Hollywood studios and technology companies are pinning growth hopes on a 3D future, but one major drawback with the format is that it makes millions of people uncomfortable or sick.

Optometrists say as many as one in four viewers have problems watching 3D movies and TV, either because 3D causes eye strain or because the viewer has problems perceiving depth in real life. In the worst cases, 3D makes people queasy, leaves them dizzy or gives them headaches.

Researchers have begun developing more lifelike 3D displays that might address the problems, but they are years or even decades from being available to the masses.

But that is not deterring the entertainment industry, which is well aware of the problem, charging ahead with plans to create more movies and TV shows in 3D.

When watching 3D, our eyes track an approaching object by turning inward, towards our noses. Bring something close enough, and we look cross-eyed. 3D screens also elicit this response when they show something approaching the viewer.

The problem is that as the eyes turn inward, they also expect to focus closer.

But a screen isn’t moving closer, so the eyes have to curb their hard-wired inclination and focus back out. This mismatch between where the eyes think the focus should be and where the screen actually is forces them to work extra hard.

“That causes at least part of the discomfort and fatigue that people are experiencing,” says Martin Banks, an optometry professor at University of California, Berkeley.

Research into how 3D screens affect viewers is only in its early stages. There have been no large-scale scientific studies. Based on an unscientific, online survey, the American Optometric Association estimates that 25 per cent of Americans have experienced headaches, blurred vision, nausea or similar problems when viewing 3D.