Vox - Why so many people need glasses now
Rates of myopia or near-sightedness or needing glasses to see things far away have been rising for decades.
In the US just 25% of people were myopic in 1971. By 2004, that number was up to 42%. And if current trends continue it’s estimated that half of the world’s population will be myopic by 2050. For decades, researchers thought that whether or not you needed glasses was just a matter of genetics. And it partly is. The abruptness of this increase suggests that that this change is environmental.
Most people are born with eyes that are too short from front to back. In this shape, the lens focuses images behind the retina. That makes the eye hyperopic or farsighted. Blurry up close and clear from far away. But as we grow up, our eyes grow too until they reach a spherical shape. In this shape, the lens focuses light directly onto the retina and produces a clear image. But sometimes the eye keeps growing longer. In this shape, the lens can focus up close images onto the retina. So all of us with myopia just have eyeballs that have grown too long. It is a lifelong disease so once you’re myopic, it doesn’t regress.
The evidence points to the way we spend time in childhood and adolescence. That’s when our eyes grow fastest, up until about our early 20s.
Two factors in particular have the biggest influence:
- Near work or the time that we spend looking at things up close.
- How much time we spend indoors.
Some experts theorize that if your eyes grow up straining to look at things up close a lot of the time, they’ll just grow longer to reduce that strain. But the evidence on this explanation is mixed. The stronger explanation is time spent indoors:
- Exposure to bright outdoor light stimulates the production of dopamine in the retina.
- This neurotransmitter regulates eye growth and without enough dopamine the eye doesn’t know when to stop growing and indoors it’s hard to get enough.
The light from the sun has up to a 100,000 lux on a sunny day. Whereas in the room the light levels generally and only about 200 to 300 lux.
We’re born with a finite amount of tissue that make up the various coats of your eyeball. Excessive elongation of that quite simply places additional stress on those structures. The retina has been stretched so much that starts to break and then sort of peel off like an old piece of paint. The longer those eye structures are stretched the higher the risk of disorderslike myopic macular degeneration, retinal detachment, glaucoma and cataracts. So we’re finding this almost linear relationship between them. The amount of myopia and the risks to your vision later in life. We used to think about myopia as an optical defect. Now we think about it much more as a disease.
For those who start to develop myopia there’s treatment:
- Multifocal, soft contacts, and glasses
- They make peripheral vision intentionally blurry which appears to slow the progression of myopia.
- Orthokeratology or ortho-k lenses
- Hard contact lenses worn only at night that reshape the wearer’s cornea while they sleep so that they can see at a distance during the day.
- Atropine eye drops
- Low doses of a substance that temporarily paralyzes the eyes’ focusing muscles which seems to reduce the development of myopia.
- The simplest and most effective way to prevent myopia is to get kids to spend more time outside.