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Refractive errors

Refractive errors include myopia (short-sightedness), and hyperopia (long-sightedness) with or without astigmatism (when the eye can sharply image a straight line lying only in one meridian).

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. This focusing system of your eye makes sure that when light enters your eye it is sharply in focus as it hits the retina. This means that we see everything in focus without any blurriness.

Causes of Myopia

Myopia, (short sightedness), 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 lenses or glasses, which will make your vision clear and crisp.

People with myopia have an eye which bends the light coming into it too much. In other words, the light comes to a focus point before it reaches your retina. This makes vision blurry and is caused by the eyeball being too long or the cornea (the clear window at the front of the eye) being more steeply curved. When you move closer to an object, this changes the focus of the light and the object is then in focus on the retina. Therefore it looks clear.

You can develop myopia at any age, however it tends to develop in childhood or teenage years and it can get worse as you 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 myopia reaches a certain level and stays the same for many years.

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. 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.

Some types of cataracts can also cause myopia to develop. The myopic changes caused by early cataracts can be corrected by glasses. When cataracts continue to develop this may not be possible and surgery to remove the cataracts would improve your vision.

High myopia

You tend to have high myopia (over -6.00D) when your eyes have 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 and stretching of the retina.

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 eyes and it does not normally threaten your sight. It tends to develop later 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 your retina when it has been stretched. The fluid in your eye can leak through this gap and behind your retina. This can cause your retina to detach from the back of your eye.

Symptoms of posterior vitreous detachment

·        Flashing lights

·        A recent onset increase or change in your floaters

·        A 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 (raised eye pressure) and as a result, may develop cataracts (clouding of the lens) at an earlier age.

Treatment of myopia

Most people who have myopia don’t have any complications and will only ever need glasses or contact lenses to make their vision sharper. Your optician would be able to determine the kind of glasses or contact lenses you’ll require.

Recent studies have confirmed the existence of a large burden of uncorrected refractive errors, although the interventions required are significantly cost effective, and have an important impact on economic development and quality of life. Severe refractive errors have been estimated to account for about 5 million blind people. According to the most recent data available to WHO, there are an estimated 124 million people in the world with low vision. About a fourth of these would benefit from low vision services.

Source:

RNIB

IAPB

WHO​