Watching 3D films such as Avatar could give some viewers headaches, experts have warned.

专家日前警告说，观看《阿凡达》这样的3D电影会让人感到头痛。

Avatar has become the fastest film to make $1 billion in ticket sales.Watching 3D films such as Avatar could give some viewers headaches, experts have warned.

The success of James Cameron's science-fiction blockbuster巨型炸弹，轰动, which has already taken more than $1 billion (£600 million) at the box office票房, is fuelling a surge in popularity for three-dimensional movies and new 3D television sets.

But prolonged延长的，拖延的 viewing may result in an aching head, according to Dr Michael Rosenberg, an ophthalmology眼科学 professor at Northwestern University Feinberg School of Medicine in Chicago.

He said: "There are a lot of people walking around with very minor¹ eye problems, for example a minor muscle imbalance, which under normal circumstances the brain deals with naturally."

Watching a 3D movie confronts viewers with an entirely² new sensory³感觉的，知觉的 experience. "That translates into greater mental effort, making it easier to get a headache," he said.

Dr Deborah Friedman, a professor of ophthalmology and neurology at the University of Rochester Medical Center in New York, said: "If your eyes are a little off to begin with then it's really throwing a whole degree of effort that your brain now needs to exert运用，发挥. This disparity不等，不同 for some people will give them a headache."

Experts say there are no studies tracking how common it is to get a headache after watching a 3D film.

Rick Heineman, a spokesman for RealD, which provides 3D equipment to cinemas, said headaches and nausea⁴恶心，晕船 were the main reasons 3D technology never took off before.

But he said new digital technology addresses many of the problems that had previously⁵ caused sore剧烈的，疼痛的 heads.