3-D effects uncover common vision problems

When Shannon Wyatt, 28, went to see "Avatar" in 3-D last winter, everyone around her marveled that they felt as if they were swimming with jellyfish-like creatures on the planet Pandora. Wyatt only felt dizzy and got a headache.

"I got really sick in it," says Wyatt, who lives outside Chicago. "I thought it was partially animated and partially not." She chalked up her reaction to exhaustion.

But soon after seeing "Avatar," Wyatt got a chance e-mail from an optometrist acquaintance warning of something he called "3-D vision syndrome." She decided to check it out and discovered she had a vision problem - only one of her eyes turns inward to track an object close to her face - that makes 3-D effects a letdown at best and painful at worst. She now thinks that her convergence insufficiency, as it is called, helps explain years of problems focusing on objects up close.

"Watching all this 3-D stuff can unmask problems that have been there a long time," says her optometrist, Dominick Maino.

According to a recent statement from Britain's Royal College of Ophthalmologists, about 2 to 3 percent of people have eye conditions such as Wyatt's that make the eye-popping effects of 3-D fall entirely flat.

With "Avatar" having rapidly become the highest-grossing film of all time, many more 3-D movies are in the works. ESPN broadcast 18 World Cup soccer matches in June on its new 3-D channel, and television manufacturers are churning out sets that promise to put viewers right in the action. As a result, eye specialists say they expect to see more people discovering eye conditions they didn't know they had.

To generate the three-dimensional effect, a special projector displays two images on the screen: They show the same object, but they are filmed or drawn from slightly different angles. You can see this effect by holding up your thumb and looking at it first with one eye closed and then the other: Your thumb will appear to shift position ever so slightly.

Without glasses, the screen looks blurry, but special polarized specs force one of the images to enter the left eye and the other to enter the right. (Cheaper 3-D glasses, with paper frames and one blue and one red lens, do the same thing.) These two images travel to the visual cortex, the area of the brain primarily responsible for processing vision, which correlates them into one pop-out image. This creates this illusion of three dimensions.

"It's not really in our eyes at all," explains Robert Shin, a neuro-ophthalmologist at the University of Maryland Medical Center in Baltimore. "The illusion of three dimensions is something that comes out of our brain."

Wyatt's convergence insufficiency is one of several eye conditions that can cause 3-D movies to fall flat. Poor vision in one eye due to cataracts, glaucoma or retinal problems can cause 3-D problems, as can a "lazy eye" (amblyopia) and strabismus, a condition in which one eye turns inward or outward, Shin says. People with these conditions either won't see 3-D images at all or will feel eye strain or headaches.

"The good news is you cannot hurt your eyes - or your brain, for that matter - watching 3-D movies, even for a really prolonged period of time," Shin says. "If you get a headache, it doesn't mean you need to rush to the eye doctor because something is horribly wrong with your eyes. It just means that, for whatever reason, your brain isn't comfortable seeing 3-D and you shouldn't do it."

That said, if a moviegoer experiences double or blurred vision, headaches or balance problems inside AND outside the theater, he or she might want to consult a doctor to see if there's an underlying eye condition that needs correction, Shin says.

Treatments for eye conditions that cause 3-D viewing problems include surgery for cataracts and glasses or contacts to correct poor vision in one eye.