What are the causes of short-sightedness (myopia)?

The exact cause of short-sightedness is not completely understood, but several factors contribute to this refractive error, which is characterised by clear eyesight up close but blurry distance vision.

Short-sightedness, or myopia, occurs when an eyeball grows too long or the cornea becomes too steeply curved. The result is that light entering the eye doesn't come to a clear focus point on the retina, which is required for clear vision.

Researchers who study myopia have identified at least two key risk factors.

The first is genetics. More than 150 myopia-prone genes have been identified in recent years. One such gene alone may not cause the condition, but people who carry several of these genes have a much higher risk of becoming short-sighted.

Myopia — along with these genetic markers — can be passed along from one generation to the next. When one or both parents are short-sighted, there’s a greater chance that their children will develop myopia.

The other major risk factor for myoopia is focusing the eyes up close for extended periods of time, such as when reading or staring at the screens of computers, tablets and smartphones. 

As myopia causes a person's distance vision to become blurry, squinting is a hallmark sign that a person is becoming short-sighted. Squinting reduces the size of the opening through which light enters the eye. This creates a "pinhole camera effect" which makes distant objects look a little clearer.

Unfortunately, frequent squinting leads to another common symptom of myopia: headaches.

Early detection of myopia is important. If discovered early, myopia control measures can be started to slow the progression of short-sightedness. This is important because high levels of myopia can increase the risk of developing serious eye problems later in life, such as glaucoma and retinal detachment.

Even if you don't know exactly what causes it, myopia is easily detected during a routine eye examination by an optometrist. To reduce your child's risk of high myopia later in life, schedule an eye test at the beginning of the school year with an optometrist near you.

Find Eye Doctor

Find an optometrist near you

Find Eye Doctor