Laser eye surgery to correct short or long sight is neither safe enough nor effective enough to be carried out in the NHS, and doctors who offer it privately must explain the dangers to their patients, an expert advisory body ruled yesterday.

About 100,000 people a year have laser surgery on their eyes, but the National Institute for Clinical Excellence (Nice) says there is not enough evidence yet of possible long-term complications. Studies of patients undergoing the procedure known as Lasik show that the results are not good for those with poorer eyesight, and side effects can be a problem.

Nice, which advises the government on NHS treatments, found that Lasik had better results in people with mild to moderate short sight. In four studies, 63% to 79% of eyes had normal vision after surgery. But in people with moderate to strong short sight, only 26% to 36% had normal vision.

It was not possible to get a full picture of the safety of Lasik, the experts said, because there were no long-term studies. But there were problems, even in the short term. Some patients' eyes got worse. Others had a glare effect or a halo effect around objects at night.

The procedure involves cutting a hinged flap in the cornea so that tissue can be cut away with the laser from the middle layers of the cornea. Sometimes this weakened the cornea.

"Although many people have had Lasik treatment there is very little information about how many suffer complications or damage," said Professor Bruce Campbell, chairman of Nice's interventional procedures advisory committee. More research was needed, he said.