Laser pointers help up to the light. A risk assessment

For several years, small hand-held lasers have been available to the general public, incorporated into items such as pens, key rings, pocket-knives and credit cards. These small diode lasers emit red light with a power varying between one and five milliwatts. Such devices were originally intended as pointers, for use by people making presentations or giving lessons. However, being cheap and compact, they are often now used as novelties, with the result that one comes across them on the street, in discotheques and in classrooms. Lasers of this kind are often labelled as class 3A, in accordance with the American ANSI classification system, when for the European market they should in fact be labelled class 3B, implying that they are capable of causing eye injuries.

More powerful lasers can cause retinal lesions. Exposure limits have accordingly been formulated, the first being put forward in the early seventies. The nominal ocular hazard distance (NOHD) can be calculated from the output power, the aperture and the divergence of the beam. A person who is further from the source than the NOHD is not exposed in excess of the maximum permissible exposure (MPE) levels. For most laser pointers, the NOHD is between five and fifteen metres.

MPE levels are based on ED50 data obtained from experiments with laboratory animals. (An ED50 level is the exposure level at which 50 per cent of the subjects in a test sustain a lesion.) An analysis of the relationship between, on the one hand, ED50 levels and other such data and, on the other, MPE levels shows that eye injuries are very unlikely at levels of exposure around the MPE levels.

Several European countries, including the Netherlands, have decided that class 3A and 3B lasers are suitable only for professional use by adequately trained individuals. In these countries, the sale of class 3A and 3B laser pointers and the incorporation of class 2 lasers in toys are prohibited. In most cases, these measures have been introduced following incidents which apparently involved eye injuries. However, not a single case of permanent eye injury attributable to a laser pointer could be found in the international peer-reviewed literature. Nor were any cases of permanent eye injury reported in a survey of Dutch ophthalmologists.

Nevertheless, exposure to low-power lasers can cause flash-blindness and induce strong aversion responses. The seriousness of such problems depends on the output power of the laser, the ambient light level and the duration of exposure. Unexpected exposure can be dangerous, especially if the person in question is engaged in an activity which requires his or her full concentration, such as driving.

The ban on the sale of higher-power laser pointers in the Netherlands helps to prevent misuse and laser-related problems. It also ensures that more powerful laser pointers capable of causing permanent eye injury cannot be brought onto the market in the future.