Laser pointers are as ubiquitous as they are useful. They are safe but dazzling if viewed momentarily. Patients may be concerned about long-term consequences of accidental laser pointer exposures, occasionally consulting attorneys about perceived injuries. Malingerers may allege visual problems after a laser pointer exposure, a problem that has been encountered with high school students. An individual was even prosecuted for assault after deliberately shining a laser pointer into a police officer's eyes.
Most patients are comfortable with an ophthalmologist's reassurance that momentary laser pointer exposure is safe. Other patients want more information, so it is helpful to understand some details about laser pointers and their regulation.
Lasers and their applications are regulated in the United States by standards governing manufacturers to label each laser device with a warning appropriate for its potential hazardousness. Class 1 lasers are considered incapable of causing damaging ocular exposures and do not require control measures. The maximum power output for a visible light laser to be classified as a class 1 device varies with wavelength, ranging from 0.004mW or less for blue or green light to 0.024 mW or less for red light. Class 4 devices are dangerous industrial, military, or medical lasers that generate more than 500mW of laser power. Class 2, 3a, and 3b lasers produce laser power that is less than 1 mW, between 1 and 5 mW, and between 5 and 500 mW, respectively.
Ophthalmologists routinely use power settings between 100 and 500 mW for retinal photocoagulation, so class 3b devices certainly pose a serious ocular risk. Laser pointers are class 3a devices, however, with an output power of less than 5 mW.
Laser pointers currently produce red light, ranging from 632.8 nm for helium-neon to 670 nm for a GaA1As diode. Red light has negligible potential for photic retinopathy, but certainly can cause retinal photocoagulation at high irradiances. As lower wavelength diode lasers closer to the peak of photopic sensitivity (555 nm) become available, the risk of laser pointer phototoxicity will increase but remain negligible. Conversely, the power of laser pointers could be decreased significantly by using wavelengths more sensitive to the human eye. For example, a class 2, 0.12 mW, yellow-green pointer operating at 555 nm has the same apparent photopic brightness as today's typical class 3a, 4mW, 670 nm, red diode.
It is theoretically possible to produce retinal photocoagulation in an eye with perfectly clear ocular media by staring at a collimated class 3a laser beam for more than 10 seconds, so it is important to keep laser pointers away from infants and children. In adults, pupil, blink, and aversion responses terminate accidental laser pointer exposures in less than 0.25 seconds, however, so there is no realistic risk of immediate or delayed retinal damage from momentarily viewing a class 3a laser pointer. Nonetheless, the label of a class 3a red laser pointer cautions users to avoid shining a laser pointer beam into anyone's eye. It makes good sense to follow this advice, just as it is good common sense not to stare into the beam of a 35 mm slide projector or the headlight of an approaching locomotive. |
