Joel Hunter, MD Refractive Surgeon, Hunter Vision Updated 04/10/19 10:05 AM
When it comes to vision, some people are born lucky. If you’re reading this because you must put on a pair of glasses to read, you are one of those people. It means you made it through the entirety of elementary, middle, and high school with good vision. You never bore the shameful burden of having to show up to school one day with your dumb new glasses. A third of us weren’t so lucky. For us, our genetics said, “Hey, it looks like this is a uniquely awkward time of life, you know? Really filled with social uncertainty and anxiety. How ’bout some nerdy glasses to give your self-esteem a boost?” And then our chromosomes slapped telomere high-fives and laughed. Getting glasses in middle school is hard. But because the arc of the universe bends towards justice, those unlucky nearsighted kids would one day become those who, in triumph, can read a menu without glasses.
Why does an early need for glasses age-proof you against needing glasses to read later in life? The reason is directly related to where your eye naturally focuses. When you’re young and nearsighted (a.k.a. myopic), your eye has clear vision—called its “focal point”—at some useless, unhelpful distance like four feet or four inches depending on how myopic you are. The reason I say “unhelpful” is because even Butch Jockman with his varsity jacket and eagle vision can see up close clearly as well.
There’s a key feature of the lens inside our eye: its autofocus only works in one direction. It can dial up focusing power to see better up close, but there is no opposite ability to push focus out into the distance. Another way to say this is that for the unfortunate, glasses-wearing myope, the focal point can never be pushed out any further out than that useless four feet or four inches.
So, Chelsea Cheercaptain can see everything clearly from the adoring fans in the top row of the bleachers to the pompoms in her hands without glasses. Her focal point is set perfectly way out in the distance, so the lens in her eye can effortlessly autofocus on anything closer.
What about the poor nearsighted guy in the band who forgot his glasses? He can read the music on that weird tiny music stand on his trombone, but the lens in his eye can’t do a dang thing to focus on anything beyond that. This fact about the lens in our eyes—that it can only increase focus for near, but never for distance—means some people are born lucky. They can see clearly in the distance, and all the near vision is easy too. But if you’re reading this, you already know it doesn’t last forever.
The reason is that even if you’re born lucky, it’s an immutable fact of aging that your luck will eventually run out. The lens inside your eye adds new layers each year, and it gets denser as a result. It becomes less flexible. And with decreasing flexibility, the autofocus devolves from easy, to difficult, to impossible. The distance vision stays pretty good because the focal point was set out there in high school and it remains there to this day.
So how do you add the focusing power necessary to bring that focal point close enough to read your phone? The answer is a pair of reading glasses, which you’ll notice have a “+” sign in front of the number to signify how much power they add. As a kid, you probably walked past the drugstore rack of reading glasses a thousand times without ever noticing them. Now those same glasses can help you with a problem you never had back in those days.
The additional focusing power in reading glasses usually ranges from +1.25 through +3.50, and most people will try on a few different pairs to see which number works best. But you know who still walks right past that rack of readers without a thought? That guy who played trombone a couple paragraphs back. His useless, unhelpful focal point set at arm’s length has finally become useful after all.