RNIB, supporting people with sightloss
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Eye condition fact sheet: Best disease
Best disease (vitelliform macular degeneration)
Best disease is a genetic condition you are born with although it does usually start to affect your vision until later in life. Best disease affects the macula which is part of your retina at the back of your eye which you use when reading, writing or watching TV. There is no current treatment for Best disease although research is on-going in the area of gene therapy which may lead to a treatment in the future.
Best disease is an eye condition that affects a tiny part of the retina at the back of your eye, which is called the macula. Best disease can start to cause changes at the back of the eye between the ages of 3 to 15 although it does not usually affect vision until later on in life.
Best causes problems with your central vision, but does not lead to total loss of sight and is not painful. Best affects the vision you use when you're looking directly at something, for example when you're reading, looking at photos or watching television. Best may make this central vision distorted or blurry and, over a period of time, it may cause a blank patch in the centre of your vision. Best will not usually affect your peripheral (side) vision.
Best Disease, also called Juvenile Best Macular Degeneration, Juvenile Best Disease and Vitelliform Macular Degeneration, is an inherited eye condition which can affect both men and women. It usually occurs in both eyes (binocular) but it may not affect vision to the same extent in each eye. Sometimes it only affects one eye (monocular).
Best disease only affects the eyes so is not caused by, or linked to, a problem or disease in any other part of the body.
The sight loss caused by Best disease can take many years to develop and some people with Best disease can continue to read into their forties, fifties or well beyond.
Adult- onset macular vitelliform dystrophy is a slightly different eye condition to Best disease. In adult-onset macular vitelliform dystrophy there are less changes at the back of the eye, the changes begin much later in life and they do not progress in the same way. Adult-onset macular vitelliform dystrophy does not usually affect sight until around the age of 40 to 60 with very mild or moderate changes in vision. The change to vision can be so small that often it is detected by chance through a routine eye test. In general adult-onset macular vitelliform dystrophy has less impact on vision than Best Disease. This leaflet is about Best Disease and not Adult-onset macular vitelliform dystrophy.
Effects on vision
The symptoms of Best disease vary from person to person, but usually the first problems people notice are with their ability to see detail. You may have problems reading small print, or you may find that there is a slight smudge in your sight or that your vision has a small blurred area in the centre. Straight lines may look distorted or wavy or as if there's a little bump in them. People may only notice these changes in one eye.
You should have your eyes tested by an optometrist (optician) if:
· you notice any difficulty with reading small print (with your reading glasses if you wear them )
· straight lines start to look wavy or distorted
· your vision isn't as clear as it used to be.
The optometrist will be able to measure any changes in your vision and examine the back of your eye. If they detect any changes to your macula or any cause for concern they will arrange an appointment with the ophthalmologist (hospital eye consultant) for further tests.
The macula
Best affects the macula area of the retina. The macula is a tiny area of your retina which is very important for seeing detail, colour and things directly in front of you.
When the light enters your eye it is focused onto your retina at the back of your eye. The retina includes a number of layers but the most important for vision is a layer made up of cells called photoreceptors. Photoreceptors are cells which are sensitive to light.
The macula, which is a few milimetres in diameter, is a specialised area of the retina that contains a few million photoreceptor cells called cone cells. The macula functions best in bright light levels and allows you to see fine detail for activities such as reading, writing and recognising colours. Best causes your macula to stop working as well as it should.
Away from the central macula is the peripheral retina, composed mostly of the other type of photoreceptor called rod cells. They enable us to see when light is dim and provide peripheral (side) vision outside of the main line of sight.
Peripheral vision is the sight you have out of the corner of your eye when looking straight ahead. Best disease does not affect other parts of the retina so does not normally affect peripheral or side vision. Since we use our peripheral vision when we are moving around most people with Best can manage to keep getting out and about on their own. For example, someone with Best may well be able to get to the local bus stop and see a bus coming but find it difficult to see the number on the bus.
Detecting Best disease
Early signs of Best disease usually develop between the ages of 3 to 15. In these early stages Best disease doesn’t always have much effect on vision so a child may not notice a sight problem. Sometimes it is picked up at a routine eye examination before it affects vision. This is because an optician or ophthalmologist can see changes in the retina at the back of the eye before vision is affected.
Best disease is increasingly being picked up through screening programmes. This means that the family members of someone who has Best disease can have a genetic test to find out if they might develop the condition.
Sometimes a child may notice a change in their vision and an eye test then confirms they have retinal changes which could indicate Best disease. However, even though someone may have changes to their retina because of Best disease at an early age they may not develop vision problems until much later in life - often over the age of 40 or 50.
The five stages of Best disease
There are five stages to Best disease. These stages can be seen by the doctor when they look at the retina at the back of your eye. None of these stages cause eye pain.
Stage 1. At this stage your macula looks healthy and no change can be seen on examination. There may be subtle changes to a layer underneath the macula but there is generally no effect on vision.
Stage 2. This stage is called the vitteliform stage. At this stage there is a blister on your macula area which looks similar to an egg yolk. Although the doctor can see these changes often there is no effect on vision or very slight changes to vision at this time. Usually this stage occurs between the ages of 3 and 15 years of age
Stage 3. This stage is called the pseudohypopynon stage. With this stage some of the yellow matter which causes the egg yolk- like blister can breakthrough a layer under your retina. This leads to a cyst forming under the retina. Again there may be little change in level of sight. This stage is usually seen in the teenage years.
Stage 4. This stage is called the vitelliruptive stage. In this stage the lesion begins to break up and can cause damage to some of the cells in the layers of your retina. At this point you may start to experience changes in your vision. You may start to notice that straight lines look wavy or have problems with reading small print.
Stage 5. This stage is the final stage of Best disease. It is called the atrophic stage. The yellow material which caused the lesions begins to withdraw and disappear. However it leaves behind scarring and damaged cells on your retina. At this stage your sight is more seriously affected and you may find reading difficult.
These are the classic stages of Best disease however some people develop another stage, called choroidal neovascularisation (CNV). This stage develops during the atrophic stage when the eye starts to try to fix the damage to the macula by creating new blood vessels. Unfortunately these blood vessels can lead to more damage and cause further difficulties with vision. However, CNV does not occur in the majority of cases.
You can have Best for a long time without having any sight difficulties. Your sight is not normally affected until stage 4 or 5 which may not develop until over the age of 40, although it can occur earlier in someone's late twenties or early thirties. It isn't possible to know exactly when or how much your sight will be affected as it can vary from person to person.
However not everyone with Best has the same kind of disease progression or sight problems. Some people will not progress beyond the early stages of the disease. Many people will have good vision until they reach their fifties and some people will retain reading vision in one eye throughout life. Vision loss is usually extremely slow in people before the age of forty.
Causes
Best disease is a genetic condition. This means that it is caused by a ‘faulty’ gene which may be inherited from a parent or occur as a new genetic variation. It may be inherited as an autosomal dominant trait. Recently the gene responsible for Best disease has been found but as yet this has not led to any treatment it has shown, however, that people who have the same fault in this gene can have very different symptoms at different ages even within the same family. Best disease can be caused by a faulty gene in chromosome 11 (region 11q12-q13) which is also known as VMD2.
What is a 'faulty' gene?
All genes come in pairs and you inherit one of each pair from your mother and one of each pair from your father. Your genes determine the many things which make you an individual such as hair or eye colour. There are a number of ways a genetic condition can be passed through genes to individuals. But, they all have to start somewhere in the family tree.
These ‘ways’ are also known as modes of inheritance. Best disease is passed on through dominant inheritance.
Dominant inheritance
Dominant inheritance means that a disease is inherited from only one of our parents. When the 'faulty' gene lies in its pair with the gene from our other parent it is the dominant one and ‘switches on’ the trait or condition. It is 'dominant' over the other ‘normal’ gene inherited from the other parent. When someone who carries the Best gene has a child with someone who does not carry the Best gene there is a 50% chance that it will be passed to a child. If a child does not inherit the Best gene they cannot pass it on to their children.
Best disease is not always passed on directly. For more information on genetic conditions talk to your specialist about obtaining a referral to a genetic counsellor at the hospital and your GP about the genetic services in your area. The Genetic Interest Group can also provide you with support and information and their address is at the end of the fact sheet.
Diagnosis
If an ophthalmologist suspects you have Best they will initially thoroughly examine your retina.
Your vision will be checked and your pupils dilated to allow the ophthalmologist to look at the macula. Your pupils are dilated with drops that take about 30 minutes to work. They will make you sensitive to light and cause your vision to be blurry. The drops allow the ophthalmologist to see the inside of your eye more easily. The effects of the drops usually wear off in about six hours though sometimes it can happen overnight. It is not safe to drive until the affects have worn off.
The ophthalmologist looks at the inside of your eye using a special microscope called a slit lamp. You place your chin on a rest and the ophthalmologist sits opposite you. The ophthalmologist will ask you to look in particular directions while shining a light into your eye. This allows them to see your retina and any changes that Best may have caused. Although very bright, the light cannot damage your eye.
Sometimes the ophthalmologist can tell you whether they think you have Bests or not from this examination. However, you may need further tests to find out for certain if you have Best. Further tests may include the following:
Fluorescein angiogram
This test helps the ophthalmologist find out more about your Best disease. The ophthalmologist can usually see the damage to your retina under a slit lamp but they can't see the network of blood vessels underneath it. A fluorescein angiogram is a way of taking pictures of these blood vessels which allows the ophthalmologist to see if there are any changes which could be causing problems.
Before a series of pictures is taken, a yellow dye is injected into your arm which then travels through your bloodstream to your eye. This usually isn't painful but can make some people feel sick. This dye makes the blood vessels visible on the pictures taken.
Once the dye has been injected you will be asked to look at a special machine. The machine takes pictures of the back of your eye as the dye is travelling through the blood vessels. You'll experience a series of flashing lights as the pictures are taken, but the test isn't painful. It usually takes about 10 minutes.