Class IIIb: IIIb lasers are hazardous to the eye when viewed directly. For visible and infrared devices, emission power is limited to 0.5W. Protective eyewear, key switches, and safety interlocks are required safety features.
Class IV: Class IV includes all lasers that emit powers in excess of the IIIB limitation of one half of one-watt. Eye protection is needed to limit both direct and diffuse reflected exposure. Key switches and safety interlocks are also required safety features. The majority of scientific, industrial, military, and surgical lasers are in this category.
Power: Class IIIb lasers are limited to a maximum power of a 0.5 Watt. Class IV therapy lasers typically enable the user to select from powers of a 0.5W up to 15 Watts. Increased power enables the clinician to treat a larger area in a shorter period of time, thus allowing an efficient delivery of a therapeutic dose to target tissues.
Treatment Strategies: Due to their power differences, Class IIIb and Class IV laser treatment strategies vary. Class IIIb lasers are often used to treat single points or a group of small points and are held in one place for the duration of the treatment time at each point. When treating with a Class IV therapy laser, the clinician may treat a much larger area, (ex. 300 cm2 for the anatomical area of a large dog’s hip); the treatment head is moved throughout the duration of the treatment to ensure a therapeutic dose of energy is being delivered evenly to the entire target area and its associated tissues. Class IV laser therapy can also be administered using contact or non-contact treatment heads.
Dosing Strategies: Relative to Class IV lasers, Class IIIb lasers deliver a smaller dose of Joules to a smaller area of tissue. Typically treatments are confined to discrete points. A potential weakness of this technique is the variability of clinical results due to the exact placement of the treatment points. The foundation of Class IV laser therapy is based on the delivery of a therapeutic dose of Joules to a large area of target tissue, reducing variability in outcomes. For example, on the lumbar spine of a large dog, to deliver an effective dose for arthritis of 10 Joules/cm2, a Class IV therapy laser set at 10 Watts in continuous wave would deliver 6,000 Joules of energy in a 10 minute treatment session. It would take a 0.5 Watt Class IIIb laser 200 minutes to deliver the same dose.
Wavelengths: Different therapeutic lasers often have different treatment wavelengths ranging from 700 nm to 980 nm. All wavelengths in this therapeutic window target the same photo-active chromophores. The main difference between wavelengths is the absorption of the light by tissue components such as water and melanin.
