What causes short-sightedness (myopia)?

The exact cause of myopia is not fully understood. However, the mechanics of the eye that cause blurry distance vision are well known. It's what causes small variations in these mechanics that researchers are still exploring. Experts do know that environment and genetics are two important factors.

People with myopia (short-sightedness) have blurry distance vision but clearer eyesight up close. This is mostly because their eyes grew a little too long from front to back during childhood. 

It can also be that their corneas became too steeply curved or, in rare cases, that the cornea and lens are too close to each other. 

Each of these tiny variations can cause light entering the eye to focus in front of the retina, light needs to focus directly on the retina for clear vision at all distances.

Fortunately, experts have found a number of factors that contribute to the onset and progression of myopia.

Genetics

Researchers have identified more than 200 refractive error or myopia-prone genes. Short-sightedness can pass from one generation to the next along with these genes. 

If one parent has myopia, the chances are three times greater that their children will develop myopia. If both parents have myopia, the chances are six times greater.

Time spent outdoors

Spending enough time outdoors is one of the most important lifestyle factors in myopia development. This is because it is often the most easily adjustable factor for many families. 

Research has linked spending more time outdoors in natural daylight with:

• Reduced risk for myopia development

• Reduced progression of myopia to higher levels

READ MORE: Is myopia more genetic or environmental?

Vision habits

Certain vision habits can also cause or influence myopia, the most significant of these habits is focusing up close for consistent, extended periods of time. 

This includes: 

• Reading

• Using a computer

• Looking at a smartphone or tablet

Myopia progression usually stabilises during early adulthood but the habits children and adolescents establish before then can make it worse.

To reduce a child's risk of developing myopia and potentially slow the progression of existing myopia, parents should: 

• Encourage more time outdoors in natural sunlight

• Encourage regular breaks during focused near work

SEE RELATED: Is your child at risk for myopia?

Early detection

Detection of myopia in early childhood is very important. Some children who develop myopia at a young age can go on to develop progressive myopia, which can reach severe short-sightedness, or high myopia. 

High myopia can lead to serious eye problems later in life, including: 

• Glaucoma

• Posterior subcapsular cataracts

• Myopic macular degeneration

• Retinal detachment

But if myopia is detected early enough, myopia control strategies can slow myopia progression during its peak years.

Not all children with nearsightedness will have obvious symptoms. So it's extra important that all children have eye exams at 6 months and 3 years old, and every 2 years throughout school. 

Ask your child's optometrist about lifestyle factors and other available myopia control strategies.

READ MORE: Why myopia progression is a concern — and what you can do about it

Adam Debrowski also contributed to this article. 

Page published on Tuesday, 17 March 2020

Page updated on Friday, 11 August 2023

Medically reviewed on Thursday, 3 March 2022