Reading in the Dark

Reading in the Dark Photo Credit: Clipart.com

Moms the world over are convinced that reading in low light will wreck your eyes. But are they right? In this Science Update, science reporter Bob Hirshon enlightens us.


Today's Why Is It? question comes from one of Science Update's own writers, Kandice Carter. She wants to know if reading a book in a dim room can really hurt your eyes.

We asked Howard Howland, a vision expert at Cornell University.

Yes, I think there's a chance that you will become more nearsighted if you read in low light.

That's because in low light, your pupil has to open up wider to let in enough light to see. That changes where light normally hits the retina, blurring the image. So the eye gets a signal to grow longer, so the image will hit the right place on the retina. And that can eventually cause nearsightedness.

The larger the pupil, the greater the blur, and the greater the blur, the stronger the signal is for the eye to grow longer, and hence, become more nearsighted.

Howland adds that damage is more likely to occur in young people, where eyes are still developing.

If you've got a science question, we won't leave you in the dark. Call us at 1-800-WHY-ISIT or visit our website, www.scienceupdate.com, and e-mail us. Either way, if we use your question on the air, 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

Nearsightedness, or myopia, is a very common condition that affects between 30 and 40 percent of the U.S. population. It normally first occurs in school-age children. Since the eye continues to grow during childhood, nearsightedness generally develops before age 20.

Myopia provides an interesting context in which to examine the scientific world view because though it is a very common condition, it is a topic about which there is still some scientific debate. A large body of scientific evidence supports the theory that myopia is hereditary. There is also evidence that nearsightedness may be caused by the stress of too much close vision work. The Science Update you just heard explored the possible link between nearsightedness and reading in low light.

Now try to answer the following questions:

  1. What happens to the pupil in low light? Why?
  2. How does the expansion of the pupil potentially contribute to nearsightedness?
  3. When is the onset of nearsightedness most likely to occur? Why?
  4. What type of study would have to be conducted to test the theory of the link between reading in low light and nearsightedness? What controls would you have to put in place? Could you actually perform this study? Why or why not?
  5. What are some other possible explanations for nearsightedness?

For Educators

To further explore the topics of myopia and vision, go to Eye Conditions, Disorders, and Treatments from the Canadian Ophthalmological Society.

An Eye on Color from the Tech Museum of Innovation contains a brief description of the human eye and how it perceives color.

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