Does reading in the dark hurt your eyes?

- asks Bill from New York

Does reading in the dark really cause damage to your eyesight? [Credit: Mr.Branchphoto.com]
By | Posted October 3, 2007
Posted in: Ever Wondered?, Health
Tags: , ,

When I was in second grade, I locked myself in the bathroom and read Beverly Cleary’s “Dear Mr. Henshaw” from back to front. The rush of it was enough that I started trying to fit longer and longer books into a single day and often found myself as a literate outlaw, reading after hours in a dark bedroom. Today, I wear corrective lenses, and I sometimes wonder how much Nancy Drew and the Hardy Boys are to blame.

Not much, as it turns out. Doctors have been trying for ages to debunk a myth that reading in dim lighting causes permanent damage to your eyes. But a debate lingers among some scientists who say that myopia (or nearsightedness) may be partially caused by environmental factors during childhood.

When the eye adjusts to lower levels of light, many reversible things happen. Muscles around the iris relax and allow the pupil to dilate so that more light will enter and hit the back of the eye. This rear area is where photoreceptor cells called rods and cones turn the light into meaningful information for the brain. As the light lowers, rods and cones enhance their ability to transform the light. These and other adaptive responses kick in once you’ve been sitting in the dark for a few hours, but return to normal in the light.

However, reading or focusing on close objects in the dark can put strain on the eyes. In dim lighting, the level of contrast decreases between black words written on a white page, and to read you may have to pull the book closer to your eyes. As you do this, the ciliary muscle around the lens of your eye contracts, reshaping it so that light flooding in is redirected to a focal point at the back of the eye. As all this eyeball adjusting occurs, many people report headaches and even nausea, the reason being they become tense from muscles that are working harder than normal to focus images; what’s causing the headache is not so much the darkness as staring at something very close to your face.

Most doctors say the discomfort is completely harmless, but a few say that young children may increase their chances of becoming nearsighted when they put too much strain on their eyes. They point to studies that have linked high incidences of myopia to cultures that encourage reading and formalized education among their youth.

One such study says that the strain of reading, and especially of reading in the dark, could give undeveloped eyes a signal to grow in the wrong way; how eye shape develops is important because nearsightedness occurs when the eye grows overly elongated. Almost all infants are born farsighted because their eyes have not yet grown to the right shape–one in which light penetrates the eye and lands on the point of highest acuity in the back of the eye (the fovea). During the first decade of life, the eyes change slightly in shape and size, significantly impacting how the eye focuses.
What scientists do not yet know for sure is which factors direct the eye during these crucial growing years. Most data show that genetics play a huge part, with the likelihood of being myopic increasing tremendously if your parents are as well.

But some preliminary animal research suggests that there could be an environmental element at work as well. It’s possible that while the eye is growing it’s experimenting with how to focus on the world around it, trying on new shapes to find out the best way to turn light into image; think of it as ocular puberty. Doctors theorize that if you strain the eye during this time by forcing it to focus on near objects, you could upset this process of growth.

Even if these findings are true, it is only relevant to the developing eye. Adults reading in the dark should be more concerned about why they didn’t pay their electricity bill than about potentially harming their eyes. But, in the remote chance that you are a child prodigy reading these lines from an unlit crib…well, then you might consider turning on a light.

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  1. Wow – I understand that it is indeed necessary to avoid headaches, but seriously; “…linked high incidences of myopia to cultures that encourage reading and formalized education among their youth.” Correlation is not causation. The plural of anecdote is not data.

    It’s quite easy to find irrelevant information and use it as “data”. Well, it’s not data, it’s just findings. Findings are what is used to get closer to an answer. To say that cultures that encourage reading have a higher chance of being myopic is like saying gay men have a higher chance of having sex with other men.

    Cultures that don’t value reading won’t place as high of standard on eyesight. Macroscopic vision isn’t important to cultures that hunt and fish more than anything else. I expect that tribes in unexplored areas have eyesight issues, they just don’t care. If their near-sightedness leads them to fall off of a cliff, I bet there isn’t an eye doctor sitting in their office saying “I told you so”.

    Joe, April 21, 2009 at 5:00 pm
  2. I don’t know if it’s related, but I would read for hours with the book very close to my face. I now wear glasses.
    I also might see the relation only because my parents said that would happen. It could be genetic, both my parents wear glasses (that could be proven or disproven.) Or it could be something else entirely.

    Blaze, November 22, 2010 at 11:47 pm
  3. Thank you very much, it helped me with my science fair project!

    anonymous, March 8, 2011 at 9:11 pm
  4. Always wondered about that. I read my book in low light sometimes.

    TheReviewer, April 5, 2011 at 5:10 pm
  5. I read in the dark all the time as a kid. I couldn’t put down those choose your own adventure books. My eye sight is better than normal at 15/20. I think in the correct amount of time as an exercise it can be benificial to read in to dark or other simular exercises.

    Matt Bass, September 12, 2011 at 11:23 am
  6. In 4th grade and beyond I frequently read in very low light, and now at 10th grade, I have horrible vision (I almost failed my physical for swim camp because I forgot my glasses) and I always thought it was my fault, as nobody else in my immediate family has issues with vision!!! Now, if only my mom will believe this….

    Eat.Swim.Read, December 24, 2011 at 6:02 pm
  7. Interesting. According to Malcolm X he had 20 20 vision till he read for long nights in the darkness of his prison cell.

    Jake, December 25, 2011 at 2:28 pm
  8. all the links that contains the answers are indeed correct .keep the good job going on thanks

    daniel, January 17, 2013 at 4:55 am
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