
A person with Juvenile Macular Dystrophy will gradually lose part or all of their central vision. They will dislike bright lights, have problems identifying colours, or in the early stages, find their night vision inferior than before. Children may find it difficult to see and read the whiteboard at school. Some may see dark spots at the center of their vision, or see straight lines as curved.
Macular dystrophies are caused by a faulty gene from one or both parents.
Dominant forms – these are caused by a faulty gene from one parent. The parent with the faulty gene will have the condition themselves and there is a 50:50 chance that they will pass the gene on to their child.
Recessive forms – these need a faulty gene from each parent. The parents probably won’t have the condition themselves, although they both carry the faulty gene.
How is juvenile macular dystrophy diagnosed?
Most patients are diagnosed after visiting an optician after noticing a problem. The optician will refer the person to an ophthalmologist (specialist eye doctor) who is a genetic specialist at a hospital. Further tests to determine the specific dystrophy the person has might include:
Visual Field Testing:
Visual field testing accesses the full range and sensitivity of a person's vision, horizontally and vertically, detecting blind spots (scotomas) which could be a sign of eye disease. The many tests available aren’t painful or invasive.
The most common type of visual field test is often seen at opticians. The patient sits with their chin on a rest and a patch over one eye. There is a button which they are asked to press when they see one or more flashing lights. This process maps the patient's visual field, and can point to areas of the retina where there is vision loss.
A dye called fluorescein is injected into the bloodstream via the patient’s arm. This travels to the eye and highlights blood vessels in the retina. A photograph is taken of the back of the eye.
ERG measures electrical signals produced by the retina following flashes of light. The test uses electrodes placed on the cheek under each eye. The patient looks at black and white checks moving across a TV screen and a lamp flashes light into the eye three times per second.
The electrical responses are viewed and recorded on a monitor. Abnormal patterns of light response suggest the presence of macular disease.
Optical coherence tomography (OCT)
OCT is a scanning device that works a little like ultrasound. Ultrasound captures images by bouncing sound waves off living tissues; OCT does it with light waves. The patient places his or her head on a chin rest and an invisible, near-infrared light is focused on the retina. Cross-sectional pictures of the retina are analysed for any abnormalities which could indicate retinal degeneration. OCT is sometimes combined with infrared scanning laser ophthalmoscopy (ISLO) to provide additional surface images of the retina.
A genetic test usually involves having a blood sample taken. DNA is extracted from blood cells and analysed in the laboratory. The analysis involves looking very carefully at the genetic code to try and identify the genetic alteration that is causing the condition. Many people have the genetic cause identified, although it’s not always possible.
What are the main types of juvenile macular dystrophy?
Stargardt disease (fundus flavimaculatus)
This recessive genetic condition is caused by an alteration in a single gene cell. It is the most common form of juvenile macular dystrophy, also known as fundus flavimaculatus.
The disease causes an area of the retina to waste, which eventually leads to the area being surrounded by a ring of white or yellow spots. An accumulation of ‘waste’ material called lipofuscin also affects an important area of the retina called the retinal pigment epithelium (RPE).
Usually diagnosed in people under the age of twenty when they first notice their vision getting worse and Stargardt disease is in the early stages. People may have good visual acuity, but have difficulty reading or seeing in dim light. Other common symptoms of Stargardt disease include blurriness and distortion of vision.
It is thought that people with Stargardt disease cannot process vitamin A properly so it is important to avoid excess vitamin A. Also avoid bright light as it may accelerate the progress of the disease.
Best disease is also known as early-onset vitelliform macular dystrophy, and is a dominant form. In its early stages, pictures of the retina can look like an egg yolk. Later they look like scrambled egg. There is also an accumulation of lipofuscin (a waste material).
It usually appears in childhood, but the onset of symptoms and the severity of vision loss vary widely. The adult-onset form of Best disease begins later, usually in mid-adulthood, and tends to cause vision loss that worsens slowly over time. The two forms of Best disease each have characteristic changes in the macula that can be detected during an eye examination.
The abnormal accumulation of lipofuscin can cause damage to cells that are critical for clear central vision over time. People with this disorder often lose their central vision, and their eyesight may become blurry or distorted as a result. It does not affect side (peripheral) vision or the ability to see at night.
Sorsby fundus dystrophy
This is a very rare form of JMD. It normally develops during the person's 20s or 30s, usually in both eyes. Sorsby dystrophy is inherited from a dominant gene and can be diagnosed with a genetic test. Often a person with Sorsby dystrophy also develops CNV. They may have a sudden distortion or loss of vision. If this happens, it’s vital to get urgent medical attention at a hospital eye unit, as the sight loss may be slowed if treated quickly.
This is another dominant form, sometimes confused with AMD. This usually develops later in life, with people displaying different patterns of damage in each eye, which may change over time. Most people keep good vision in at least one eye.
Bull’s eye maculopathy
This describes a number of different conditions in which there is a ring of pale-looking damage around a darker area of the macula. The macula can often appear to have circular bands of different shades of pink and orange. Age of onset and severity of sight loss varies, and it can be inherited in many ways.
Doyne honeycomb dystrophy
This is a dominant condition. Small spots called drusen appear which gradually form a honeycomb pattern of damage to the retina. Typically, people with this condition do not have symptoms until they are aged between 30 and 40 years old. Early visual symptoms may include decreased visual acuity, problems seeing colour, eye discomfort in bright light and distorted vision.
There are various ways in which cone dystrophy is inherited but it is most commonly described as ‘sporadic’ (no recognised pattern of inheritance). People with the condition tend to be light-sensitive and have problems distinguishing colours from the early stages of the disease. People who develop the disease early may also experience rapid involuntary eye movements called nystagmus. Central vision may become affected later.
The symptoms of cone dystrophy vary from one person to another, even among individuals with the same form of the disorder. The age of onset, specific symptoms, severity, and progression (if any) can vary greatly.
Pseudoxanthoma elasticum or ‘PXE’ is a disease affecting many parts of the body. Fibres in the skin, eyes and blood vessels lose their elasticity. When this happens behind the eye, the retina can stretch and become brittle, causing cracks. Blood vessels grow through the cracks and leak, causing scarring of the macula. If you experience sudden distortion or loss of vision, get urgent attention at an eye hospital. Treatment might stop the blood vessels growing.
There are no known treatments for most dystrophies yet. However, if you develop CNV (abnormal blood vessels) you may be able to have injections to stop their growth and preserve the sight you have left. If you experience any sudden changes in vision, seek urgent medical advice from an eye hospital.
What can I do to look after my eyes?
Visit your optician at least every two years for a general eye test.
- Don’t smoke.
- Maintain a healthy weight and blood pressure.
- Wear lenses which block UV and blue light, particularly in bright sunlight. Blue block filters also reduce glare.
- Wear a hat with a wide brim or visor to shade eyes from direct sunlight.
- Limit alcohol intake to recommended levels.
- Eat lots of fruit and green, leafy vegetables.
Low vision aids, lighting and technology
A number of tools and devices can help people with Juvenile Macular Dystrophy carry out daily activities and maintain their independence. Low Vision Aids can be helpful for many daily tasks and range from simple Magnifying Glasses with Lights to Electronic and Video Magnifiers.