Laser devices, which emit a potentially harmful laser beam, are now widely available to the general public. They are generally sold as laser pointers or laser keychains and are labelled as emitting 5 mW of laser power. According to the American National Standards Institute classification, they are Class 3A products and protection is afforded by the aversion response (including the blink reflex). However, it is the International Electrotechnical Committee (IEC) classification which applies in Europe, and this has an additional restriction. In the United Kingdom and the rest of Europe, for a Class 3A laser the irradiance should be less than 25 W/m2 averaged through a 7 mm diameter pupil. A quick calculation shows that, if the beam is less than 7 mm in diameter, then the laser output power should be no more than 1 mW (which is the Class 2 limit). This is the usual sort of laser pointer, which is in widespread use. A 5mW laser keychain is a Class 3B device, according to European classification. These devices are potentially hazardous and should only be used by persons who have received appropriate training.
During laser treatment of retinal abnormalities, permanent lesions are produced by focusing a laser beam of some 100 mW for 100 msec on to the retina. With a 5 mW beam, the exposure time required to achieve the same energy input will be 2 seconds. Since the eye is not held steady and there is no artificial focusing, the retinal spot size will be larger and so the time to achieve the same energy density will be longer than 2 seconds when using a laser keychain. However, it is quite possible that coagulation will occur after several seconds exposure. By contrast exposure to a 1 mW laser beam is unlikely to produce a thermal lesion because there is insufficient power to raise the temperature of the retina.
The normal aversion response takes about 0.25 sec but it is possible to force oneself to look longer into a bright beam. School children are playing a dangerous game of chicken to see how long they can stare into these laser beams. This means that the normal aversion response may not be assumed, and may not provide adequate protection.
Laser devices emitting more than 1 mW of laser power are potentially dangerous. Class 3B lasers should not be available to the general public, and incorrectly labelled Class 3A devices should be withdrawn from the market. Health professionals should be alerted to the problem, and the public should know that laser pointers and keychains are not playthings.
Harry Moseley(1),(2) and Charles McGhee(3)
The Photobiology Unit(1), Medical Physics Department(2), Eye Department(3),
University of Dundee
Ninewells Hospital & Medical School
Dundee DD1 9SY
Tel: 01382 632240
Fax: 01382 646047
All opinions expressed in the article are the author's alone and not necessarily those of the BMLA, nor should this be taken as an endorsement by the BMLA.