Why do people become short sighted?

17 May 2020

Short-sightedness, also called myopia, is the eye condition that causes distant objects to appear blurred, while close objects can be seen clearly. This usually occurs because the eyes grow longer than that of someone that can see well at distance. Approximately 1 in every 6 British adults is myopic (17.8% of the population).

Typically, the onset of short-sightedness occurs in school age around the 6 to 14 years of age and progresses over time during the teenage years when the body grows rapidly and the eyes exert more hours of near work.  It usually stabilises in the early years of adulthood.

The degree and severity of short-sightedness varies between people and can range from mild to high myopia where a person’s vision is significantly affected.

Causes of short-sightedness

The exact causes why people become short sighted are not fully clear yet but our understanding of the cause of myopia has improved significantly over past years with hundreds of scientific studies.

It has been suggested that both genetic and environmental factors play a role in the development of short-sightedness.

The rates of myopia prevalence vary amongst different ethnic and geographic populations, with East Asian populations having the highest incidence.

Some studies have also demonstrated that the risk of a child being myopic increases with the number of myopic parents. This means that the chances of developing myopia when one of the parents is short-sighted doubles compared to those children whose none of the parents are myopic; and increases by almost eight times when both parents are myopic.

While it is very likely that genetic factors have an effect on myopia development, the increase in prevalence over the years has suggested that environmental factors such as the amount of near work and outdoors activities must also play a role.

How our eyes react

When we look at objects close up, our eyes need to adjust and focus the near object whose image should be formed at the back of the eye (retina) in order for us to see it clearly. Sometimes our eyes do not quite meet the focus demand required and so we generate a blurred image behind the retina.

When this happens, the clever reaction of the body is to try to get that image focused by elongating the eye so the image can no longer be blurry. However, this happens to be counterproductive generating a progression on the degree of short-sightedness.

In turn, activities such as near work, close distance reading and continuous reading are strongly associated with myopia development. Consequently, there are studies that showed that individuals with 10 years or more of education could be expected to have 0.60 mm longer eyes.

The importance of time outdoors

Outdoor activity has been associated with lower levels of myopia progression. It is believed that looking at a distant target for 2 to 3 hours could neutralize the effect of 9 to 12 hours doing near work.

Similarly, it has been demonstrated that exposure to natural sunlight stimulates the release of dopamine from the retina, which inhibits eye growth and the subsequent progression of myopia.

How many are short-sighted?

In the United Kingdom, myopia was found to affect 2% of children between 6-7 years old and 15% of 12-13 year olds. It has been observed that as the prevalence of myopia increases, the onset happens at an earlier age and therefore allows more time for the degree of myopia to progress into high myopia.

Can we avoid short-sightedness?

Several methods have been trialled to slow myopia progression and some of them have shown effective results. Speak to your eye care practitioner if you are interested to know more.

Some of the things you can start doing to avoid myopia progression are having regular breaks when doing close-up work, by looking at distant objects and spending time outdoors.

Also, if you are short sighted it is particularly important to have regular eye tests at least every two years or at any point if you have concerns about your vision.

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