The admonition offered by legions of mothers — “Don’t sit so close to the TV” — isn’t really an option when it comes to e-reading devices. You have to get close to the screen to use it.

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The act of reading is going through a number of radical transitions, but perhaps none is more fundamental than the shift from reading on paper to reading on screens. As consumers decide whether to make this jump and which technology to use, one key question is how reading on a screen affects the eyes.

First of all: doctors say that reading on a screen won’t cause any harm.

“Most of what our mothers told us about our eyes was wrong,” said Dr. Travis Meredith, chair of the ophthalmology department at the University of North Carolina, Chapel Hill. “Sitting close to a television, or computer screen, isn’t bad for our eyes. It’s a variety of other factors that can cause physical fatigue.”

For example, the ergonomics of reading screens and the lack of blinking when we stare at them play a big role in eye fatigue. “The current problem with reading on screens is that we need to adjust our bodies to our computer screens, rather than the screens adjusting to us,” Dr. Meredith said.

Still, as regular readers of Bits comments know, there is a lively debate among fans of e-readers and paper books about which type of reading experience is most friendly to the eyes.

It turns out the answer isn’t as black-and-white as we might assume.

Doctors and researchers note that in most instances, paper can offer more visual sophistication than a screen. But certain types of paper, including inexpensive newsprint and the paper in softcover books, can actually provide an inferior reading experience for our eyes than the electronic alternatives.

With e-readers, there are currently numerous display technologies available, from the black-and-white E Ink technology found in Amazon.com’s Kindle and the Barnes & Noble Nook, to the coming full-color IPS LCD display that will come built into Apple‘s iPad. And then there’s old-fashioned paper. Does one offer a better reading experience than the others?

Michael Bove, director of the Consumer Electronics Laboratory at the M.I.T. Media Lab, says different screens make sense for different purposes.

“It depends on the viewing circumstances, including the software and typography on the screen,” said Mr. Bove. “Right now E Ink is great in sunlight, but in certain situations, a piece of paper can be a better display than E Ink, and in dim light, an LCD display can be better than all of these technologies.”

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E Ink has a very low contrast ratio. Although it can offer an excellent reading experience in bright sunlight, the screens can become uncomfortable to use in dark settings because of the lack of contrast and backlighting on the screen.

LCD screens, meanwhile, have long struggled to offer good viewing angles for reading. Apple’s latest IPS LCD screens include extremely wide viewing angles, but the reflective glass on the screen could be a hindrance in brightly lit situations.

Professor Alan Hedge, director of the Human Factors and Ergonomics Laboratory at Cornell University, said that reducing eye fatigue is less a matter of choosing a specific display than of taking short breaks from looking at the screen.

When we read, Dr. Hedge explained, a series of ocular muscles jump around and can cause strain, regardless of whether we are looking at pixels or paper. “While you’re reading, your eyes make about 10,000 movements an hour. It’s important to take a step back every 20 minutes and let your eyes rest,” he said.

Today’s screens are definitely less tiring to look at than older displays, which refreshed the image much less frequently, causing a flicker. Carl Taussig, director of Hewlett-Packard‘s Information Surfaces Lab, said the 120 Hz refresh rate typical of modern screens is much quicker than our eyes can even see.

“The new LCDs don’t affect your eyes,” Mr. Taussig said. “Today’s screens update every eight milliseconds, whereas the human eye is moving at a speed between 10 and 30 milliseconds.”

Mr. Taussig said consumers will pick the type of screen that makes sense on an individual basis. “I don’t think there is a single technology that will be optimum for all the things we want to do with our devices. For example, H.P. sells 65 million displays a year, and they are all used in a different way.”