Watching 3D films such as Avatar could give some viewers headaches, experts have warned.
The success of James Cameron's science-fiction blockbuster, which has already taken more than $1 billion (£600 million) at the box office, is fuelling a surge in popularity for three-dimensional movies and new 3D television sets.
But prolonged viewing may result in an aching head, according to Dr Michael Rosenberg, an ophthalmology professor at Northwestern University Feinberg School of Medicine in Chicago.
He said: "There are a lot of people walking around with very minor 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 entirely new sensory 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. This disparity 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 nausea were the main reasons 3D technology never took off before.
But he said new digital technology addresses many of the problems that had previously caused sore heads.
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。
詹姆斯•卡梅隆的科幻大片《阿凡达》目前已创下超过10亿美元（6亿英镑）的惊人票房。该片的成功开启了3D电影和3D电视的新时代。
但芝加哥西北大学费恩柏格医学院的眼科学教授迈克尔•罗森堡博士说，长时间观看3D电影可能会导致头痛。
他说：“很多人的眼睛都有点小毛病，比如眼部肌肉轻微不平衡，在正常情况下大脑可以自然应对这种问题。”
观看3D电影会给观众带来一种全新的视觉体验。他说：“这就需要更多的脑力劳动，容易引起头痛。”
纽约罗彻斯特大学医学中心的眼科学和神经学教授戴伯拉•弗瑞德曼博士说：“如果你的眼睛本来就有点小问题，那么在观影时你的大脑就会相当费劲。这种失衡会让有些人感到头痛。”
专家说，现在尚无研究追踪调查人们在看完3D电影后感到头痛的情形究竟有多普遍。
为影院提供3D设备的RealD公司的发言人瑞克•海涅曼说，3D技术一直未兴起的主要原因就是它会让观影者感到头痛和恶心。
但他说，新的数码技术解决了以前导致头痛的很多问题。
Vocabulary:
blockbuster: something, such as a film or book, that sustains widespread popularity and achieves enormous sales 卖座的大片
ophthalmology: the branch of medicine that deals with the anatomy, functions, pathology, and treatment of the eye 眼科学
take off: to achieve wide use or popularity 被广泛使用，受欢迎（a new movie that took off 一部很受欢迎的新电影）