Myopia, or the need for corrected vision to focus or see objects at a distance, has become a lot more common in recent decades. Some even consider myopia, also known as nearsightedness, an epidemic.

Optometry researchers estimate that about half of the global population will need corrective lenses to offset myopia by 2050 if current rates continue–up from 23% in 2000 and less than 10% in some countries.

The associated health care costs are huge. In the United States alone, spending on corrective lenses, eye tests and related expenses may be as high as US$7.2 billion a year.

What explains the rapid growth in myopia?

I'm a vision scientist who has studied visual perception and perceptual defects. To answer that question, first let's examine what causes myopia–and what reduces it.

How myopia develops

While having two myopic parents does mean you're more likely to be nearsighted, there's no single myopia gene. That means the causes of myopia are more behavioral than genetic.

Optometrists have learned a great deal about the progression of myopia by studying visual development in infant chickens. They do so by putting little helmets on baby chickens. Lenses on the face of the helmet cover the chicks' eyes and are adjusted to affect how much they see.

Just like in humans, if visual input is distorted, a chick's eyes grow too large, resulting in myopia. And it's progressive. Blur leads to eye growth, which causes more blur, which makes the eye grow even larger, and so on.