A 15-year-old Swiss boy attempted to create his own laser show using a laser pointer he bought on the Internet and a mirror. Instead, he inadvertently beamed the laser into his eyes, creating permanent damage to his vision.

"These high-power laser products are very dangerous," said Dr. Martin Schmid, in a letter in the Sept. 9 issue of the New England Journal of Medicine.

Schmid said that part of the problem is that not all laser pointers are labeled properly, so it's not always easy to know if you have a pointer that could create serious damage. One sure way to know if you have a potentially dangerous laser pointer is if the laser can burn through paper, explained Schmid.

"Every laser pointer which is capable of burning holes into paper or of lighting matches or of popping balloons is highly dangerous for the eye and must not be used by non-professionals," he cautioned.

The teen said that the laser beam hit his eyes several times. Although he immediately noticed that his vision was blurry, he was afraid to tell his parents what had happened. He waited two weeks before letting them know that he was still experiencing blurred vision.

The vision in his left eye was so damaged that he couldn't count how many fingers a doctor was holding up until they were just three feet away. His visual acuity in his right eye was 20/50.

When the teenager's eyes were examined, doctors discovered that there had been significant internal bleeding in the left eye and that there were several small scars in the right eye. Even with treatment, there's still a scar that diminished the boy's vision in his left eye. However, his visual acuity has returned to near normal, according to the report.

The laser used by the boy produced an output of 150 milliwatts (mW), far above the maximal output of 5 mW that's expected from a laser pointer sold to the public. The authors point out that it's possible to purchase laser pointers as strong as 700 mW, although such a device may not look any different than a lower-powered device.

Additionally, Schmid said there are instructions available over the Internet for turning low-power devices into high-powered ones.

Dr. Roy Chuck, chair of ophthalmology and visual sciences at the Albert Einstein College of Medicine in New York City, said that children shouldn't have access to laser pointers. "They're not giving presentations, so why would they need to have them?" He said that when it comes to laser toys -- like those used for laser tag -- buying a well-known name brand may be helpful in this case. "When you're buying off the Internet, it's not as regulated and you just can't tell what the strength of the laser is," noted Chuck.

And, even if you've purchased a "safe" laser toy, it's possible that creative children may turn to the Internet and figure out ways to boost the power of the laser. "By searching YouTube for 'burning laser pointers,' you will find a huge amount of videos showing such dangerous experiments. Moreover, there is an increasing number of homepages and videos demonstrating how to turn legal low-power lasers into burning, high-power lasers," said Schmid.