mgh wellman center for photomedicine laser safety a laser can project more energy at a single...
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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
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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).
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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))
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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
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Cross Section of a Common LaserCross Section of a Common Laser
Ruby LaserRuby Laser
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Lasers Lasers vs.vs. Conventional Light Sources Conventional Light Sources
LED (Light Emitting Diode)
Nd:YAG Laser
Source: Google
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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
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Light-Tissue InteractionsLight-Tissue Interactions
Tissue AbsorbersTissue Absorbers
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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
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Widely-Used LasersWidely-Used Lasers
Wavelength of OperationWavelength of Operation
Source: Shore Laser CenterSource: Shore Laser Center
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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
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Laser Beam HazardsLaser Beam Hazards
Eye hazardEye hazard
Skin hazardSkin hazard
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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
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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
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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
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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)
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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
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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
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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
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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
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Warning SignsWarning Signs
Example: Class 2 LaserExample: Class 2 Laser
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Warning SignsWarning Signs
Example: Class 4 LaserExample: Class 4 Laser
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Protective EyewearProtective Eyewear
GogglesGoggles
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Protective EyewearProtective Eyewear
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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
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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
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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
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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
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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