This Science Update answers the question "Why do fevers give you chills?"
The need for reading glasses seems to be an inevitable part of growing older. This Science Update will satisfy your curiosity about why that is.
A close-up look at nearsightedness. I’m Bob Hirshon and this is Science Update.
Science Update listener Andrew Lee of Herndon, Virginia, called our Why Is It line with a question of perception:
"Why do some people have to wear reading glasses?"
We asked Myron Yanoff, chair of the Opthamology Department at MCP Hanneman College in Philadelphia, and he said that losing our near vision is a result of the lens in our eye being unable to focus properly. It often happens because as we age, the lenses become less and less elastic.
"As you, I wouldn't say get older, but become more mature, you lose the ability to focus. And that is a very slow and constant thing, almost from birth on, so that by the time you reach the age forty, you do not have the ability to focus at near."
But he says that people who are nearsighted, and already use glasses to see distant objects, may never need any to see their morning paper.
"All of their friends are putting their glasses on to read and they're taking their glasses off to read."
Doctor Yanoff adds that people who get laser surgery to correct their distance vision may also wind up needing reading glasses. Once their eyes are made normal, they too will suffer age-related loss of near vision.
If you've got a visionary science question, call us at 1-800-WHY-ISIT. If we use it on the show you'll get a free Science Update Mug. For the American Association for the Advancement of Science, I’m Bob Hirshon.
Making Sense of the Research
One consequence of aging is a loss of flexibility and elasticity in various tissues. In most cases, the result is just stiffness, a loss of maneuverability or agility. But in the case of the eye, there can be loss of basic function. As the lens gets less able to change shape and focus light, people must resort to wearing glasses for reading. This increase in far-sightedness is almost universal among older people.
Now try to answer the following questions:
- Why do some people lose near vision?
- Do people lose near vision quickly or does it happen over a period of time?
- What does it mean to be nearsighted? What does it mean to be farsighted?
- If a person gets laser surgery to correct his/her distance vision, could he/she still need glasses at some later date?
For more information about the eye, check out A Big Look at the Eye on the KidsHealth website. This page contains a diagram of the eye as well as text that explains the different parts of the eye. There is also a slide-show presentation of the eye in action (requires Shockwave plug-in).