Injury reports have been scattered and anecdotal, but eye doctors are warning that recent cases of teenagers who suffered eye damage while playing with high-powered green laser pointers are likely to be the first of many.

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Injury reports have been scattered and anecdotal, but eye doctors are warning that recent cases of teenagers who suffered eye damage while playing with high-powered green laser pointers are likely to be the first of many.

“I am certain that this is the beginning of a trend,” said Dr. Martin Schmid, a Swiss ophthalmologist who reported one such case in September’s issue of The New England Journal of Medicine.

Laser pointers, both red and green, already had been implicated in a ninefold increase over five years in reports of lasers being aimed at planes and helicopters, including some incidents at Seattle-Tacoma International Airport. Pilots in some cases have had to relinquish control of their aircraft to a co-pilot because of vision loss, and there are concerns that terrorists could use lasers to bring down planes.

Federal law already allows charges to be brought against those seeking to destroy an aircraft, but the law requires proof of willful intent to endanger a pilot. To make it easier to prosecute such incidents, the House on Monday passed a measure that would make it a federal crime punishable by up to five years in prison to knowingly aim laser pointers at aircraft.

The Senate passed the same provision last month as an amendment to a Federal Aviation Administration spending bill. The two chambers now must agree on a common format to send it to President Obama for his signature.

The threat from handheld laser pointers has grown as they become more powerful and more affordable. Lasers that once cost more than $1,000 can be bought online for a few hundred dollars or less — even though they are 10 to 20 times as powerful as the legal limit set by the Food and Drug Administration (FDA).

At the American Association of Ophthalmologists, a spokeswoman said the group was unaware of any increase in eye injuries caused by lasers. But doctors interviewed for this article said they were shocked by the easy availability of high-powered lasers.

The laser injuries Dr. Shepard Bryan has seen at his practice in Mesa, Ariz., involved red lasers, which many laser fans consider passé.

A green laser, its beam visible along its path, is even more dangerous. Green is more easily absorbed by the retina than red, so it requires less exposure to cause damage.

A high-school student recently went to see Dr. Robert Josephberg, a retina specialist at Westchester Medical Center in Valhalla, N.Y., complaining of a blind spot in his left eye. The boy, who did not want to be identified, said the injury occurred when a friend waved a green laser pointer in front of his face. (Whether it will heal completely is uncertain.)

Josephberg said he doubted the story at first. “I didn’t believe that a green laser was out there that could cause the damage,” he said.

But it turned out the laser put out 50 milliwatts of power, 10 times the FDA limit. And as he investigated his patient’s case, Josephberg went online and bought a 100-milliwatt pointer for $28. He could hardly believe how easy it was.

Like household lights, lasers are measured in watts, but the similarity ends there. A 100-watt incandescent bulb produces about five watts of visible light; the five-milliwatt laser is only one-thousandth as powerful. But because the light from a bulb is diffuse and a laser beam is concentrated, the effect of five milliwatts on the eye is 10,000 times as intense, according to Samuel Goldwasser, a laser expert and author of the online guide Sam’s Laser FAQ.

Dr. Jerald Bovino of the American Retina Foundation says the way the eye focuses also can intensify the laser.

“It is going to the fovea, the center of the retina,” Bovino said. The darker pigment in the fovea absorbs the light as heat, quickly raising the temperature of the retina the same way a black car seat becomes hot as it absorbs the sun.

Dr. Kimia Ziahosseini of the St. Paul’s Eye Unit at Royal Liverpool University Hospital in England says the dangers are so acute that even the FDA’s five-milliwatt limit is too high.

“Laser pointers available for sale to general public should be less than one milliwatt,” she said. “Anything more than this puts people at risk by the criminally minded or those who are unaware of the risks.”

In a consumer update in December, the FDA said it was aware that illegal laser pointers were being sold and warned that “a higher-powered laser gives you less time to look away before injury can occur, and as power increases, eye damage may happen in a microsecond.”

Daniel Hewett, a health promotion officer at the agency, said by e-mail that the agency had seized products from Wicked Lasers, an online store based in Hong Kong.

Sam Liu, chief executive of Wicked Lasers, said its products did not violate FDA restrictions because those exceeding the five-milliwatt limit were not called pointers.

Moreover, he said, “we make it extremely clear on our Web pages that these lasers are not only eye hazards but fire hazards.” And he said the company would begin offering laser-safety lessons to customers before online checkout.

Several laser experts say the enforcement of regulations already is insufficient and ineffective. “It’s a whole can of worms,” Goldwasser said, recalling that he recently received a 100-milliwatt laser as a gift from Wicked Lasers. To rein in all the hazardous products out there — from virtual stores to flea markets — would be impossible, he said.

And any talk of restricting availability is certain to meet resistance from the large community of laser enthusiasts, including those who use them professionally.

Information from The Associated Press and Seattle Times staff is included in this report.