Myopia, frequently called nearsightedness, can be as inconvenient as it is common. A vision condition that causes nearby objects to appear clear but distant ones to appear blurry, myopia can happen suddenly but often develops gradually. In either case, those experiencing it have to learn to adapt to the loss of clear vision - usually by investing in contact lenses or prescription eyeglasses. 

Such treatments are more sought after than ever as 4 out of 10 people in the world are already nearsighted, with that number expected to rise to 5 in 10 by 2050. It's an increase that concerns the American Academy of Ophthalmology enough to define myopia as an epidemic. Because nearsightedness is so common and concerning, it can be helpful to understand what causes or contributes to it. 

What causes nearsightedness?

The first thing to understand is that no one factor alone always causes the condition. "The most common causes of nearsightedness include a mix of factors," explains Inna Lazar, OD, a Connecticut-based optometrist and founder of Greenwich Eye Care. A significant one is genetics, as research has found more than 200 genes linked to the condition. 

"Anyone can be nearsighted, but you’re at higher risk if you have family members who are nearsighted too," notes the National Eye Institute at the National Institutes of Health. Though the exact degree genetics play isn't known, it's generally understood that "children with no myopic parents have a 1 in 4 chance of being nearsighted, children with 1 parent have a 1 in 3 chance and child with both parents have 1 in 2 chance," explains Laura Di Meglio, OD, an instructor of ophthalmology at the Wilmer Ophthalmological Institute at Johns Hopkins University School of Medicine.

Environmental factors play a measurable role as well. Lazar cites "extensive close-up activities" as one such possible cause. Research shows that this is likely due to frequent eyestrain related to viewing small digital screens, which, over time, causes one's eyeballs to elongate. This elongation is what nearsightedness is. 

Decreased time spent outdoors also affects nearsightedness as outdoor light plays a role in healthy eye development, notes Lazar. She says this is especially common in children. "It's important to remember that the younger a child is when they become myopic, the more likely their condition is to progress," she explains. "This is because myopia in children indicates that the eye is growing too long, causing light rays to focus in front of the retina instead of directly on it."

Is it more common to be farsighted or nearsighted?

While both nearsightedness and farsightedness (called hyperopia) affect millions of people, nearsightedness is more common than farsightedness. Farsightedness affects between 5% and 10% of the population, per the National Eye Institute, while nearsightedness affects about 40% of the population. 

Neither condition is permanently reversible, though some people turn to various laser eye surgeries as a long-term strategy - sometimes with mixed results. "Myopia is a chronic condition, says Di Meglio. "Usually, it starts at a young age and worsens over time. It tends to stabilize in late adolescence, but commonly further progresses in people who continue to do a lot of close-up activities."

How do you treat nearsightedness?

Though nearsightedness can't be permanently reversed, it can be slowed down. Specialized contact lenses, eye drops, and vision therapy can all help; as can lifestyle adaptations such as increasing time spent outside, limiting screen exposure, and by following the AmericanAcademy of Ophthalmology's 20-20-20 rule. This recommendation is to simply take regular breaks from close-up activities by focusing on an object at least 20 feet away, every 20 minutes, for a duration of 20 seconds. 

Nearsightedness also has many treatment options available. Surgery may be recommended; so may orthokeratology - often referred to as ortho-k. "Ortho-k consists of wearing custom-designed lenses overnight," explains Lazar. "They temporarily correct vision by reshaping the cornea and have shown effectiveness in slowing myopia progression."

The most common treatment recommendation for nearsightedness, however, is to wear corrective lenses. Prescription contacts or eyeglasses treat nearsightedness by counteracting the increased curve of the cornea, which sharpens one's vision. With more types of care available than ever before, Lazar says she's grateful to be able to help patients many different ways. "As an eyecare professional practicing in this era, I feel very fortunate."

More:Myopia affects 4 in 10 people and may soon affect 5 in 10. Here's what it is and how to treat it.