Types of Lasers
Several classes of laser are in use today. The class definition is based on the power (watts) of the laser. Class 1 includes CD players, laser printers, and supermarket scanners and are not hazardous (1,2). Class 2 has a wavelength of 400-700nm, power limited to 1 milliwatt (1mW), and includes laser pointers and bar code scanners. Class 2 lasers are generally considered safe (1,2). 3A is 1-5mW and includes certain therapeutic lasers, laser pointers, and firearm sights. Eye injury can occur but is not common with class 3A (1
). 3B has power limited to 500mW (0.5 W) and broad therapeutic range. Class 4 has a power greater than 3B, and includes surgical and industrial cutting lasers (30-100 W) and therapy lasers (1-15 W).
Both classes 3 and 4 can cause permanent retinal damage and require the use of special protective glasses based on the wavelength of the specific unit being used (2).
Class 4 lasers may also have a greater risk of skin damage and fire hazard, so safety protocols are generally used, such as scanning technique rather than point to point treatment (1). Despite safety concerns, the advantage to higher powered lasers is more rapid treatment time and potentially deeper tissue penetration. There are newer subclasses of 1M and 2M that use large diameter or divergent beams that may improve safety by pulsing the power settings to allow for therapeutic application without high power output (2). As an aside, LED (light emitting diode) devices are not considered true laser therapy devices because the beams are not coherent, even though they do appear to have therapeutic benefit (3).
Class 3 and 4 are most commonly used for therapy, although 1M appears to be gaining popularity. The biggest difference between the options is the amount of time the treatment takes for a given area and the depth of tissue penetration.