Best Disease

Best disease (also known as vitelliform macular dystrophy) is an inherited form of macular degeneration characterised by a reduction in central vision.  The disease begins in childhood and affects the central part of the retina (known as the macula) which is responsible for fine visual detail and colour perception.  The progression of visual loss varies between those affected by Best disease but side or peripheral vision generally remains unaffected.

Early signs of Best Disease usually develop between the ages of three and 15.  During the early stages the disease doesn’t always have much effect on vision so the child may not notice any issues with their sight.  It is often picked up at a routine eye examination before it has chance to affect the vision.

The disease is increasingly being picked up through screening programmes.  This allows family members of a patient who has Best disease to have a genetic test to identify if they may develop the condition.

Sometimes a child may notice a change in their vision with the resulting eye test confirming they have retinal changes which could indicate Best disease.  Although a child may notice early vision problems they may not develop vision problems until later on in life – generally over the age of 40 or 50.

The Five Stages of Best Disease

There are five stages to Best disease.  None of these stages can cause pain and can be identified by a doctor when observing the retina in the back of the eye.

Stage One

During this stage the macula appears healthy and no change can be seen on examination.  There is generally no effect on vision however there may be subtle changes to the layer below the macula.

Stage Two

This stage is known as the ‘vitelliform stage’.  At this stage a blister appears on your macula area which looks like the yolk of an egg.  Although this changes can be seen by a doctor, there is no or very slight change to vision.  This stage generally appears between the ages of three and 15.

Stage Three

This stage is known as the ‘pseudohypopyon stage’.  During this stage some of the yellow matter that causes the blister can breakthrough a layer beneath your retina.  This leads to the formation of a cyst under the retina.  Again during this stage there may be little change to your eyesight.  This stage generally occurs in the teenage years.

Stage Four

This stage is known as the ‘vitelliruptive stage’.  During this stage, lesions begin to break up and can cause damage to some of the cells in the layers of your retina.  At this stage you may start to experience changes in your vision.  Straight lines may begin to appear wavy or you may encounter difficulties in reading small print.

Stage Five

The final stage of Best disease is known as the ‘atrophic stage’.  The yellow material which caused the legions to form begins to withdraw and disappear leaving behind scarring and damaged cells on your retina.  At this stage your sight is more seriously affected and you may have difficulty in reading.

These are the classic stages of Best disease however some people develop another stage, known as ‘choroidal neovascularisation’.  This stage develops during the final stage when the eye begins to try and fix the damage to the macula by creating new blood vessels.  Unfortunately these new blood vessels can lead to further damage and cause further difficulties with vision.

Best disease can be present for a long time without experiencing any difficulties with your sight.  It is not until stage four or five that your sight is normally affected.  These stages generally do not occur until you are over the age of 40, however in some cases it may appear in someone’s late twenties or early thirties.

Symptoms

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 also experience problems when 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 middle. Straight lines can appear distorted and wonky or as if there is a little bump in them. These changes may be experienced in only one eye.

You must arrange to see an optician if:

  • Your vision isn’t as clear as it used to be
  • Straight lines no longer appear straight
  • You experience difficulty reading small print

Diagnosis, Screening and Tests

If an ophthalmologist believes that you may have Best disease they will thoroughly examine your retina.

Your vision will be checked and your pupils dilated to allow the ophthalmologist to observe the macula. The drops used to dilate your pupils generally take around 30 minutes to work. These drops will cause your vision to become blurry and heighten your sensitivity to light. The drops are necessary to allow your ophthalmologist to see the insides of your eyes more easily. The effects of the drops normally pass in about six hours however sometimes it can happen overnight. It is not safe or advisable to drive until the effects of the drops have fully disappeared.

A special lamp called a slit lamp is used to inspect the inside of your eye. Your ophthalmologist will ask you to look in various directions while shining a light directly into your eye (although bright, this light will not cause any damage to your eye). This will allow them to identify any changes that Best may have caused.

It is not always possible to identify if you have Best disease using this examination alone. Further tests may be needed to find out for certain if you have Best disease including:

Fluorescein angiogram

This test allows your ophthalmologist to find out more about your Best disease. Although a slit lamp allows your ophthalmologist to see the damage to your retina it does not allow them to view the network of blood vessels beneath it. A fluorescein angiogram allows them to photograph these blood vessels and see if any changes have occurred that may be causing problems.

In order for the pictures to display properly, a yellow dye is injected into your arm which travels through your blood stream to your eye. The injection is not painful but can make some people feel nauseous. The dye allows the blood cells to become visible when a picture is taken. After the dye has been injected you will be asked to look at a special machine. The machine will photograph the back of your eye as the dye travels through the blood vessels. The test usually takes around 10 minutes and you will experience a series of flashing lights as the pictures are taken.

It is a very common test and does not have any serious side effects to the majority of people. The injection may give your skin a slight yellow complexion from the dye however this passes into your urine (which also may appear a darker yellow than normal).

Optical Coherence Tomography

Optical Coherence Tomography allows photos to be taken of the back of your eye which provide your ophthalmologist with cross- sectional images of the retina, similar to a 3D image of the inside of your eye. No dye is required for this test. Often optical coherence tomography and fluorescein angiogram are used simultaneously to obtain a thorough picture of the retina.

Electroretinography

Electroretinography is a test used by ophthalmologists to assess how the retinal rod and cone cells are functioning. During this test you are asked to look at a screen which displays patterns of lights including flashes and checkerboard patterns. During this time you are normally comfortable sitting upright or lying down. Your pupils are dilated with eye drops and anaesthetic drops will also be put into your eye to numb them. A small electrode is then placed on or near to the front of your eyes. This is similar to placing a contact lens in your eye. The electrode then measures your retinas response to the light patterns. Another electrode is placed on the skin near to your eyes.

The test does not cause any pain. There is however a very rare possibility that that the electrode placed on the cornea may graze it and cause an abrasion. If your eyes feel uncomfortable or painful over the days following the test it is important to contact your local hospital immediately. Corneal abrasions are easy to treat when caught early.

Electro-oculogram

The electro-oculogram test measures how your retina responds to light and eye movement in response to light. This test can be carried out with or without your pupils being dilated. If your pupils are dilated then the test may take longer. If you have a heightened sensitivity to light and are concerned about dilation during the test, please discuss this with your hospital in advance. Electrode pads are placed on the skin near to the nose side of your eye and on the hairline side of your eye. The electrodes will not be placed on or in your eye.

During the test you will be asked to look at different lights when they appear. This often means that you are looking back and forth between illuminated targets. These lights will alternate back and forth at different speeds whilst your eyes follow them. Parts of the test will be performed with the overhead room lights on, and some of the tests will be performed with them off.

There are no risks involved in this test. Some people find that their eyes become tired during the test and may become itchy afterwards, these feelings will quickly wear off.

Treatments

Unfortunately, there is currently no treatment for Best disease.  In 1998, genetic research identified the BEST1 gene as being the cause of the disease.  Researchers are now working on understanding the function of this gene in the retina.  Findings from recent studies have provided clear steps to developing a therapy that could help to prevent sight loss.  Using this new approach, researchers engineer small, safe viruses to deliver the correct version of the BEST1 gene to the retina.

Prevention

Lifestyle choices and diet can play a contributing role in helping to manage Best disease. Certain nutrients such as lutein, zeaxanthin, vinpocetine, l-lysine, a number of vitamins and enzymes, and fish oil may help slow down Best’s disease and preserve vision.

Daily juicing of vegetables and fruits (preferably organic) may also be beneficial.

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