MGH Wellman Center for Photomedicine Laser Safety A laser can project more energy at a single wavelength within a narrow beam than can be obtained from more powerful conventional light sources

Electromagnetic Waves Light is a small segment of the electromagnetic spectrum that extends from radio waves to g-rays. The only difference among the different waves is the wavelength (frequency).

Electromagnetic Waves (Light) Transport Energy Radiant power or Radiant flux: Total power emitted in the form of radiation (Watt) Irradiance: Power carried per unit area (W/cm2) Radiant exposure: Energy delivered per unit area (Joule/cm2)

LASER Light Amplification by Stimulated Emission of Radiation Differences between lasers and conventional light sources: Laser Conventional sources Monochromatic Many wavelengths Collimated Emitted in many directions Coherent Incoherent

Cross Section of a Common Laser Ruby Laser

Lasers vs. Conventional Light Sources LED (Light Emitting Diode) Nd:YAG Laser Source: Google

Lasers vs. Conventional Light Sources ( a Apparent visual angle laser source A collimated beam can be focused to a small spot on the retina Conventional light source info.tuwien.ac.at/iflt/safety/section1/s1_body.htm

Light-Tissue Interactions Tissue Absorbers

Light-Tissue Interactions Selective Photothermolysis Medical procedures can only be initiated by absorption of light Effects can be controlled by choosing the appropriate wavelength

Widely-Used Lasers Wavelength of Operation Source: Shore Laser Center

Standards for Safe Use of Lasers Federal and State Agencies OSHA FDA (Center for Devices and Radiological Health) The Commonwealth of Massachusetts: Department of Public Health

Laser Beam Hazards Eye hazard Skin hazard

Laser Hazard Classification Accessible Emission Limit (AEL) Lasers and laser systems are classified on the basis of the laser radiation accessible outside the laser during the intended use and to which the human eye or skin is possible to be exposed

Laser Hazard Classification Class 1 laser: Low power; Considered safe Class 2 laser: Eye protection afforded by the eye blink response Class 3 laser: Medium power; Hazard to the eye from direct exposure Class 4 laser: High power; Hazard to the eye and skin from direct and reflected exposure; Fire hazard

Beam Hazards Eye Hazard Cornea/lens hazard: 290-400 nm and 1400-10,600 nm Retinal hazard region: 400 - 1400nm Eye entering the eye is focused. The irradiance on the retina can be increased as much as 100,000 One central fovea laser hit can cause blindness

Eye Injury Nd:YAG (1064 nm) - Permanent damage Individual saw a white flash, heard a click, then immediately a dark spot in visual field (www.ucl.ac.uk/uro-neph/ppt/lm221102.ppt)

How do you know if you have an eye injury? Exposure to infrared high-power laser causes a burning pain to the cornea or sclera Exposure to visible lasers causes a bright color flash of the emitted wavelength and an after image of a complementary color Exposure to short pulsed infrared lasers may go undetected or may cause a popping sound followed by visual disorientation

Beam Hazards Skin Hazard Visible and infrared high-power lasers can cause permanent skin damage or damage to underlying organs Examples of skin response to laser exposure: Mild to severe reddening Blisters and charring De-pigmentation Ulceration Scarring

Maximum Permissible Exposure MPE Irradiance (Radiant Exposure) to which a person can be exposed without hazard to eye or skin MPE values may cause discomfort

Maximum Permissible Exposure The MPE depends on the following parameters: Laser wavelength Duration of exposure The MPE for eye exposure is much lower than the MPE for skin

Warning Signs Example: Class 2 Laser

Warning Signs Example: Class 4 Laser

Protective Eyewear Goggles

Protective Eyewear

Protective Eyewear The protection wavelength(s) and the corresponding attenuation are scribed on the eyewear The attenuation is given in Optical Density (OD). An OD of 4 means that the irradiance of the beam passing through the eyewear is attenuated by 10,000 times

Non-Beam Hazards Fire: Ignition of materials can occur from direct or intense reflected or scattered beams Electrical: Most deaths caused by lasers are caused by electrocution. Laser capacitors can retain high energy charges even when the power is off

Non-Beam Hazards Laser-generated airborne contaminants: Chemical fumes, aerosols of biological contaminants including viable viruses and other biohazards can and do exist in the laser plume Chemical: Laser dyes, solvents and gases used may be toxic, explosive or carcinogens

Credentialing Procedure Certification to Operate a Particular Type of Laser It is the policy of the Massachusetts General Hospital that all medical staff utilizing a laser for any procedure must be credentialed. The credentialing process must be followed for each type (wavelength) of laser for which privileges are requested

Credentialing Procedure Certification to Operate a Particular Type of Laser Attendance at an approved didactic course Supervised operation with the particular laser in at least 3 patients. For new or experimental lasers, the laser manufacturer can provide hands-on instruction Application for laser credentials to Laser Safety Committee A baseline fundoscopic eye examination that notes apparent pre-existing abnormalities is recommended