A Swiss boy's sight was seriously damaged by a laser pointer. Laser pointers are those little light-emitting sticks that are used in presentations. While many laser pointers are harmless, there are some very powerful laser pointers and most of them look just like the harmless ones. And it was a powerful laser pointer that caused they Swiss boy's eye injury.

Most of these powerful lasers can be bought as-is, mainly from the Internet. Others are conventional low-power pointers that have been modified to produce a stronger beam.

Keeping powerful lasers out of children's hands may not be an easy thing for parents to do. Just knowing that these devices exist and what the risks are is a first step.

Conventional laser pointers have a power output of 1-5 milliwatts (mW) and are currently considered harmless because the human eye protects itself from them with blink reflexes. The more powerful pointers can have an output of up to 700 mW.

In a letter to the New England Journal of Medicine, a Swiss ophthalmologist describes what happened to a 15-year old boy who got his hands on one such device.

The boy had ordered a 150 mW green laser pointer from an Internet site. While using it to create a light show in front of a mirror, the beam hit his eye several times. He immediately noticed blurred vision in both of eyes but was afraid to tell anyone about this for two weeks. When he finally went to a doctor, the vision in his left eye was so poor, he could only tell how many fingers the doctor was holding up from three feet away or closer.

Further examination revealed significant internal bleeding in the left eye and several small scars in the right. Four months later, there's still a small scar in the left eye, though the boy's vision has returned to near normal after treatment.

All this from a few minutes with a laser pointer.

It's also possible to modify conventional laser pointers so they'll emit a stronger beam. While the process isn't simple, it can be done by someone with the appropriate equipment and a strong enough desire. Such as a technically savvy teenager with a lot of time on their hands.

Stronger laser pointers usually can't be told from weaker ones by sight alone. Anyone using a laser pointer should also use some common sense. Never look into the beam or shine it in anyone's eyes or face. It won't do any good to say later on that you didn't know that the laser was loaded.

It's a fact of life that the stronger laser pointers may prove irresistible to teenagers. Or even adults that haven't entirely left their teenage years behind. Some of the uses the Swiss boy planned for the laser were popping balloons from a distance and burning holes in paper and his sister's sneakers. And that was just the beginning.

Conventional laser pointers put out very little heat. Any laser pointer that can burn a hole through paper or pop a balloon is dangerous. Even a 400 degree oven won't burn paper. A laser pointer that can do so isn't a tool or toy; it's a ray gun, a weapon.

Right now, keeping powerful lasers out of children's hands may not be an easy thing for parents to do. Just knowing that these devices exist and what the risks are is a first step.

The letter detailing the boy's injuries and the dangers of laser pointers was published by the New England Journal of Medicine on September 9, 2010.