Myopia and high degree myopia
Myopia, often known as "being short sighted", causes your vision to be blurry in the distance but clearer when looking at things up close. It is a very common condition of the eyes. For most people it can easily be dealt with using contact lenses or glasses, which will make your vision clear and crisp.
How the eye works
Your eyes are shaped like a round ball. At the front of your eye is a clear tissue called the cornea that allows light to enter your eye. Light is focused through your pupil which is a hole in the centre of the iris; the coloured part of your eye. Behind your iris is the lens, which also focuses the light coming through your cornea. Both the cornea and the lens focus the light coming into your eye onto an area of your retina.
The space inside your eye is full of a jelly-like substance called the vitreous. The vitreous is clear and takes up the space between the lens and the retina.
The retina is made up of a number of layers but the most important for vision is the layer made up of cells called photoreceptors. Photoreceptors are cells which are sensitive to light. There are two main types of photoreceptors; one type called cone cells and another called rod cells. Cone cells are found in higher numbers around the central part of your retina, called the macula. Rod cells are found in higher numbers towards the outer edge of your retina.
Underneath the retina is a layer of blood vessels which help to keep the retina healthy.
To the side of your macula is an area called the optic disc. This is where the optic nerve leaves your eye. The optic nerve connects the eye to your brain.
When light enters your eye it is focused first by the cornea and then more accurately by the lens, so that reaches the retina properly. The focussing that your cornea and lens does helps to make your vision clear and sharp. When the light reaches your retina the photoreceptors react to the light reaching them by sending a small electrical charge through your optic nerve to the brain. The photoreceptors react differently to different light levels or lighting conditions and this changes the nature of the electrical signals that are sent through your optic nerve. When the parts of the brain that deal with vision receive these electrical signals they make sense of them and this provides us with the pictures that we call sight. All this happens so quickly it is almost instant.
For vision to be clear, light entering your eye needs to be focused accurately on your retina. Light entering your eye is first focused by the cornea and then fine focused by the lens behind the pupil. This focusing system of your eye makes sure that when light enters your eye it is sharply in focus when it hits the retina. This means that we see everything in focus without any blurriness.
Refractive errors are a group of eye conditions which mean the eye is unable to correctly focus light on to your retina. Refractive errors usually cause your vision to be blurred. Myopia is one of 3 refractive errors. The other types of refractive error are called hypermetropia, or long-sightedness, and astigmatism; you may hear this being described as when the shape of your eye is more like a rugby ball than a spherical shaped football.
Myopia, often known as 'being short sighted' causes your vision to be blurry in the distance but clearer when looking at things up close. It is a very common condition of the eyes and for most people it can easily be dealt with using contact lens or glasses, which will make your vision clear and crisp.
Most people have myopia because their eyeball has grown too long or their cornea (the clear window at the front of the eye) is more steeply curved than usual. These differences cause a problem with the way your eye is able to focus light.
If you have myopia the light coming into your eye from distant objects comes to a focus point before it reaches your retina which makes vision blurry. When you move closer to an object, this changes the focusing of the light and the object is then in focus on the retina and therefore looks clear.
Classification and grading of myopia
It is possible to measure how much myopia you have by doing three things:
- Measuring your eye ball from front to back.
- Measuring how steep your cornea is.
- Testing your vision to see how in focus objects are in the distance.
When you go for an eye test the optometrist (optician) performs some or all of these tests and is able to tell what focusing power your eye has. They can tell if you have myopia from these tests. Optometrists measure the focusing power of your eye using dioptres. This is a technical term for how strong a lens would have to be to give you focused vision. The common way for writing myopia is to say how many dioptres your lens would need to be to correct your sight back to its normal level.
Generally speaking this is written like "-3.00 dioptres (D)". On your glasses or contact lens prescription a minus sign is used to show that the lens you need corrects for myopia. The higher the number the more short sighted you would be:
- Mild myopia includes powers up to -3.00 dioptres (D).
- Moderate myopia, values of -3.00 to -6.00D.
- High myopia is usually myopia over -6.00D.
Most people with myopia are below -6.00D, but some people have much higher levels of myopia. The level of your myopia can be an indicator whether your myopia may lead to further problems with your eyes. Most people with myopia of less than -6.00D don't develop any further problems and the blurriness their myopia causes is easily dealt with by glasses or contact lenses. This is sometimes known as simple myopia. People with myopia higher than -6.00D may be at risk of certain eye conditions that require treatment other than spectacles. This is also known as degenerative or pathological myopia.
Development of myopia
You can develop myopia at any age, however it does have a tendency to develop in childhood or teenage years and it can get worse as you get older. Myopia in young children can get worse as they get older. Myopia can become more stable in adulthood; however there may be episodes where the myopia continues to increase. These episodes can happen at any age and are more common if you have higher levels of myopia. In general the younger you are that myopia begins to develop, the higher the level of myopia you will reach. For some people their myopia reaches a certain level and stays the same for many years.
Causes of myopia
It is not known what causes myopia and research suggests there could be a number of different reasons for it to develop. Myopia does run in families so is thought to be partly genetic. Children who have one parent with myopia have a higher chance of developing myopia. This chance increases if both parents have myopia.
Myopia can also develop because of other conditions you may have. If you have diabetes you may experience temporary myopia when your blood sugar level is not well controlled. Some types of cataracts can cause myopia to develop. Where your myopia is caused by diabetes or cataracts, glasses alone may not be the best way to correct the change in your vision. Good control of your blood sugar levels will help stabilise your vision and your diabetic nurse and GP would be able to help you to achieve this. The myopic changes caused by early cataracts may be corrected by glasses. When cataracts continue to develop this may not be possible and surgery to remove the cataracts would improve your vision.
If you have high myopia (over -6.00D) your eyes may be healthy and with glasses or contact lenses you may have good vision. You tend to have high myopia because your eye has grown in length. This means that even though your eyes are healthy, you are at a higher risk of developing eye conditions and changes associated with the lengthening of the eye.
One eye condition that you may experience is a posterior vitreous detachment (PVD). A PVD occurs because of natural changes to the jelly (the vitreous) in your eye and does not normally threaten your sight. It tends to develop later on in life, but it can develop earlier if you have myopia.
If you have high myopia then there is a higher chance of you developing a retinal detachment. This is where a hole or tear can develop in the retina when it has been stretched. The fluid in the eye can leak through this gap and behind the retina. This can cause your retina to detach from the back of your eye. The symptoms of a PVD and retinal detachment are:
- flashing lights
- a recent onset, increase or change in your floaters
- curtain effect coming down, up or across your vision.
It is important if you notice any of these symptoms or any new symptoms that you have your eyes checked immediately by an eye specialist.
You also have a higher risk of developing glaucoma and you may develop cataracts at an earlier age.
If you have been diagnosed with pathological myopia you have very high myopia and your eye may also show degenerative changes affecting the back of the eye. These changes can cause a reduction in your sight.
The stretching of your retina as your eye grows longer causes it to become thinner. A common change in pathological myopia is areas of retinal atrophy. These are areas where your retina has become very thin and can affect how your retinal cells work. When an optometrist or ophthalmologist looks into your eye the areas of atrophy look very pale and blood vessels that are behind the retina can be seen through them. Your vision at these areas may be reduced or even blanked out causing blind patches in your visual field. Retinal atrophy can occur anywhere on the retina and if it happens in the macula area, it can affect your central vision.
At the edge of your retina there may be retinal changes and thinning that develop known as lattice degeneration. In many people lattice degeneration is regularly monitored by an eye specialist and usually causes no problems. The risk of retinal degeneration increases with the presence of lattice degeneration, which in turn increases with high myopia. Laser treatment or cryotherapy may be needed to these areas to prevent a retinal detachment from developing.
As the eye stretches it can cause breaks to appear on the retina, which look like fine lines. These are known as lacquer cracks and are breaks that occur in Bruch's membrane. Bruch's membrane is found between the retina and the choroid (the retina's blood supply). There isn't any treatment for lacquer cracks and they don't affect your vision directly. However they are the first signs of further problems which can develop and cause changes to your vision.
In some people new blood vessels can grow from the blood supply in the choroid layer, through lacquer cracks or areas of atrophy and onto the retina. This is known as choroidal neovascularisation (CNV). These new blood vessels can bleed very easily as they are very weak and fragile, causing damage and swelling to the retina. If new blood vessels develop at the macula it is known as myopic macular degeneration or myopic maculopathy.
The damage to the retina caused by new blood vessels causes scarring, which will permanently affect your vision. At the macula, this scarring is called a Foster Fuchs spot. This is a circular area of pigment which develops after the new blood vessels and bleeding has gone. Changes to your central vision can make it difficult to read and see people's face. You may also find that your colour vision is affected.
Treatment of myopia
Most people who have myopia may not have any complications and will only need glasses or contact lenses to make their vision sharper. If your prescription is over -10.00D, then you would be entitled to a NHS complex lens voucher to use towards the cost of your glasses or contact lenses. Your optician would be able to tell you how much this voucher is worth and if your prescription would entitle you to a NHS complex lens voucher.
The higher your level of myopia is, the higher the risk of developing eye conditions and the changes associated with myopia. If your retina has been damaged then your vision may need more than glasses to help you see well.
A low vision clinic, which is located in the eye hospital, can be very helpful. Low vision aids, such as magnifiers can help to make things you are looking at bigger. They will be able to provide practical help and advice on how to use your remaining vision. Your eye specialist would be able to refer you to the low vision clinic for an assessment.
There are no treatments available to stop your eye from developing the complications of high or pathological myopia. This is because it is not possible to control the growth of your eye. Currently treatment is aimed at improving your vision and to treat any complications if and when they happen. You will be monitored regularly by your eye specialist who will check the health of your eyes. It is important to have your eyes checked by your eye specialist as soon as possible if you notice and changes to your vision or any new symptoms.
The type of treatment you may need will depend upon the eye condition or the change that has developed. Not all the eye changes that happen in pathological myopia can be treated. There are a number of complications which may occur because of pathological myopia and these include:
Cataracts can take some time to develop before they affect your vision. When your daily activities are being affected by your cataracts, surgery will be considered to remove them.
If you have been diagnosed with glaucoma then you may be prescribed eye drops to help control it. It’s very important that you use your eye drops as advised by your eye specialist as this will prevent you from experiencing any future sight loss due to glaucoma. It’s also important to attend any hospital eye appointments regularly to monitor your glaucoma.
A retinal detachment can be repaired by different types of surgery. If you have a retinal detachment, it’s important that you are seen by an eye specialist as soon as possible. They would be able to assess the detachment and decide which type of surgery would be best for you.
New blood vessels
New blood vessels that may develop can be treated with a type of laser, known as photodynamic therapy (PDT). Before the laser is used they will inject you with a light sensitive drug called Verteporfin. This injection is usually given in your arm. The Verteporfin will travel to your eye through your blood vessels and will fill the new blood vessels that are growing. Your eye specialist will be able to see these new vessels clearly and apply the laser to them. The laser causes a reaction with the drug which seals off any new blood vessels that may be growing. This treatment needs to be given at the early stages of the blood vessel growth so that it can prevent the new blood vessels causing damage.
Recently anti vascular endothelial growth factor (anti-VEGF) medications have been developed to stop new blood vessels from growing. A growth factor is present in the retina which causes the new blood vessels to form and leak. Anti-VEGF drugs work by blocking the effects of the growth factor. The anti-VEGF drugs stop the growth of new blood vessels, thereby reducing the risk of scarring and further sight loss. Unfortunately, at the moment this treatment is not automatically available on the NHS, though your ophthalmologist may be able to arrange funding.
A large proportion of people who have pathological myopia suffer from light sensitivity or photophobia. You may find bright light uncomfortable or you find it difficult to adapt to changing levels of lighting. Using sunglasses, tinted lenses and sunshields can help to reduce the discomfort and glare you may experience in everyday living.
Most people who have myopia find their vision improves when they wear their glasses or contact lenses. However, it’s completely natural to be upset when you are diagnosed with an eye condition associated with myopia. It’s normal to find yourself worrying about the future and how you will manage a change in your vision.
It can sometimes be helpful to talk over some of these feelings with someone outside your circle of friends or family. At RNIB, we can help with our telephone Helpline and our Emotional Support Service. You may also find your GP or social worker can help you find a counsellor if you feel this might help you.
Help to see things better
Having pathological myopia can cause changes to your vision in the long term, but much can be done to help you make the most of your remaining vision and adapt to any changes.
There are lots of things that you can do to make the most of your remaining vision. Making things bigger, using brighter lighting or using colour can all help towards making things easier to see. There is more about this in our leaflet called "Starting out - Making the most of your sight" which is available from our Helpline on 0303 123 9999.
You can also ask your ophthalmologist, optician or GP to refer you to your local low vision service, which can provide you with magnifiers to help with reading and advice on lighting to help you make the most of your sight. Local social services should also be able to offer you information on being safe in your home and getting out and about safely. If you need it, they should also be able to offer you some practical mobility training to give you more confidence when you are out.
Our Helpline can also give you information about low vision clinics and the help available from social services on 0303 123 9999. They can also offer help if you have any difficulties accessing these services. Our website offers lots of practical information about adapting to changes in your vision and products that make everyday tasks easier.
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