This Is What Really Causes Nearsightedness

Some people have no problem reading a digital clock from all the way across a room, while others need glasses or contact lenses to be able to read the same clock from more than three inches away. It certainly isn't fair, but it is a reality that nearsighted people have learned to live with. There aren't only a few nearsighted people, either. In fact, more than 40% of Americans are nearsighted, and this percentage is only increasing each year, according to the National Eye Institute.

Being nearsighted is far from fun. Many nearsighted people struggle with blurry vision, the need to squint in order to see clearly, and headaches due to eyestrain, says the Mayo Clinic.

Some people are more prone to nearsightedness due to genetics, but that is far from the only risk factor. According to the World Health Organization, people are more likely to become nearsighted if they spend a lot of time indoors or perform many activities (such as reading or watching television) from a short distance.

According to the National Eye Institute, most nearsighted people have abnormally long eyeballs. Because of this, images are focused in front of the retina (the layer of tissue that senses light) instead of on the retina. This causes a person to see well from up close, but poorly from a distance.

The Mayo Clinic notes that people can also become nearsighted if their cornea has too steep of a curve. The cornea is the outer layer of the eye that helps your eye focus light. When the cornea has a smooth curve, it will send any incoming light directly onto the retina, resulting in a well-focused image. If the curve is too steep, on the other hand, the light will only be sent in front of the retina, creating a blurry image for objects that aren't close enough to the person's eyes.

Farsighted people have the opposite problem, with abnormally short eyeballs or corneas with not enough curvature, says Mayo Clinic.