Debunking Eye Myths

Burning Question: Does reading in dim light hurt your eyes?

By HEIDI MITCHELL - The Wall Street Journal - 4/8/2013

Mom always told us we'd go blind if we read in the dark. Does science back her up? Jim Sheedy, a doctor of vision science and director of the Vision Performance Institute at Oregon's Pacific University, sets his sights on the truth. 

Dark Matter

Turns out, our parents were wrong. "There is no reason to believe nor evidence to support that any long-term damage to the eyes or change in the physiology to the eyes can be caused by reading in the dark," Dr. Sheedy says. That is not to say that nocturnal page-turning won't lead to discomfort or fatigue. The lack of light will cause the pupils to dilate, resulting in a smaller depth of field—the distance between the nearest and farthest object that the eye considers to be in focus. Dr. Sheedy says the added effort to change focus (called the eye's accommodative system) and the effort to change the angle of the lines of sight between the two eyes (called the vergent system) will likely make your eyes feel tired and your body spent. But, of course, that's often the object of reading under the covers.

Seeing Clearly

Dr. Sheedy says he assures his students that there isn't enough evidence to argue that what you do with your eyes leads to myopia (nearsightedness): "The predominant determinant of myopia is genetics." No link to long-term damage has ever been conclusively shown, says Dr. Sheedy. "It's an old tale, a ploy used by moms to get kids to go to sleep when they wanted them to," he says.

Electronic Age

Reading on a tablet device won't damage your eyes, Dr. Sheedy says. His team has studied various fonts, computer displays and pixel resolutions, and found the difference in effect on the eye between reading e-ink and the printed word to be negligible.  He adds that pixel density and screen resolution have reached the point at which the eye doesn't know which it is seeing. So if reading a printed book in dim light is fine, so is reading a Kindle or iPad.

Moving from Dark to Light

The eyes adapt quickly when going to the light—emerging from a tunnel into the sun, say—but going to the dark "requires the regeneration of photo pigments, and that takes some time to reach full dark-adaptation," says Dr. Sheedy. Adjusting to the dim light next to your bed should only take seconds. But when going from bright light to maximum darkness, studies have shown, eye sensitivity continues to change for up to 25 minutes, he says. Just ask a pirate. "Ever wonder why a pirate wears patches? It's not because he was wounded in a sword fight," says Dr. Sheedy. Seamen must constantly move between the pitch black of below decks and the bright sunshine above. Smart pirates "wore a patch over one eye to keep it dark-adapted outside." Should a battle break out and the pirate had to shimmy below, he would simply switch the patch to the outdoor eye and he could see in the dark right away—saving him 25 minutes of flailing his cutlass about in near blindness.