red laser pointer

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A research team from the University of Bonn, Germany, and the University of Oxford, U.K., has investigated the severity of injuries that can be caused by common laser pointers. The researchers report that the retinal trauma can sometimes be grave and result in irreversible vision impairment (Dtsch. Arztebl. Int., doi: 10.3238/arztebl.2017.0831).

They conclude that “In view of the practically unimpeded access to laser pointers (even high-performance ones) over the Internet, society at large now needs to be more aware of the danger posed by these devices, particularly to children and adolescents.”

More power, more problems

In recent years, the cost of producing high-power laser diodes has reduced, resulting in reasonably priced, powerful laser pointers that are widely available via the Internet. Thus, use of these products has risen, as have laser-pointer-related eye injuries. While often treated as toys, high-power laser pointers, especially if untested or misclassified, have the potential to cause severe damage to vision.

Noting this trend, the researchers, led by first author Johannes Birtel of the University of Bonn, wanted to take a deeper look at the severity of these injuries. To do so, the team conducted a systematic review of published studies describing 111 patients who experienced acute, permanent damage caused by laser pointers, as well as of seven patients treated in the departments of ophthalmology at the University of Bonn, and at St. Franziskus Hospital, Münster, Germany. The damage ranged from focal photoreceptor defects to macular foramina and retinal hemorrhages associated with loss of visual acuity and central scotoma.

In the blink of an eye

The retina is the primary site of injury caused by photocoagulation—a thermal burn in retinal tissue caused by the absorption of a strong light by the retinal pigment epithelium. Retinal photoreceptors in the vicinity, however, are also at risk, according to the researchers. The extent of a photothermic eye injury depends on wavelength, radiation power, exposure time, localization and spot size.

According to the researchers, “In humans, photocoagulation could be induced at an exposure time of less than 10 s and a power of 5 mW or at a higher output and shorter exposure time.” The team warns that closing one’s eyes or turning away is not always enough to protect your vision. For many—especially children—natural blink reflex times can be inadequate and only partially protect against retinal injury.

Optical coherence tomography (OCT) imaging and other forms of multimodal imaging can be used to detect and follow-up on laser-pointer-related retinal injuries. For the seven clinical cases documented by the team, OCT imaging showed altered retinal reflectivity in all patients, as well as revealing morphological retinal changes such as focal loss or disruption of retinal layers.

Green versus red

One of the findings reported was a higher risk of injury for shorter-wavelength visible light (490-575 nm) than for longer wavelengths (635-750 nm)—green laser pointers and red laser pointers, respectively. In Germany, the optical radiation output of laser pointers is regulated, with a maximum permissible power level 1 mW; other societies permit higher powers (in the U.S., for example, laser pointer power should be below 5 mW). However, the study authors assert that untested and misclassified laser pointers can significantly exceed the 1 mW German limit and emit light in the green spectrum. Also, untested green laser pointers can emit light at different wavelengths, including invisible infrared radiation, which is not true for red laser pointers.

The authors conclude that laser pointers can cause significant and sometimes irreversible retinal damage, warning that treatment options for this kind of injury are very limited. They urge awareness of the danger posed by practically unregulated access to high-performance laser pointers, and they warn that children are particularly susceptible laser-pointer-related injuries.

According to the team, “powerful laser pointers pose a considerable hazard to the eye, and injury can be diagnosed using multimodal imaging and followed-up in the long term … In addition to potential governmental regulatory measures, public awareness of laser pointer injuries needs to be heightened.”

[Updated 2/16/2018 to clarify that the regulation limiting laser pointers to 1 mW output power is specific to Germany.]