MGH Wellman Center for PhotomedicineMGH Wellman Center for Photomedicine

Laser SafetyLaser Safety

A laser can project more energy at a single A laser can project more energy at a single

wavelength within a narrow beam than can wavelength within a narrow beam than can

be obtained from more powerful be obtained from more powerful

conventional light sourcesconventional light sources

Electromagnetic WavesElectromagnetic Waves

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

Electromagnetic Waves (Light) Transport Electromagnetic Waves (Light) Transport

EnergyEnergy

Radiant power or Radiant fluxRadiant power or Radiant flux::

Total power emitted in the form of radiation Total power emitted in the form of radiation

(Watt)(Watt)

IrradianceIrradiance::

Power carried per unit area (W/cmPower carried per unit area (W/cm22))

Radiant exposureRadiant exposure::Energy delivered per unit area (Joule/cmEnergy delivered per unit area (Joule/cm22))

LASERLASER

LLight ight AAmplification by mplification by SStimulated timulated EEmission of mission of

RRadiationadiation

Differences between lasers and conventional light Differences between lasers and conventional light

sources:sources:

LaserLaser Conventional sourcesConventional sources

MonochromaticMonochromatic Many wavelengths Many wavelengths

CollimatedCollimated Emitted in many directionsEmitted in many directions

CoherentCoherent IncoherentIncoherent

Cross Section of a Common LaserCross Section of a Common Laser

Ruby LaserRuby Laser

Lasers Lasers vs.vs. Conventional Light Sources Conventional Light Sources

LED (Light Emitting Diode)

Nd:YAG Laser

Source: Google

Lasers Lasers vs.vs. Conventional Light Sources Conventional Light Sources

info.tuwien.ac.at/iflt/safety/section1/s1_body.htminfo.tuwien.ac.at/iflt/safety/section1/s1_body.htm

(a

Apparent visual angle

laser sourcelaser sourceA collimated beam can be focused to aA collimated beam can be focused to asmall spot on the retinasmall spot on the retina

Conventional light sourceConventional light source

Light-Tissue InteractionsLight-Tissue Interactions

Tissue AbsorbersTissue Absorbers

Light-Tissue InteractionsLight-Tissue Interactions

Selective PhotothermolysisSelective Photothermolysis

Medical procedures can only be initiated by Medical procedures can only be initiated by

absorption of lightabsorption of light

Effects can be controlled by choosing the Effects can be controlled by choosing the

appropriate wavelength appropriate wavelength

Widely-Used LasersWidely-Used Lasers

Wavelength of OperationWavelength of Operation

Source: Shore Laser CenterSource: Shore Laser Center

Standards for Safe Use of Lasers Standards for Safe Use of Lasers

Federal and State AgenciesFederal and State Agencies

Federal:Federal:

OSHAOSHA

FDA (Center for Devices and Radiological Health)FDA (Center for Devices and Radiological Health)

The CommonwealthThe Commonwealth of Massachusetts:of Massachusetts:

Department of Public HealthDepartment of Public Health

Laser Beam HazardsLaser Beam Hazards

Eye hazardEye hazard

Skin hazardSkin hazard

Laser Hazard ClassificationLaser Hazard Classification

Accessible Emission Limit (AEL)Accessible Emission Limit (AEL)

Lasers and laser systems are classified on the Lasers and laser systems are classified on the

basis of the laser radiation accessible outside the basis of the laser radiation accessible outside the

laser during the intended uselaser during the intended use

and to which the human eye or skin is and to which the human eye or skin is

possible to be exposedpossible to be exposed

Laser Hazard ClassificationLaser Hazard Classification

Class 1 laser:Class 1 laser:Low power; Considered safeLow power; Considered safe

Class 2 laser:Class 2 laser:Eye protection afforded by the eye blink responseEye protection afforded by the eye blink response

Class 3 laser:Class 3 laser:Medium power; Hazard to the eye from direct Medium power; Hazard to the eye from direct exposure exposure

Class 4 laser:Class 4 laser:High power; Hazard to the eye and skin from High power; Hazard to the eye and skin from direct and reflected exposure; Fire hazarddirect and reflected exposure; Fire hazard

Beam HazardsBeam Hazards

Eye HazardEye Hazard

Cornea/lens hazard: Cornea/lens hazard: 290-400 nm and 1400-10,600 290-400 nm and 1400-10,600

nmnm

Retinal hazard region: Retinal hazard region: 400 - 1400nm400 - 1400nm

Eye entering the eye is focused. The irradiance on Eye entering the eye is focused. The irradiance on

the retina can be increased as much as 100,000the retina can be increased as much as 100,000

One central fovea laser hit can cause blindnessOne central fovea laser hit can cause blindness

Eye InjuryEye Injury

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

How do you know if you have an eye injury?How do you know if you have an eye injury?

Exposure to infrared high-power laser causes a Exposure to infrared high-power laser causes a

burning pain to the cornea or scleraburning pain to the cornea or sclera

Exposure to visible lasers causes a bright color Exposure to visible lasers causes a bright color

flash of the emitted wavelength and an after flash of the emitted wavelength and an after

image of a complementary colorimage of a complementary color

Exposure to short pulsed infrared lasers may go Exposure to short pulsed infrared lasers may go

undetected or may cause a popping sound undetected or may cause a popping sound

followed by visual disorientationfollowed by visual disorientation

Beam HazardsBeam Hazards

Skin HazardSkin Hazard

Visible and infrared high-power lasers can cause Visible and infrared high-power lasers can cause

permanent skin damage or damage to underlying permanent skin damage or damage to underlying

organsorgans

Examples of skin response to laser exposure:Examples of skin response to laser exposure:

Mild to severe reddeningMild to severe reddening

Blisters and charringBlisters and charring

De-pigmentationDe-pigmentation

UlcerationUlceration

ScarringScarring

Maximum Permissible ExposureMaximum Permissible Exposure

MPEMPE

Irradiance (Radiant Exposure) to which a person Irradiance (Radiant Exposure) to which a person

can be exposed without hazard to eye or skincan be exposed without hazard to eye or skin

MPE values may cause discomfortMPE values may cause discomfort

Maximum Permissible ExposureMaximum Permissible Exposure

The MPE depends on the following parameters:The MPE depends on the following parameters:

Laser wavelengthLaser wavelength

Duration of exposureDuration of exposure

The MPE for eye exposure is much lower than the The MPE for eye exposure is much lower than the

MPE for skinMPE for skin

Warning SignsWarning Signs

Example: Class 2 LaserExample: Class 2 Laser

Warning SignsWarning Signs

Example: Class 4 LaserExample: Class 4 Laser

Protective EyewearProtective Eyewear

GogglesGoggles

Protective EyewearProtective Eyewear

Protective EyewearProtective Eyewear

The protection wavelength(s) and the The protection wavelength(s) and the

corresponding attenuation are scribed on the corresponding attenuation are scribed on the

eyeweareyewear

The attenuation is given in Optical Density (OD). The attenuation is given in Optical Density (OD).

An OD of 4 means that the irradiance of the beam An OD of 4 means that the irradiance of the beam

passing through the eyewear is attenuated by passing through the eyewear is attenuated by

10,000 times 10,000 times

Non-Beam HazardsNon-Beam Hazards

Fire:Fire:

Ignition of materials can occur from direct or Ignition of materials can occur from direct or

intense reflected or scattered beamsintense reflected or scattered beams

Electrical:Electrical:

Most deaths caused by lasers are caused by Most deaths caused by lasers are caused by

electrocution. Laser capacitors can retain high electrocution. Laser capacitors can retain high

energy charges even when the power is offenergy charges even when the power is off

Non-Beam HazardsNon-Beam Hazards

Laser-generated airborne contaminants:Laser-generated airborne contaminants:

Chemical fumes, aerosols of biological Chemical fumes, aerosols of biological

contaminants including viable viruses and other contaminants including viable viruses and other

biohazards can and do exist in the laser plume biohazards can and do exist in the laser plume

Chemical:Chemical:

Laser dyes, solvents and gases used may be Laser dyes, solvents and gases used may be

toxic, explosive or carcinogenstoxic, explosive or carcinogens

Credentialing ProcedureCredentialing Procedure

Certification to Operate a Particular Type of Certification to Operate a Particular Type of

LaserLaser

It is the policy of the Massachusetts General It is the policy of the Massachusetts General

Hospital that all medical staff utilizing a laser for Hospital that all medical staff utilizing a laser for

any procedure must be credentialed. The any procedure must be credentialed. The

credentialing process must be followed for each credentialing process must be followed for each

type (wavelength) of laser for which privileges are type (wavelength) of laser for which privileges are

requestedrequested

Credentialing ProcedureCredentialing Procedure

Certification to Operate a Particular Type of Certification to Operate a Particular Type of

LaserLaserAttendance at an approved didactic courseAttendance at an approved didactic course

Supervised operation with the particular laser in at least Supervised operation with the particular laser in at least

3 patients.3 patients.

For new or experimental lasers, the laser manufacturer For new or experimental lasers, the laser manufacturer

can provide hands-on instructioncan provide hands-on instruction

Application for laser credentials to Laser Safety Application for laser credentials to Laser Safety

CommitteeCommittee

A baseline fundoscopic eye examination that notes A baseline fundoscopic eye examination that notes

apparent pre-existing abnormalities is recommendedapparent pre-existing abnormalities is recommended