Education key to safe use of laser pointers
While behind the wheel of his bus in the UK, a driver was startled by an intense, bright light. Though he was not hurt, the driver was frightened, fearing that his vision might be permanently damaged. Later, it was discovered that he had been the victim of a prankster using a laser pointer--a "dangerous weapon," said the driver.
Incidents like this are occurring with greater frequency across the USA and the UK. A debate has ensued in the media and among laser safety professionals, who are trying to sort out the real hazards of laser pointers from the mythical ones.
Government agencies are crying foul, too. Last November, the UK banned Class 3a pointers from commercial sale. A month later, the US Food and Drug Administration (FDA) issued a press release warning against allowing juveniles to use the devices. The UK ban followed research conducted at Heriot-Watt University (Edinburgh, Scotland), which concluded that 14 of the 17 pointers tested were classified incorrectly and were "potentially dangerous" with "a serious potential for eye injury."
Experts in the USA disagree. "I think they are overstating the case," says LIA past president and safety committee chairman David Sliney of the US Army`s Optical Radiation Program. "Just because you are dealing with a laser that is capable of exposing a person to a level above the Maximum Permissible Exposure (MPE) doesn`t necessarily mean that anybody will receive an injury. The MPEs assume a lot of worst-case viewing conditions."
Experts agreeing with Sliney give numerous reasons why the risk of a permanent injury from a laser pointer is practically nil. Because its output power does not exceed 5 mW, most or all of the beam from a laser pointer would have to enter the pupil for more than a momentary sweep to cause injury (see figure). Although designs vary, pointer beams are at least 2 mm in diameter while the human pupil is 2-7 mm, depending on light conditions. Directing the beam purposefully into such a small area would require incredible luck or amazing marksmanship!
Assuming such exposure occurred, however, the eye`s built-in aversion response would still prevent an injury. The aversion response is the natural, physiological instinct to blink or turn away from bright light. It occurs in less than 0.25 s, which is not enough time for a laser beam of less than 5 mW to cause injury, experts say.
Secondary hazards possible
Rather than a permanent retinal burn, then, the real hazards associated with laser pointers are the momentary effects laser experts refer to as glare, flashblindness, and afterimage, all of which can cause secondary hazards--for example, the driver mentioned earlier might have caused a traffic accident. To date, however, there are no known instances where secondary effects have resulted in such an unfortunate incident, but the potential is there.
Glare is generally considered vision loss only when a bright light source is present. Flashblindness is a similar effect that persists after exposure to a bright light. Afterimage is the perception of light, dark, or colored spots that follow exposure to a bright light and can last several minutes.
Other possible hazards result from the psychological effect of being exposed to a laser pointer. "We`ve had people who have had such strong aversion responses that they rub or stick a finger in their eyes, causing a cornea injury that is unrelated to the laser radiation," says Bruce Stuck, Medical Research Detachment director at Brooks Air Force Base in San Antonio, TX. Stuck has been conducting laser glare studies for more than ten years.
As did the bus driver in the UK, people hit in the eye with light from laser pointers also experience worry and fear, causing many of them to overstate the effects they experience, David Sliney says. Some individuals have complained of decreased vision for days, even months, after exposure. This psychological effect has become known as "laser rage" by many laser safety experts. "We can`t otherwise explain why some individuals have described such visual effects. Under controlled conditions, [the effects] would not be that great with a laser pointer," Sliney says.
Educating the public
Once the hazards are identified, of course, the question becomes what to do about them. The consensus reached at the ANSI Z136 committee meeting on May 27-28 in Rockville, MD, was that educating the public rather than further regulating or banning pointers was the answer. "People just need to use them wisely as they would a hammer or a saw or any other dangerous thing we deal with every day," Stuck says.
The Laser Institute of America is leading the charge for laser pointer education, spreading the word in various print media about using lasers wisely (see "Laser pointer tips," below). Rockwell Laser Industries (Cincinnati, OH) maintains a database of laser accidents that includes pointer incidents. The FDA`s Center for Devices and Radiological Health (CDRH) steadily seeks to identify manufacturers who are not classifying products correctly or who are selling inappropriate pointers. Also, says Jerry Dennis of the CDRH, the Federal Trade Commission "goes after companies that promote the irresponsible use of laser pointers."
The ANSI Z136 committee also proposed adding a section on laser pointers to the American National Standard Z136.1, For the Safe Use of Lasers. "We think it`s really important to the community to get some information out there," Stuck says. o
The LIA would like to thank Dr. David Sliney for his assistance with this article.
For any distance greater than a few feet, it would be almost impossible to line up a laser pointer beam precisely with the pupil of an eye; even minute fluctuations caused by the holder`s breathing and blood flow through the hand would throw off the beam (top). To cause permanent injury, the full beam must enter the pupil for more than 0.25 s, before which the eye`s instinctive aversion response would be triggered and prevent injury (bottom).