Refractive errors like nearsightedness are very common—and very treatable.
Using vision correction, like glasses or contact lenses, is incredibly common in the US. According to the Vision Council, roughly 76% of adult Americans use some kind of vision correction—and by far the most common reason they do is a refractive error.
You’ve almost certainly heard of refractive errors, but you probably know them by another name. Nearsightedness, farsightedness, astigmatism, and presbyopia are the most common refractive errors, and most of us either have one of these conditions ourselves, or know someone who does.
Even so, not everyone is familiar with what these terms describe, or what causes refractive errors in the first place. So let’s get into the specifics—but in order to do that, we’ll first have to talk a little bit about how the eye works.
What is refraction, and what does it have to do with vision?
When we’re talking about eyesight, refraction refers to the way light bends when it moves through different substances. You’ve seen refraction in action when you look through a glass of water, and the images from the other side appear “broken.” The parts you see through the water are shifted a little bit, and the edges don’t match up with the rest of the image. That’s because when the light passes through the water, it comes out at a slightly different angle.
Our eyes bend light too. At the front of our eyes is a clear layer called the lens, which we can control with tiny muscles that change its shape slightly. When we look at something, light passes through the lens, and then through the clear liquid in the middle of the eye—the vitreous humor. Finally, that light lands on the retina, the membrane at the back of the eye that connects to the optic nerve. The retina translates the light into electrical signals, and the optic nerve sends them to the brain to be interpreted into vision.
It’s the job of the lens to bend the light we see so that it all comes together in a sharp, focused point on the retina. When we look at things up close or far away, those tiny muscles adjust the shape of the lens so that the light focuses in the right place. It’s all a very delicate balance—which also means that it doesn’t take much to disrupt.
A tiny change in shape makes all the difference
For people with perfect vision, the lenses keep light focused right where it belongs: on the retina. But what if the retina isn’t exactly where it’s supposed to be?
That’s the case for many people who need corrective lenses. The eyeball itself isn’t a perfect sphere, and it can be stretched out, squeezed, or otherwise slightly out of shape, causing the light’s focal point to land a little bit in front of or behind the retina. Alternatively, the problem can also be with the lens: if it’s too stiff or too flexible, or the muscles that move it aren’t working properly, it can’t focus the light in the right place. When that happens, the result is blurry vision.
Fortunately, our eyes aren’t the only things that can take advantage of refraction. When we make corrective lenses like glasses or contacts, we’re using refraction to bend the light a little bit before it reaches our eye’s lens. That way, once it gets there, the lens can bend it the rest of the way, and even a slightly “imperfect” eye can see crystal clear.
The focal point determines the symptoms
The kind of disruption to your vision that you experience depends on where your eyes focus light. For some people, objects are clearer up close, whereas others might see faraway objects better.
Nearsightedness: The focal point lands in front of your retina. Your eye might be too long, front to back, or your lens too curved. Faraway objects are blurry, but up close, things are clearer.
Farsightedness: The focal point is behind your retina. Front to back, your eye may be too short, or your lens may be too flat. Objects are blurry up close, and clearer far away.
Astigmatism: The focal point is inconsistent, or there are multiple. Your vision might be blurry at any distance.
Presbyopia: Presbyopia can also be called “age-related farsightedness.” As we age, our lenses become less flexible, making it harder to focus on up-close objects—because our lenses can’t bend enough, the focal point lands behind the retina. As with farsightedness, objects are blurry up close, and clearer farther away.
We often think of vision as unchanging, since we rely on it every day. In reality, though, most of us will experience vision changes over the course of our lives. Nearsightedness often shows up in childhood, presbyopia is common as we age, and astigmatism can develop at any time.
Refractive errors can have big impacts
Despite being extremely common, refractive errors still sometimes go undiagnosed. That can happen for a range of reasons: children who don’t realize their vision isn’t normal, or adults whose vision changed so gradually that they haven’t noticed the struggle. In many cases, it just comes down to a lack of access.
But untreated refractive errors can have outsize effects. Kids perform worse in school and sports if they struggle to see the board or their homework. Adults might face a higher risk of falls and injuries, and have a harder time navigating the world independently if they can’t drive.
That’s why regular eye exams are an essential part of healthcare. Together, you and your provider can monitor your vision over time, and take action if and when you notice changes. Vision changes may be normal, but if left untreated, they can still have a significant impact on your quality of life—and a trusted provider can help you figure out your options.