Explainer:Why myopia gets worse over time
Here are the reasons your myopia gets worse:
Poor vision habits
- Too much close work,
- while wearing glasses that are too powerful (see Differentials and Lens-induced myopia),
The actual mechanism is an area of active research, but the general result is axial elongation. The eye grows longer, requiring stronger correction, in a cycle.
Other bad habits which affect vision, though probably don't contribute to progression of myopia:
- Not blinking enough, causing Dry eye
- Animated explanation
Myopia, also known as shortsightedness is not a disorder, a disease, or a lifetime sentence to expensive glasses slash contacts. It's actually your eyes doing their job properly. Our eyesight is an amazing dance between the software of our brains and the mechanisms of our eyeballs. It's a series of tiny unconscious adjustments made in response to the stimulus of looking at something.
If your glasses prescription has been getting stronger over the years, that's often the result of a feedback loop of stronger lens correction and your eyeballs compensating to deal with it. Thankfully, changes in eyesight are not a one way street. Let's talk about how your ability to see things clearly at a distance can get slowly better over time instead of worse.
First, the basics of eyeball mechanics. At some point, you probably learned what lenses do. Lenses change the direction of rays of light Positive lenses bend light towards a single point. Negative lenses spread that light out. Positive and negative lenses working together can adjust where that point of focus falls.
Your eyeballs contain a flexible positive lens. This lens is framed by a ring of muscle called the ciliary muscle. When the ciliary muscles relaxed, your lens is at its thinnest. When the ciliary muscle contracts, it pushes inward causing your lens to bulge more. This basically happens without your conscious control. Amazing. Your eyeball has one almighty directive from the brain. Focus the light from the object you're looking at onto your retina at the back of your eyeball. When it hits perfectly, you get a clear image. If it falls short or long of the retina, you'll experience blurriness. The amount of work Your eyes have to do depends on how far away the object is. If you experience myopia, you know that things in the distance are more blurry than things that are nearer to your face.
Let's compare the task of focusing at different distances to the task of hand picking apples from a tree. You want to be able to reach the maximum number of apples and you have two mechanisms with which to accomplish this, your arm and the ladder. Your arm is like your ciliary muscle, it can move quickly to make slight adjustments, and zero in on the apple of your choice. The ladder in this metaphor is the length of your eyeball. The ladder determines the larger range within which your arm can work. How do you choose the right ladder height for apple picking? The best ladder is the one that positions your arm to reach the most apples. Now I want you to imagine the apples towards the top of the tree or your close up eyesight tasks. Things like reading, computer and phone use, sewing, drawing, etc. The apples towards the bottom of the tree are the things that require distance vision, like playing sports, driving, and generally navigating the outdoors. Let's say that the apples at the top seemed like the best to you, you're really going after those, your arm is getting tired of stretching most of the time though, so you adjust your ladder to be taller. And now you can comfortably work in that top Apple range. But you can only reach down so far, and there's no way you'll get those bottom apples unless your ladder gets shorter, or unless you step down on the ladder. It's not a perfect metaphor, but now you know how your ciliary muscle and the length of your eyeball work together.
Let's take this back to the realm of eyesight, you're having trouble seeing things far away. Your eye doctor gives you glasses. You can see far away now fabulous. Then you go home and read for a few hours with your new glasses on. While you're doing that your ciliary muscle is working extra hard to cancel out the strong new negative lens that's making this close up image, the book, fall behind your retina.
If you do something like this every day for months and years, your ciliary muscle is going to get so overworked that your eyeball will grow a tiny bit in length to give it a break. But now, your glasses don't seem to be working quite as well as they used to. And you can't see as far as the distance anymore. So you go to the eye doctor, they prescribe you some stronger lenses, and the cycle continues. In the next video, we'll look at ways to break this cycle and introduce habits that can restore your distance vision over time.